Abstract

From 2001 to 2012, the Whooping Crane Eastern Partnership released 196 costume-reared juvenile whooping cranes Grus americana in the eastern United States in an effort to reintroduce a migratory population of this endangered species. Techniques included leading juveniles from Wisconsin to wintering areas by ultralight aircraft or direct release of juveniles in Wisconsin prior to their first autumn migration. With few exceptions, ultralight-led cranes released on the Florida Gulf Coast wintered in inland freshwater habitats in subsequent winters. Wintering of the population occurred in four general regions: Florida–southern Georgia, coastal Carolina, the Mid-South (primarily Tennessee and northern Alabama), and the North (Indiana, Illinois, and Kentucky). Releases of ultralight-led juveniles resulted in the majority of the population returning to winter in Florida during the early years of the reintroduction. Later direct autumn releases and shortstopping by ultralight-led birds increased numbers in the Mid-South. Winter climate played a large role in wintering in the North. Drought resulted in changes in wintering locations, especially in Florida. Other factors influencing changes in distribution included habitat degradation and associations with other whooping cranes, especially new mates and birds released by different techniques. Breeding pairs and direct autumn-released birds exhibited greater winter site fidelity than did nonbreeders or ultralight aircraft-led birds, but fidelity was low for all groups. Causes of mortality differed across the winter range, with predation being most prevalent in Florida and gunshot accounting for the majority of mortalities north of Florida. Because most pairing occurred in central Wisconsin, the widespread winter distribution had no apparent negative effect on pair formation. There was no clear relationship between winter region and subsequent incubation success. The widespread distribution of the population poses minimal risk to the outcome of the reintroduction in comparison to reproduction problems in the core reintroduction area of central Wisconsin.

Introduction

The whooping crane Grus americana, once widespread in interior North America, was decimated by 1900 and is a federally listed endangered species under the U.S. Endangered Species Act (ESA 1973, as amended). The primary distribution included breeding areas from the tallgrass prairies of north-central United States through the aspen Populus tremuloides parklands of the Canadian prairie provinces and wintering areas in the tallgrass prairies and coastal marshes of Louisiana and Texas and the interior grassland plateaus of Mexico (Allen 1952). The last known nesting within the primary distribution occurred in Saskatchewan in 1929 (Hjertaas 1994). A single migratory population (Aransas-Wood Buffalo; hereafter, AWB) survived. That small remnant flock wintered on Aransas National Wildlife Refuge (NWR; hereafter, Aransas) on the Texas Gulf Coast and reached a low of 15 or 16 birds in the winter of 1942 (Boyce 1987). Its nesting area was not discovered until 1954 in Wood Buffalo National Park, Northwest Territories, Canada (Allen 1956). A small nonmigratory population also persisted in the marshes of White Lake, Louisiana, until 1950 (Gomez 1992).

By 1964, the AWB population had increased to 42 individuals. An injured juvenile was captured at Wood Buffalo National Park that year and in 1966 became the first whooping crane in a captive propagation program at Patuxent Wildlife Research Center, Laurel, Maryland. Eggs collected from the AWB population were used to build that and later captive flocks and were a source of founders needed to establish additional populations required for whooping crane recovery (USFWS and CWS 2007). Criteria for reclassifying the whooping crane from endangered to threatened status pursuant to the ESA consist of maintaining ≥40 breeding pairs in the AWB population and 25 breeding pairs in self-sustaining populations at each of two other discrete locations for at least a decade by each population. If only one additional population is reestablished, the AWB population must maintain 100 productive pairs and the new population ≥30 pairs. If no reintroduced populations are successful, the AWB population must remain above 250 productive pairs and 1,000 individuals before the species may be reclassified to threatened status. These recovery criteria underscore the importance of carefully monitoring all aspects of reintroduction efforts and understanding reasons for success or failure so that adaptive management can be applied in both reintroduction and the overall recovery effort for the species.

The first reintroduction attempt began in the Rocky Mountains in 1975 and employed cross-fostering (Drewien and Bizeau 1977). Whooping crane eggs collected by helicopter from nests at Wood Buffalo National Park and produced by the captive flock at Patuxent Wildlife Research Center were substituted for eggs of sandhill cranes Grus canadensis in nests of the latter on Grays Lake NWR, Idaho. The resulting whooping cranes experienced high mortality and failed to reproduce with conspecifics. Cross-fostering was discontinued after the 1988 nesting season (Ellis et al. 1992).

A second reintroduction attempt, to establish a nonmigratory flock, began with release of costume–isolation-reared and parent-reared juveniles from captive propagation into central Florida in 1993. Costume-rearing (Horwich 1989) is a hand-rearing technique in which crane chicks are reared by humans covered with a sheet-like costume and using a crane puppet head; chicks are isolated from exposure to noncostumed humans and human vocalizations during the rearing period. In parent-rearing, an egg or chick is given to a captive pair of whooping cranes, which rear the chick in a pen at a propagation facility (Nagendran et al. 1996). Survival and reproduction of whooping cranes reared by these methods were insufficient to establish a self-sustaining flock in Florida; the last release occurred in 2006, and that reintroduction attempt was discontinued in 2008 (Folk et al. 2010).

A third attempt, to establish a migratory population of whooping cranes in eastern North America (i.e., eastern migratory population), began in 2001. Two reintroduction techniques were used through 2012. Initially, costume-reared juveniles were trained to follow ultralight aircraft (Lishman et al. 1997) and led on migration from central Wisconsin to predetermined wintering areas on the Gulf Coast of Florida. Annual releases of ultralight aircraft-led (UL) cranes and of cranes by direct autumn release (DAR) techniques, the latter beginning in 2005 (Urbanek et al. 2014), have continued through 2012. In DAR, the juvenile whooping cranes were released directly on the northern reintroduction sites to follow older whooping cranes already in the population or wild sandhill cranes on their first autumn migration. Reintroduction locations were changed within Wisconsin in 2011 (see Methods), and release of parent-reared juveniles (described above) was an additional technique used beginning in 2013. Efforts to establish this population continue to date (2014).

A fourth reintroduction, to establish a nonmigratory population in southwestern Louisiana, began with juveniles hatched in 2010 and released in March 2011 (Gomez 2014). Through 2013, all whooping cranes in that flock have been costume-reared.

The third reintroduction attempt, to establish a migratory population in eastern North America, is the topic of this paper. Chassahowitzka NWR (hereafter, Chassahowitzka), Citrus and Hernando counties, Florida, was the original wintering area selected for this population. This coastal area consisted of salt marsh, as did the wintering area of whooping cranes in the natural population at Aransas (Cannon 1998), and minimized possible conflicts with the concurrent reintroduction of nonmigratory whooping cranes in inland central Florida (Folk et al. 2010). Later DAR releases were planned to integrate additional birds into the core population established by the earlier UL releases. However, because of much greater tidal fluctuations, lack of fresh water, soft muck substrate, and dense vegetation, habitat on Chassahowitzka proved to be fundamentally different from that at Aransas, and returning yearlings usually left that area to find more suitable areas inland (Urbanek et al. 2010b; Fondow 2013).

As a result of our year-round monitoring of the reintroduced eastern migratory population since its inception and throughout its distribution, the current project database consists of census data for seasonal bird locations, associations, and reproduction with few missing values. These data have made possible the continuing study of methods, winter return, survival and mortality, migration movements, spring wandering movements, and reproduction. Reintroduction methods (costume-reared UL and DAR) have produced birds that survived to migrate, winter, and establish breeding territories in numbers needed to support establishment of a self-sustaining population; however, reproduction has been inadequate (Urbanek et al. 2010c, 2014; Converse et al. 2013). Objectives of this study are to 1) document changes in the winter distribution resulting from 11 y of releases through the winter of 2012, 2) identify the causes of these changes, and 3) assess implications of winter distribution to the outcome of the reintroduction. Knowledge and understanding of winter distribution is necessary for development of future research and management actions for this population. All whooping crane populations except the population at Aransas were extirpated before study on their wintering grounds was possible. Therefore, from a broader perspective, this study will also contribute to our understanding of whooping crane winter ecology in inland habitats and provide insight valuable to future restoration efforts.

Methods

Propagation, costume-rearing, and release sites

Sources of birds for this reintroduction were eggs from several captive propagation facilities, primarily Patuxent Wildlife Research Center, Laurel, Maryland; the International Crane Foundation, Baraboo, Wisconsin; and the Calgary Zoo, Calgary, Alberta. Some eggs were also obtained from nests abandoned by reintroduced whooping cranes in central Wisconsin (see below). All chicks were reared in isolation from human sights and sounds by caretakers in costume (Horwich 1989; Urbanek and Bookhout 1992; Figure 1). During the first decade, the core reintroduction area consisted of a large complex of shallow wetlands in Juneau and adjacent counties in central Wisconsin, including the specific rearing–release area on Necedah NWR (hereafter, Necedah; 44°04′N, 90°10′W). Releases in the core reintroduction area were discontinued after 2010 because of chronic widespread nest desertion apparently related to abundance of the black fly species Simulium annulus and Simulium johannseni (Urbanek et al. 2010c; Converse et al. 2013). Subsequent releases were made in eastern Wisconsin, where the black fly species implicated in the desertions were not prevalent.

Figure 1.

Costumed caretaker with whooping crane Grus americana juveniles for direct autumn release, Necedah National Wildlife Refuge, Wisconsin, October 2007 (photo by Danielle Reese, U.S. Fish and Wildlife Service).

Figure 1.

Costumed caretaker with whooping crane Grus americana juveniles for direct autumn release, Necedah National Wildlife Refuge, Wisconsin, October 2007 (photo by Danielle Reese, U.S. Fish and Wildlife Service).

Ultralight aircraft technique (UL)

Eggs for UL were hatched at Patuxent Wildlife Research Center, where the costume-reared chicks were initially trained to follow ultralight aircraft (Urbanek et al. 2010b). In 2001–2010 at age 30–70 d, the chicks were transferred to field facilities at Necedah for continued rearing, training, and to begin migration by previously described techniques (Lishman et al. 1997; Duff et al. 2001). Beginning in 2011, location of the field facility was changed and chicks were transferred to White River Marsh Wildlife Area (hereafter, White River Marsh; 43°54′N, 89°07′W), Green Lake County, eastern Wisconsin.

Staff of Operation Migration, Port Perry, Ontario, trained juveniles to follow ultralight aircraft and led them on their first autumn migration during each year (Figures 2 and 3). The primary release site was in salt marsh on Chassahowitzka (28°44′N, 82°39′W) on the central Gulf Coast of Florida. The initial route proceeded southbound and then southeasterly to central Indiana. There it intercepted the primary route used by the wild sandhill crane population (Toepfer and Crete 1979; McMillen 1988; Urbanek 1988) and continued to Florida. The major northern stopover for sandhill cranes at Jasper–Pulaski Fish and Wildlife Area (hereafter, Jasper–Pulaski) in northwestern Indiana was bypassed to avoid the airspace over the Chicago metropolitan area. Beginning with the 2008 migration, the original route through Indiana, east-central Kentucky and Tennessee, and Georgia was replaced with a more westerly route though Illinois, western Kentucky and Tennessee, and Alabama to minimize flying over mountainous terrain. In the winter that followed, a release site was added at St. Marks NWR (hereafter, St. Marks; 30°06′N, 84°17′W), Wakulla County, in the eastern Florida panhandle, to reduce risk of loss of an entire cohort due to a catastrophic event at a single site.

Figure 2.

Ultralight aircraft leading flock of juvenile costume-reared whooping cranes Grus americana from Necedah National Wildlife Refuge, Wisconsin, on autumn migration over southern Wisconsin, November 2009 (photo by Operation Migration).

Figure 2.

Ultralight aircraft leading flock of juvenile costume-reared whooping cranes Grus americana from Necedah National Wildlife Refuge, Wisconsin, on autumn migration over southern Wisconsin, November 2009 (photo by Operation Migration).

Figure 3.

Ultralight aircraft leading flock of juvenile costume-reared whooping cranes Grus americana from Necedah National Wildlife Refuge, Wisconsin, over northern Alabama, December 2010 (photo by Operation Migration).

Figure 3.

Ultralight aircraft leading flock of juvenile costume-reared whooping cranes Grus americana from Necedah National Wildlife Refuge, Wisconsin, over northern Alabama, December 2010 (photo by Operation Migration).

Both Chassahowitzka and St. Marks are in salt–brackish marsh habitats on the Gulf Coast. Black needlerush Juncus roemerianus was a dominant plant species, especially at Chassahowitzka. Release sites on both areas contained open-topped pens (1.6 ha and 1.1 ha, respectively, at Chassahowitzka and St. Marks) for the UL juveniles, were well-protected, and restricted to use only by project staff (Figure 4). At Chassahowitzka, surface access was possible only by airboat. Urbanek et al. (2010b) described pen design and management of birds at this site. With the exception of one bird, which was released offsite in 2007 after mortality of the remainder of its cohort (Spalding et al. 2010) and did not survive the winter, all of these birds were supplied with supplemental food. The supplemental feeding of released birds was only done at the juvenile release pens. The food encouraged the juveniles to roost in the predator-resistant pens at night. When necessary, costumed caretakers led the juveniles into the pen at dusk. At Chassahowitzka, the pen contained an artificial bar constructed of crushed oyster shells on top of an existing natural eastern oyster Crassostrea virginica bar in the tidal pool. The sloping sides provided roosting areas of suitable depths on most nights.

Figure 4.

Whooping cranes Grus americana in winter release pen on Chassahowitzka National Wildlife Refuge, Florida Gulf Coast, February 2006. Juveniles were led to this site from Necedah National Wildlife Refuge, Wisconsin, by ultralight aircraft (photo by Sara Zimorski, International Crane Foundation).

Figure 4.

Whooping cranes Grus americana in winter release pen on Chassahowitzka National Wildlife Refuge, Florida Gulf Coast, February 2006. Juveniles were led to this site from Necedah National Wildlife Refuge, Wisconsin, by ultralight aircraft (photo by Sara Zimorski, International Crane Foundation).

In 2011 the UL juveniles were led as far as Russellville, Franklin County, Alabama, and after a long ground delay associated with weather and permitting issues and resulting reluctance of birds to follow aircraft, the UL migration was terminated. The birds were then transported 70 km eastward by ground vehicle to winter on Wheeler NWR (hereafter, Wheeler; 34°33′N, 86°57′W), Morgan County, Alabama.

Direct autumn release (DAR)

During 2005–2010, eggs for DAR were hatched at the International Crane Foundation, and chicks were costume-reared there for 17–60 d. They were then transferred to Necedah, where they fledged. The DAR method depends on the association of the released juveniles with older whooping cranes or sandhill cranes to guide them on their first autumn migration. The juveniles were released in areas with older whooping cranes in October, just before migration (Urbanek et al. 2014). In 2011, the first year of shifting the reintroduction to eastern Wisconsin (see above), the DAR chicks were transferred from the International Crane Foundation to the field facility at Necedah to familiarize them with natural habitats. They were subsequently transported to Horicon NWR (hereafter, Horicon; 43°35′N, 88°38′W), Dodge County, eastern Wisconsin, at 83–102 d of age for later release.

Because they migrated during autumn on their own, three UL juveniles that were initially trained to follow ultralight aircraft are included among the DAR birds in this paper. As a result of earlier flight feather abnormalities that were subsequently resolved by feather regrowth, one bird in 2004 did not complete training in time to follow the ultralight-led migration. In 2008 a bird was removed from the UL flock because of aggression problems and inability to integrate into that flock. Both of these birds were later released on Necedah similar to DAR birds. In 2011 an UL juvenile escaped during a flight from White River Marsh, joined a large flock of sandhill cranes, and could not be recaptured. None of these birds were physically impaired when released, and although they were reared by UL protocols, they were considered suitable for addition to the population by the DAR method.

Tracking and monitoring

We individually marked all juveniles with colored leg bands and equipped them with leg-band-mounted very high frequency (VHF; 164–166 MHz) lithium battery transmitters (Advanced Telemetry Systems, Isanti, MN) before release. We also attached leg-band-mounted platform transmitter terminals (PTTs, i.e., satellite-monitored radios; Microwave Telemetry, Columbia, MD; North Star Science and Technology, King George, VA; Telonics, Mesa, AZ), to approximately three to six juveniles per year. As transmitters became nonfunctional, we recaptured whooping cranes, replaced VHF transmitters, and removed PTTs. We were able to capture the cranes by approaching them in costume and then either grabbing them by hand or using a drive trap (Wisconsin Department of Natural Resources 2006), leg noose (Folk et al. 2005), or Super Talon net gun (Advanced Weapons Technology, La Quinta, CA). We tracked cranes by conventional (VHF) telemetry with scanner receivers (Advanced Telemetry Systems; Telonics). We did most of this tracking from vehicles on the ground, and sometimes used Cessna aircraft, especially during migration and to search for temporarily missing birds. Each ground tracking vehicle was equipped with a through-the-roof (Melvin and Temple 1987), 7-element yagi antenna (Cushcraft Corporation, Manchester, NH).

A team of 3–4 trackers monitored released whooping cranes by VHF radiotelemetry throughout the annual cycle and geographic range of the cranes. Tracking efforts occurred daily, and individual trackers apportioned resources to cover as many birds as possible with priorities assigned to youngest birds or those with most variable movement patterns. Where access permitted, visual observations were made to document habitat and associations among whooping cranes and with sandhill cranes. Otherwise, locations were determined by triangulation. Coordinates were determined by plotting points on maps, usually at 200 m or finer resolution. Trackers used downloaded PTT data (CLS America, Lanham, MD) to identify distant search locations in areas not routinely covered by VHF tracking, and follow-up VHF tracking was performed at these sites as possible. We programmed PTT duty cycles to specifically identify roost locations and to maximize number of locations recorded for the youngest birds and birds during migration. Monitoring effort was also determined by logistics of personnel travel. For example, during winter we usually checked birds within 100 km of Chassahowitzka at least twice per week while other cranes were checked less frequently as resources permitted. In addition to tracking by project personnel, we often recruited cooperators to check birds at major wintering or migration areas. Members of the public also reported numerous sightings on the Whooping Crane Eastern Partnership (http://www.bringbackthecranes.org/) website or to project partners.

Data conventions and analyses

In this paper, we designated winters by the terminal year of the winter period (e.g., December 2001 through March 2002 is referenced as winter 2002). We identified wintering locations by roosting areas, which were usually discrete. However, the complex of ranchland in Pasco County, Florida, which was used mainly by subadults early in the project, was considered a single location even though at least four different ranches were involved. We defined breeding pairs as pairs in which nest building or copulation was documented or pairs that remained together for ≥1 y and held a breeding territory. Date of pair formation was the date that the members identified by these criteria first began associating consistently as a pair and not as part of a larger group. A few newly formed breeding pairs may have been missed because of insufficient observations to verify status. However, because of high monitoring intensity both from the ground and by air during the breeding season, we believe that all nests with eggs were located and hence all egg-producing pairs were identified.

We compared fidelity to wintering area by sex, release method (UL vs. DAR), and breeding status. In the latter analysis, nonbreeders included birds that were never paired or birds before they became members of a breeding pair. We considered birds to be breeders as soon as they became a member of a breeding pair, even if they later were not paired. We defined winter fidelity as inversely proportional to number of wintering locations over number of winters. We therefore calculated the mean number of final wintering locations per bird and the mean number of winters per bird for each group to be compared. If birds used more than one location in the same winter, we proportionally reduced the contribution of each location so that the total would equal one. The mean number of winters per bird differed between groups, and this would tend to cause a difference in the mean number of final locations (because this number could increase with age). Therefore, to standardize values, we regressed number of locations against number of winters for each group and then used the regression to calculate the estimated mean number of final locations for a group with mean number of winters equal to the average of the group-specific means. We used a second-order polynomial in all regressions. We then tested whether the adjusted means were different using a t-test. In the t-test, we used the population variances in the original sample. We used a significance value of 0.05 in all tests. We used a one-sample proportion test with continuity correction to determine effect of sex on selection of wintering area by newly formed pairs. We used Fisher's exact test to compare subsequent nest success of pairs wintering in different regions.

Results

Through winter 2012, 196 juveniles from 11 hatch-years (HY) were released into the population. Numbers by natal area consisted of 178 in central Wisconsin (HY2001–2010) and 18 in eastern Wisconsin (HY2011). Monitoring was particularly effective in the early years of the project, when the population was smaller and tracking effort was greater. Locations of few birds remained unknown during all or part of any winter. In winters 2003–2007, we located 99.4% of wintering cranes (n  =  172 bird-winters). We accounted for all project cranes, alive or dead, from 2001 through October 2007. In winters 2008–2011, we located 95.7% of cranes (n  =  301 bird-winters). We later verified the few missing birds as alive. Because of significantly reduced tracking effort per bird and a lapse in replacement of nonfunctional transmitters, we located only 86% of 100 cranes in winter 2012.

Ultralight aircraft-led cranes: first two winters and use of release sites

A total of 132 juveniles led by ultralight aircraft from Necedah to the Gulf Coast of Florida on their first autumn migration were released (110 on Chassahowitzka, winters 2002–2011; 22 on St. Marks, winters 2009–2011; Figure 5). In 2011 an additional nine juveniles were led by ultralight aircraft from White River Marsh, Green Lake County, Wisconsin, to northern Alabama and after a delay were transported by ground vehicle to Wheeler (winter 2012). All UL birds remained on these release areas during their first winter.

Figure 5.

First wintering locations of juvenile whooping cranes Grus americana released into the reintroduced population migrating between Wisconsin and southeastern United States, 2001–2012. Release sites of ultralight aircraft-led (UL) juveniles were Chassahowitzka, St. Marks, and Wheeler National Wildlife Refuges (NWR). Direct autumn release (DAR) birds consisted of 46 birds released on Necedah NWR, 8 DAR birds released on Horicon NWR, 3 juveniles originally trained for UL (ultralight-led migration) but then released or escaped in Wisconsin, and 3 wild-hatched juveniles (NAT) wintering with their parents. Also indicated are major sandhill crane G. canadensis stopover or wintering locations referred to in text.

Figure 5.

First wintering locations of juvenile whooping cranes Grus americana released into the reintroduced population migrating between Wisconsin and southeastern United States, 2001–2012. Release sites of ultralight aircraft-led (UL) juveniles were Chassahowitzka, St. Marks, and Wheeler National Wildlife Refuges (NWR). Direct autumn release (DAR) birds consisted of 46 birds released on Necedah NWR, 8 DAR birds released on Horicon NWR, 3 juveniles originally trained for UL (ultralight-led migration) but then released or escaped in Wisconsin, and 3 wild-hatched juveniles (NAT) wintering with their parents. Also indicated are major sandhill crane G. canadensis stopover or wintering locations referred to in text.

During their second winter, birds from the early UL releases on Chassahowitzka returned to the release site but remained only overnight or a few days before moving inland to freshwater wetlands. During 10 second winters, 68 (73.1%) of 93 surviving cranes that had been released on Chassahowitza wintered at inland sites in Florida or southern Georgia. Of those cranes, 42 wintered within 100 km of the release site, and 26 wintered at more remote sites as far distant as 260 km (Table 1; Tables S1–S3, Supplemental Material).

Table 1.

Numbers of whooping cranes Grus americana (WC) in locations or indicated categories during their second winter, reintroduced population migrating between Wisconsin and southeastern United States, 2003–2012. Release method or origin: UL  =  Ultralight-led, DAR  =  Direct autumn release, NAT  =  Natural reproduction. Chassahowitzka and St. Marks  =  National Wildlife Refuges, Gulf Coast of Florida.

Numbers of whooping cranes Grus americana (WC) in locations or indicated categories during their second winter, reintroduced population migrating between Wisconsin and southeastern United States, 2003–2012. Release method or origin: UL  =  Ultralight-led, DAR  =  Direct autumn release, NAT  =  Natural reproduction. Chassahowitzka and St. Marks  =  National Wildlife Refuges, Gulf Coast of Florida.
Numbers of whooping cranes Grus americana (WC) in locations or indicated categories during their second winter, reintroduced population migrating between Wisconsin and southeastern United States, 2003–2012. Release method or origin: UL  =  Ultralight-led, DAR  =  Direct autumn release, NAT  =  Natural reproduction. Chassahowitzka and St. Marks  =  National Wildlife Refuges, Gulf Coast of Florida.

Ten UL cranes of the HY2003 cohort wintered off the migration route in freshwater or slightly brackish wetlands near the Carolina coast during their second winter. These included three survivors of a group that migrated too far east of the autumn migration track during the previous spring and summered on the east side of Lake Michigan. Three others also encountered Lake Michigan and remained east of the lake in spring but found their way around the lake to Wisconsin during the summer. This group also migrated to the Carolinas in the autumn but then continued to Florida. Seven other members of the HY2003 cohort migrated to South Carolina to winter even though they had migrated directly to Wisconsin during the previous spring. No other cohort demonstrated this propensity to migrate to the Carolinas. In succeeding years most members of this cohort returned to the typical migration route, and no additional birds other than mates of HY2003 individuals wintered in coastal Carolina.

Although numerous returning individuals stopped briefly at Chassahowitzka, wintering of cranes 1 y of age or older on that area was limited. The latter individuals consisted of a territorial male and his female associates through several winters of the project period, and three subadults, each during parts of one winter only. All of these birds occupied the immediate area near the release pen-site, where they were attracted to the released juvenile cohort and associated supplemental food. The subadults joined the juvenile flock. The territorial male was aggressive and typically attempted to drive away juveniles and prevent them from feeding at the feeding station. Costumed caretakers alleviated this problem by using several management techniques, including establishment of additional feeding stations, spending more time with the birds while actively blocking the male from interacting with juveniles that were attempting to feed, and removal of feeders when caretakers were not present. Winter 2010 was the only winter in which an entire cohort (five returning yearlings plus a sixth bird, originally released at St. Marks) returned and remained to winter on Chassahowitzka away from the pen-site (Table 1). That winter had combined cold temperatures and high rainfall (Figure 6). This group also used marshes adjacent to uplands east of the release site in an area with little tidal effect, thus providing stable overnight water levels for roosting. Excepting cranes that were attracted to supplemental food and the juveniles at the release pen, only 1.0% of population bird-winters occurred at Chassahowitzka.

Figure 6.

Climatological conditions during the period of reintroduction of the whooping crane Grus americana population migrating between Wisconsin and southeastern United States, winters 2002–2012. Data are from December–February in each winter (National Climatic Data Center 2012). The Palmer Hydrological Drought Index (Palmer 1965) is based on precipitation, temperature, and associated parameters analyzed in a water-balance model to permit relative comparison of long-term hydrologic moisture conditions across space and time. Positive and negative values indicate water surplus and deficit, respectively.

Figure 6.

Climatological conditions during the period of reintroduction of the whooping crane Grus americana population migrating between Wisconsin and southeastern United States, winters 2002–2012. Data are from December–February in each winter (National Climatic Data Center 2012). The Palmer Hydrological Drought Index (Palmer 1965) is based on precipitation, temperature, and associated parameters analyzed in a water-balance model to permit relative comparison of long-term hydrologic moisture conditions across space and time. Positive and negative values indicate water surplus and deficit, respectively.

Unlike at Chassahowitzka, the first cohort (HY2008) released on St. Marks did not return to the release area the following winter but instead scattered widely within the range of the reintroduced whooping crane population. Of four survivors of that group, one wintered with whooping cranes, one wintered with sandhill cranes, and two wintered at large sandhill crane wintering areas that contained other whooping cranes. Some of the second St. Marks cohort (HY2009), however, followed the earlier pattern at Chassahowitzka, with confirmation of 5 of 10 birds returning to the release site before 4 birds moved inland to winter (Table 1). The fifth bird and an associate, which had been released at Chassahowitzka, were attracted to the juveniles and food at the pen and remained at the St. Marks release site during winter 2011. Of five birds in the HY2010 St. Marks cohort, none returned during their second winter (winter 2012); four wintered with other whooping cranes at widespread locations, and location of the fifth bird was undetermined. The second winter of birds that had been released at Wheeler in winter 2012 was beyond the period of study.

Direct autumn release: first two winters

A total of 46 individuals were released directly on Necedah during October of their hatch year (DAR). One UL juvenile escaped and migrated with sandhill cranes from White River Marsh to Florida. Eight juveniles were released according to DAR protocols during autumn on Horicon. Of 55 juveniles released in Wisconsin, 52 survived to begin their first migration according to varied scenarios. Including the 3 former UL birds that migrated unassisted from Wisconsin, 28 of the DAR juveniles began migration with older whooping cranes, 13 with sandhill cranes only, and 11 alone or only with other members of their cohort. Their resulting areas of first wintering were therefore widely dispersed through the migration and winter range of the population (Figure 5). More detailed results and methods, including interventions to correct errant migration, are described by Urbanek et al. (2014).

During their second winter many DAR birds migrated only to the Mid-South (Tennessee and northern Alabama; Table 1; Tables S1–S3, Supplemental Material). Many adult whooping cranes and sandhill cranes also wintered in that region, with Hiwassee Wildlife Refuge (hereafter, Hiwassee) on the Tennessee River in Meigs County, southeastern Tennessee, being a primary wintering area. Of 27 yearlings resulting from DAR juvenile releases during 6 y, wintering during the first and second winters, respectively, occurred mainly in the Mid-South, especially Tennessee (10 birds in that state each year). Ten yearlings returned to their previous wintering area in the second winter. During the second winter, seven yearlings wintered alone or with sandhill cranes.

Natural reproduction

Only three juveniles, all female, fledged in the population through 2011. All of these wild-hatched chicks migrated with their parents to Florida wintering territories on their first migration. During the second winter, one returned to the winter territory of her parents in Florida in winter 2008. Another yearling did not return to Florida but instead shortstopped (i.e., wintered north of the previous or traditional wintering area) in Indiana in winter 2012. This was, along with much of the population, in response to an unusually mild winter (Figure 6). The wintering location of the remaining yearling was not determined.

Chronology of the developing winter distribution

During the course of the project, wintering areas of the eastern population developed in four general regions: Florida–southern Georgia, Carolinas, Mid-South (mainly Tennessee and northern Alabama), and the North (Indiana, Illinois, and Kentucky; Figure 7). Reintroduced whooping cranes wintered at locations in Figure 8 according to the following chronology.

Figure 7.

Number of whooping cranes Grus americana wintering in four regions within the range of the reintroduced population migrating between Wisconsin and southeastern United States, winters 2002–2012. Birds originated from ultralight aircraft-led migration (UL), direct autumn release (DAR), and natural reproduction (NAT).

Figure 7.

Number of whooping cranes Grus americana wintering in four regions within the range of the reintroduced population migrating between Wisconsin and southeastern United States, winters 2002–2012. Birds originated from ultralight aircraft-led migration (UL), direct autumn release (DAR), and natural reproduction (NAT).

Figure 8.

Number of bird-winters and locations of free-ranging whooping cranes Grus americana within regions used by the reintroduced population migrating between Wisconsin and southeastern United States, winters 2003–2012. Bird-winters are apportioned to reflect period of use for birds wintering in more than one region in the same winter.

Figure 8.

Number of bird-winters and locations of free-ranging whooping cranes Grus americana within regions used by the reintroduced population migrating between Wisconsin and southeastern United States, winters 2003–2012. Bird-winters are apportioned to reflect period of use for birds wintering in more than one region in the same winter.

Figure 8.

Continued.

Figure 8.

Continued.

Figure 8.

Continued.

Figure 8.

Continued.

Initially, all birds returned to winter in Florida. A major wintering area of subadults developed on cattle ranches in Pasco County, 40–50 km southeast of the Chassahowitzka release site. Ten whooping cranes wintered on those ranches in winter 2004. Most of the HY2003 cohort did not return to Florida but instead wintered off the migration route in the Carolinas during their first unassisted winter. This pattern was not repeated by any subsequent cohort, and numbers declined in the Carolinas after that winter. In the same winter (2005), a female that was integrated with sandhill cranes (year-round) wintered with thousands of sandhill cranes at Hiwassee and a group of three whooping cranes also shortstopped to winter in Tennessee. In winter 2006, two of the first released DAR birds wintered with sandhill cranes at Hiwassee. Numbers of whooping cranes continued to increase there during the next several years. In winters 2006 and 2007, the population in Florida continued to grow as most UL birds returned to winter there.

The southeastern United States experienced high temperatures and extreme drought in winter 2007 (Figure 6). Along with drought in Wisconsin in 2006 and 2007, the mortality rate of the population nearly quadrupled (Urbanek et al. 2010a). In addition, a storm at the Chassahowitzka release site resulted in loss of the HY2006 cohort (Spalding et al. 2010). Many birds vacated the Pasco County ranches as habitat loss resulted from the drought and development pressures of a recent housing boom. Some birds began using a partially dewatered lake in a residential area 20 km southeast of Chassahowitzka. Proximity of humans, as well as some humans feeding birds, resulted in taming, which grew into additional problems of habituation to humans on the summering areas (Urbanek et al. 2014). A new major wintering area developed on Paynes Prairie Preserve State Park (100 km north-northeast of Chassahowitzka), Alachua County, as drought lowered normally higher water levels there to <30 cm in depth, resulting in more suitable area for roosting and foraging. Farther northward, one pair moved in response to drought to establish a territory on Wheeler, Alabama. Meanwhile, mild temperatures and high rainfall resulted in flooding of harvested cornfields in the river bottoms in Indiana (Figure 6) and wintering of whooping cranes began in the North.

The most significant changes in long-term winter distribution patterns occurred between winters 2007 and 2008 and between winters 2011 and 2012. With the increase in mortality rate of free-ranging birds in 2007 and loss of the HY2006 release cohort, the Florida–southern Georgia component of the population decreased almost two-fold in winter 2008. During winters 2008–2010, numbers of birds in the Mid-South increased as many birds of DAR origin (including some juveniles translocated after errant migration; Zimorski and Urbanek 2010) wintered at Hiwassee and older UL birds shortstopped after experiencing the drought on former Florida wintering areas. In winter 2011, numbers in Florida–southern Georgia rebounded as many younger UL birds returned, and lack of flooded habitat in Indiana slowed the growing number of birds attempting to winter there. However, winter 2012 was extremely short with mild temperatures (Figure 6); more than half of the located population shortstopped in Indiana, including a record 20 birds wintering on Goose Pond Fish and Wildlife Area (hereafter, Goose Pond), Greene County.

Associations with sandhill cranes

Of 753 whooping crane winter-locations (i.e., number of locations used during all winters for each whooping crane summed for all whooping cranes), 151 (20.1%) were on Chassahowitzka or St. Marks and contained no sandhill cranes, 225 others (29.9% at 53 locations) contained no sandhill cranes or only an occasional stray, 161 (21.4% at 34 locations) contained 2–100 sandhill cranes, and 216 (28.7% at 26 locations) were major sandhill crane wintering areas containing >100 to thousands of sandhill cranes (Tables S1 and S4, Supplemental Material). Whooping cranes and sandhill cranes often migrated together in autumn, and some whooping cranes found major crane wintering areas, such as Hiwassee, which contained up to 14,000 sandhill cranes (Aborn 2010), by this association. The two species also frequently wintered together. However, many of these associations were primarily co-occurrence in the same areas rather than integration into a single flock. At some locations, whooping cranes remained in wetlands during the day while sandhill cranes flew to feed in farm fields and only used the wetlands for roosting. In other instances whooping cranes flew with sandhill cranes to and from farm fields and foraged with them, but movements of whooping crane groups did not appear dependent on the sandhill cranes. Whooping cranes did not become integral members of sandhill crane flocks except for a few single unpaired birds that did not summer in the core reintroduction area. Most of these birds eventually disappeared, although three of these females did pair at 2–5 y of age with male whooping cranes. One male whooping crane in the first release cohort paired with a sandhill crane, a behavior never reported in natural populations of these two species. Sandhill cranes normally migrated 3–4 wk earlier than whooping cranes in spring, although some whooping cranes began migration with them, especially from Hiwassee.

Fidelity to wintering areas

For 136 birds with ≥2 y of wintering locations, mean number of wintering locations until death of the bird or through winter 2012 was 3.1 per bird. At 4.6 winters, the mean number of years of winter data per bird, regression of number of locations on number of winters for the population during the study period was 3.3 locations (Figure 9). Thus, winter site fidelity, which is the inverse of number of wintering locations over number of winters (see Methods for additional adjustments to data), was low for this population. Site fidelity was not significantly different between males and females (t134  =  −0.58, P  =  0.281) but was significantly greater for breeding birds than nonbreeders (t213 =  −2.79, P  =  0.003; Table 2; Table S5, Supplemental Material).

Figure 9.

Number of whooping crane Grus americana wintering locations as a function of number of winters, reintroduced population migrating between Wisconsin and southeastern United States, winters 2003–2012. Green dot  =  mean number of locations.

Figure 9.

Number of whooping crane Grus americana wintering locations as a function of number of winters, reintroduced population migrating between Wisconsin and southeastern United States, winters 2003–2012. Green dot  =  mean number of locations.

Table 2.

Wintering area fidelity of whooping cranes Grus americana, reintroduced population migrating between Wisconsin and southeastern United States, 2003–2012. Data are included for birds with known locations in two or more winters. HY  =  Hatch year, UL  =  Ultralight-led, DAR  =  Direct autumn release.

Wintering area fidelity of whooping cranes Grus americana, reintroduced population migrating between Wisconsin and southeastern United States, 2003–2012. Data are included for birds with known locations in two or more winters. HY  =  Hatch year, UL  =  Ultralight-led, DAR  =  Direct autumn release.
Wintering area fidelity of whooping cranes Grus americana, reintroduced population migrating between Wisconsin and southeastern United States, 2003–2012. Data are included for birds with known locations in two or more winters. HY  =  Hatch year, UL  =  Ultralight-led, DAR  =  Direct autumn release.

Fifty confirmed breeding pairs formed through winter 2012. With few exceptions for part of a winter, members of pairs always wintered together. At the end of winter 2012, 29 pairs were extant, including 1 already paired for 7 y. After pairing, females moved to the preceding wintering area of the male seven times more frequently than males to the previous area of the female (Z  =  2.75, n  =  16, P  =  0.006). However, nearly 50% of pairs selected a territory new to both (Table 3; Tables S2 and S6, Supplemental Material). Through winter 2012, 10 of 27 pairs (2–5 winters of data) always used the same winter territory after pairing, but overall fidelity was low, with number of wintering locations equal to approximately one-half of the number of winters (Table 4; Tables S2 and S6, Supplemental Material).

Table 3.

Location of the wintering area of whooping cranes Grus americana after pairing, reintroduced population migrating between Wisconsin and southeastern United States, 2005–2012. Wintering area was not located for two additional pairs.

Location of the wintering area of whooping cranes Grus americana after pairing, reintroduced population migrating between Wisconsin and southeastern United States, 2005–2012. Wintering area was not located for two additional pairs.
Location of the wintering area of whooping cranes Grus americana after pairing, reintroduced population migrating between Wisconsin and southeastern United States, 2005–2012. Wintering area was not located for two additional pairs.
Table 4.

Number of areas used per winter by whooping crane Grus americana breeding pairs with two or more winters together, reintroduced population migrating between Wisconsin and southeastern United States, 2003–2012.

Number of areas used per winter by whooping crane Grus americana breeding pairs with two or more winters together, reintroduced population migrating between Wisconsin and southeastern United States, 2003–2012.
Number of areas used per winter by whooping crane Grus americana breeding pairs with two or more winters together, reintroduced population migrating between Wisconsin and southeastern United States, 2003–2012.

Winter site fidelity was greater for DAR than UL birds in comparison to either all UL (t132  =  −2.31, P  =  0.011) or only UL birds during the same period as the DAR releases (≥2005; t87  =  −1.95, P  =  0.026; Table 2; Table S5, Supplemental Material). Addition of a few DAR juveniles to migrating groups of older UL birds appeared to have little effect on selection of wintering area by the older birds. However, in two cases in which a large group of DAR juveniles were associated with only one UL adult, the groups migrated southward successfully but wintered at locations not previously used by the adult. A UL male with four DAR juveniles wintered in Tennessee rather than his previous area in Florida. A UL male with seven DAR juveniles wintered at three different locations in the Mid-South during winter 2010. This was the only record of birds using more than two primary areas during the same winter.

Effects of winter distribution on mortality

Of 87 mortalities of released whooping cranes from the first release through winter 2012, 28 (32%) occurred late in autumn migration or during the winter on known wintering areas (Table 5; Tables S1 and S7, Supplemental Material). The two main causes of mortality were regionally specific. Predation, especially by bobcats Lynx rufus, accounted for most mortality in Florida. Gunshot or suspected gunshot was the primary cause of mortality along the migration route from southern Georgia through the Mid-South and North and accounted for 9 (75%) of those mortalities. With the exception of one bird shot during snow goose Chen caerulescens hunting, shootings appeared to be intentional vandalism. The only other recorded shooting of a whooping crane by the end of winter 2012 was also vandalism and occurred during the summer in Michigan.

Table 5.

Causes of mortality of whooping cranes Grus americana wintering in indicated regions, reintroduced population migrating between Wisconsin and southeastern United States, 2001–2012. Mortalities occurring late in autumn migration on known wintering areas are also included.

Causes of mortality of whooping cranes Grus americana wintering in indicated regions, reintroduced population migrating between Wisconsin and southeastern United States, 2001–2012. Mortalities occurring late in autumn migration on known wintering areas are also included.
Causes of mortality of whooping cranes Grus americana wintering in indicated regions, reintroduced population migrating between Wisconsin and southeastern United States, 2001–2012. Mortalities occurring late in autumn migration on known wintering areas are also included.

Effects of winter distribution on reproduction

Although some pairs later formed from associates that wintered together, no significant effect on pairing was apparent from the widespread winter distribution. Of 51 different breeding pairs formed through March 2012, including a pair formed just after completion of the spring migration in that month, 47 formed within the core reintroduction area in central Wisconsin, 2 in other areas of Wisconsin, and 2 during autumn migration or wintering on Hiwassee (Tennessee; Table S6, Supplemental Material).

There were no significant differences in subsequent nest success, as measured by full-term incubation, among regions in 2005–2011 (χ23  =  2.28, P  =  0.516) or in 2012 (χ23  =  1.62, P  =  0.654; Table 6; Tables S1 and S8, Supplemental Material). The North region had more successful pairs, but this was due to eight pairs that incubated full-term after wintering along with much of the population that shortstopped in Illinois, Indiana, or Kentucky during the unusually mild winter of 2012 (Figures 7 and 8). A partially successful experimental treatment to reduce numbers of black flies, previously implicated in nest abandonments, occurred coincidentally during the 2012 nesting season (WCEP 2014).

Table 6.

Number of whooping crane Grus americana pairs that incubated at least one nest full-term (30 d) during the breeding season after wintering in the indicated region during the preceding winter, reintroduced population migrating between Wisconsin and southeastern United States, 2005–2012. Two incubating pairs that abandoned the nest after human disturbance are excluded.

Number of whooping crane Grus americana pairs that incubated at least one nest full-term (30 d) during the breeding season after wintering in the indicated region during the preceding winter, reintroduced population migrating between Wisconsin and southeastern United States, 2005–2012. Two incubating pairs that abandoned the nest after human disturbance are excluded.
Number of whooping crane Grus americana pairs that incubated at least one nest full-term (30 d) during the breeding season after wintering in the indicated region during the preceding winter, reintroduced population migrating between Wisconsin and southeastern United States, 2005–2012. Two incubating pairs that abandoned the nest after human disturbance are excluded.

Discussion

Limitations of coastal salt marsh for wintering whooping cranes in Florida

A coastal site was selected as the initial winter release area for the eastern migratory whooping crane population to minimize contact with the reintroduced nonmigratory flock in Florida and provide habitat similar to that used by the natural population at Aransas NWR (hereafter, Aransas). Chassahowitzka supported abundant blue crabs Callinectes sapidus (Cannon 1998), which was the primary food item of whooping cranes on Aransas; but in other respects, habitat was fundamentally different (Urbanek et al. 2010b). A barrier island at Aransas protects the coastal marsh from tides and results in generally <3 cm change in overnight water levels at roost sites. Marsh vegetation consists mainly of low-growing species <30 cm in height. Salinity is highly variable, but freshwater sources are available within 1 km of the coastal marsh. The release site on Chassahowitzka, however, typically has variable wind-driven winter tides averaging a change of 30 cm overnight. The two substrates are soft muck and sharp oyster rock. Black needlerush forms dense stands >1 m in height. During most winters, water is near or beyond the salinity tolerance of whooping cranes, and there are no nearby sources of fresh water. Despite these disadvantages, this area has been very successful as a release site; older birds tend to winter elsewhere and thus minimize harassment of newly released juveniles. Birds can be protected from predation by roosting in the open-topped pen. These sites lack sandhill cranes, which could lead naïve juvenile whooping cranes into areas where they could be killed by predators or habituated to human activity. Release at the southern end of the migration route may also assist birds in learning familiarity with the landscape and in finding suitable inland wintering areas later. However, habitat for long-term year-to-year occupation only occurs inland, where fresh water is available and there are no tides to compromise roosting (Urbanek et al. 2010b; Fondow 2013). Except at the pen-site, where newly released UL juveniles and supplemental food acted as attractants, Chassahowitzka supported returning whooping cranes in only 1 of 10 winters. St. Marks, the coastal site added in 2009, has some freshwater impoundments, but like Chassahowitzka, no stable wintering areas away from the pen-site have developed at that coastal location either. In addition, fewer areas of suitable inland habitat occur in the vicinity of St. Marks.

Whooping cranes will drink water with salinity <23 parts per thousand (Hunt 1987). Salinities near the Chassahowitzka pen-site generally ranged from 17 to 25 parts per thousand (Urbanek et al. 2010b) and were too high to provide a good source of drinking water. Salinity decreased briefly only after heavy rains, and whooping cranes were largely dependent on fresh water artificially provided in a drinking receptacle. Whooping cranes overwintered on Chassahowitzka at a location other than the pen-site only during winter 2010, which was unusually cold with high precipitation and a temporary abatement of drought (Figure 6). These conditions resulted in salinities of 12 to 20 parts per thousand in the tidal salt marshes (R. P. Urbanek, unpublished data). Even lower salinities and roosting areas of sufficient depth also occurred in marshland adjacent to the uplands on the eastern shore of the refuge wetland during that winter.

Aransas is, with few exceptions, the single wintering location for the only natural surviving population of whooping cranes. The coastal prairies of Louisiana, high plateau wetlands of Mexico, and tidal marshes in South Carolina once supported this species in winter (Allen 1952). These historical winter distributions were more concentrated than the widely scattered distribution of current whooping cranes in the eastern migratory population. However, little or no information on habitat use is available for these extirpated populations. Unlike at Aransas, the fragmented nature of wintering habitat in Florida and lack of large blocks of protected habitat suitable for whooping cranes limit options for a single wintering area for the population. The widely dispersed winter range of the eastern migratory population, does, however, have an advantage over Aransas in that it reduces the possibility of loss of all birds due to a catastrophic event or to habitat degradation occurring at a single site. The latter is of great concern for the Aransas population because of lack of freshwater inflows due to drought and upstream human demands as well as loss of habitat to development and anticipated sea rise related to climate change (Stehn and Prieto 2010).

Factors influencing the resulting winter distribution

Habitat limitations of the predetermined coastal wintering area and the additional use of the DAR reintroduction technique, in which location of wintering area is variable, have resulted in a dynamic and widely dispersed winter distribution of the reintroduced population. Lacking a single large wintering area with suitable habitat (such as Aransas), where whooping cranes congregate as a result of homing and mutual attraction, UL birds first moved to multiple inland sites, thus already establishing the foundation for low fidelity to wintering areas. This lack of a core wintering area predisposed them to move to other wintering areas later as a result of other factors such as drought, habitat loss from land development in Florida, and natural tendencies to shortstop. Whooping cranes reintroduced by DAR methods demonstrated greater fidelity than those reintroduced by UL methods, but fidelity of DAR birds was also low and facilitated low winter site fidelity of the population. It should be noted that the fidelity index used assigned equal weight to each bird, whether there were 2 winters of data or 11. It was thus biased toward the younger birds. Because UL birds did not normally return to winter at their first winter release site, greater fidelity of DAR whooping cranes is unremarkable.

Winter 2007 was a turning point for the population because drought became extreme in the southeastern United States, particularly in Florida. Some previous wintering areas were abandoned. Wintering areas of the eastern population ultimately spread northward to include four general regions (Figures 7 and 8). Many key migration stopovers increasingly became used as wintering areas. These included Hiwassee (Tennessee), Wheeler (Alabama), Weiss Lake (Cherokee County, Alabama), Goose Pond (Indiana), and the area including Muscatatuck NWR and Ewing Bottoms (Jackson County, Indiana; Figure 5). Primary habitats used by reintroduced whooping cranes consisted of open shallow water and marsh, improved pasture (Florida only), and harvested cornfields (Fondow 2013). The next turning point occurred in winter 2012, which was extremely short and mild (Figure 6); more than half of the located population wintered in Indiana, including 20 birds at one site. Flexibility in choice of wintering location resulted in advantageous use of fields containing large quantities of waste corn in years when private lands in river bottoms were flooded or when mild temperatures provided suitable wetland conditions on managed state wildlife land in southern Indiana. Availability of food was, of course, important at all sites but not the main determinant of choice of winter region.

Different factors favored wintering in different regions. Region of release, specifically UL release at coastal sites; high rainfall; and frozen wetlands and snow in the North favored wintering of whooping cranes in Florida and southern Georgia. Region of release, especially of DAR birds; frozen wetlands and snow in the North; food-related shortstopping; and habitat loss to human disturbance and land development in Florida contributed to wintering in the Mid-South. Wintering in the North was related to high rainfall and resulting flooded bottomland cornfields; nonfreezing temperatures making food and roosting sites available (encouraging shortstopping); lack of site fidelity and tendency to shorten the migration route; tendency to continue use of shortstop areas in future winters; drought farther south; and habitat loss to human disturbance and land development in Florida. The wintering component on the Carolina coast was due to anomalous movements off the migration route, specifically of the HY2003 cohort, and was not repeated. The cause is not entirely understood. That segment of the population may ultimately disappear due to attrition.

Other factors affected winter distribution but did not necessarily favor wintering in a specific region. The tendency to develop a direct migration route (Mueller et al. 2013) resulted in a western track relative to the primary traditional sandhill crane migration route. Other factors included general associations with other cranes (flocking with large sandhill crane flocks or whooping cranes) and specific associations among whooping cranes (pairing, subadult groups). Local habitat conditions such as drought also contributed to changes in winter distributions within regions. Groups containing both DAR and UL birds tended to select winter sites new to both. DAR juveniles both followed and affected migration of older UL leaders. Few data are yet available on naturally produced young, but so far general behaviors of UL, DAR, and wild-reared whooping cranes have been similar, and birds from these different categories of origin have all fully integrated in the population.

Mortality

Mortality rate on wintering areas was similar to the overall annual rate including all areas of seasonal use. This pattern differs from that of the AWB population, in which greatest documented mortality occurred during migration (USFWS and CWS 2007). Of 50 carcasses of AWB whooping cranes recovered in 1950–2010, causes of death were power-line collision (20%), gunshot (20%), various other (36%), and unknown (24%), but 91% of dead birds were never found (Stehn and Haralson-Strobel 2014). Whooping cranes wintering in Florida were susceptible to risk of predation by bobcats. As on the breeding areas (Urbanek et al. 2010a), predation was most associated with drought. Loss of whooping cranes to shooting was significant and the most common cause of mortality north of Florida. Winter 2011 had the highest known or suspected loss to gunshot during the reintroduction, with the loss of four DAR juveniles and one adult UL male at two sites in Georgia and Alabama. Two additional birds were found shot in Indiana in winter 2012. In addition, this growing trend in loss of birds to shooting may be underestimated because of the simultaneous trends in reduced replacement of nonfunctional transmitters, reduced monitoring of the population, and resultant increase in number of missing birds with fate undetermined.

Reproduction

Most whooping cranes in the population paired by age 3–5 y (Urbanek et al. 2014). Although associations on wintering areas have contributed to pairing, few pairs have formed on the wintering areas. Therefore, the widespread winter distribution has not so far adversely affected pairing. However, the 2001–2010 cohorts completed their rearing period at Necedah and all migrated from the core reintroduction area of central Wisconsin. Their high rate of return to this large concentration of wetlands has facilitated pair formation and establishment of breeding territories (Urbanek et al. 2014). Beginning in 2011, in an attempt to avoid the chronic, systemic nest desertion (Urbanek et al. 2010c) in central Wisconsin, the focal point of the reintroduction was changed to eastern Wisconsin, where the black fly species implicated in the desertion are uncommon. The latter landscape is very different from central Wisconsin and consists of smaller wetlands scattered among intensive agriculture and a much larger human population. The effect of the resulting scattered distribution of adults on pair formation is not yet known, but if pair formation rate is lower than in central Wisconsin, the possible effect of winter distribution on pair formation and subsequent reproduction could become of greater concern.

Not unlike male-biased natal philopatry in cranes and most other nonanseriform birds (Greenwood 1980), male whooping cranes generally predominated over females in determining the wintering area of the pair, and breeding pairs exhibited more site fidelity than did nonbreeders. However, fidelity to winter territories was fundamentally different from that of the whooping crane flock wintering on Aransas, where pairs normally defend the same territory to which they return each year. Reintroduced eastern whooping cranes frequently changed wintering areas, and many wintered in groups with other whooping cranes. Preference for continued use of previously used wintering sites was frequently negated by changes in habitat suitability from winter to winter.

Winter habitat quality may be important to reproductive success in the AWB flock (Chavez-Ramirez 1996; Gil de Weir 2006); therefore, the winter distribution of whooping cranes in the eastern migratory population, as it relates to habitat quality, may be worthy of investigation. Although 109 nests with eggs have been produced from 2005 to 2012 (Urbanek et al. 2014; Whooping Crane Eastern Partnership, unpublished data), the high proportion of nest failures makes identification of relationships between wintering area and subsequent reproductive success difficult. Achievement of full-term incubation was greater for pairs that wintered in the North. However, this result appeared due to two coincident factors: 1) the large number of birds, including experienced pairs, that had shortstopped in that region in response to the mild winter of 2012 along with 2) a partially effective treatment of the black flies, which had been implicated in previous nest failures. No relationship between wintering area and reproduction was apparent, and therefore no conclusions can yet be drawn for this reintroduced population.

Management Implications

Lack of winter site fidelity by whooping cranes to areas in the southern part of the winter range supports the tendency to winter in the North. However, northern sites are only marginally or not suitable in severe winters because of frozen roost areas and snow covering food resources. Whooping cranes may need to move farther south within the same winter and may be reluctant to do so. Higher temperatures due to long-term climate change also favor wintering in the North, but more extremes in temperatures could make these areas unsuitable as stable wintering areas. In the southern areas, increased probability of drought may contribute to a continuing pattern of low site fidelity and changing winter distribution.

Public involvement in the project has been positive and significant, especially the response in reporting of sightings along the migration route. However, the species could benefit from expanded education. Habituation of whooping cranes to humans can result from frequent approach and especially from feeding. The resulting tameness is a contagious behavior that may contribute to reduced survival of these birds and their associates during other parts of the annual cycle. In some cases, it has been necessary to remove tame birds from the population and transfer them to captivity. Therefore, consistent with Whooping Crane Eastern Partnership guidelines, public viewing should be from no closer than 200 m. More critical is the growing problem of loss of birds to shooting, mostly as acts of vandalism. We believe that strict prosecution and penalties may reduce vandalism. We also believe that efforts to increase public appreciation and concern for whooping cranes would be beneficial along the migration route, especially in newly occupied wintering areas. Recently established hunting seasons for sandhill cranes in Kentucky and Tennessee pose additional risks but provide additional opportunity for public education.

Beginning in winter 2012, reduced tracking effort resulted in a large portion (14%) of locations remaining unknown for the wintering population. In addition, increasing numbers of birds have not been consistently monitored or have disappeared with fates never determined. Effective protection and management of the population depends on knowledge gained through monitoring. Efforts to resume and maintain more complete radiotracking of migrating and wintering birds could greatly benefit the reintroduction.

Any population of whooping cranes in the eastern United States will require management, consisting minimally of protection on the limited areas of preserved or restored wetland habitat in a landscape occupied by a large and growing human population. Much crane habitat, once abundant in central Florida, has already been and will continue to be lost to human encroachment. Much of the wetland habitat in regions north of Florida, though more limited, is protected on state and federal areas managed for wildlife. Continued consideration of whooping cranes in management of these lands may be critical to the welfare of this population.

The changing, widespread winter distribution of the eastern migratory population was not a planned or fully anticipated result of the reintroduction. The population and winter distribution remain in flux. Limited habitat, variability in climate among winters, and human encroachment will always result in some problems and remain areas of concern for the wintering population, especially while still in the reintroduction stage. However, the birds have used flexibility of movement to adapt to the available landscape, and current winter dynamics are compatible with successful establishment of the population. Problems limiting reproduction on the breeding area, on the other hand, must be solved before the population can be successful and should be the primary immediate focus of efforts to establish this population.

Supplemental Material

Please note: The Journal of Fish and Wildlife Management is not responsible for the content or functionality of any supplemental material. Queries should be directed to the corresponding author for the article.

Table S1. Description of field headings in Tables S2, S3, S4, S7, and S8.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S1 (11 KB XLSX).

Table S2. Wintering locations and group composition of whooping cranes Grus americana, reintroduced population migrating between Wisconsin and southeastern United States, 2002–2012. Per project policy to protect the cranes, locations of wintering areas are only specified to county level.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S2 (39 KB XLSX).

Table S3. Group composition of whooping cranes Grus americana, reintroduced population migrating between Wisconsin and southeastern United States, 2003–2012.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S3 (15 KB XLSX).

Table S4. Numbers of sandhill cranes Grus canadensis and number of whooping crane-winters (or partial winters) at wintering locations of whooping cranes Grus americana, reintroduced population migrating between Wisconsin and southeastern United States, winters 2003–2012.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S4 (19 KB XLSX).

Table S5. Release area, sex, breeding status, winter region, number of locations, group composition, and release method or origin of whooping cranes Grus americana, reintroduced population migrating between Wisconsin and southeastern United States, winters 2002–2012.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S5 (50 KB XLSX).

Table S6. Dates of pair formation or dissolution of whooping cranes Grus americana, reintroduced population migrating between Wisconsin and southeastern United States, 2004–2012.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S6 (15 KB XLSX).

Table S7. Date, location, and contributing factors to mortality of whooping cranes Grus americana, reintroduced population migrating between Wisconsin and southeastern United States, winters 2003–2012.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S7 (14 KB XLSX).

Table S8. Nest outcome, wintering areas, and winter regions of whooping cranes Grus americana, reintroduced population migrating between Wisconsin and southeastern United States, 2004–2012.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S8 (14 KB XLSX).

Reference S1. Cannon JR. 1998. Whooping crane wintering sites study. Report to Canadian–United States Whooping Crane Recovery Team, Calgary, Alberta.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S9 (4.1 MB PDF).

Reference S2. Chavez-Ramirez F. 1996. Food availability, foraging ecology, and energetics of whooping cranes wintering in Texas. Doctoral dissertation. College Station: Texas A&M University.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S10 (2.9 MB PDF).

Reference S3. Fondow LEA. 2013. Habitat selection of reintroduced migratory whooping cranes (Grus americana) on their wintering range. Master's thesis. Madison: University of Wisconsin.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S11 (1.4 MB PDF).

Reference S4. Gil de Weir K. 2006. Whooping crane (Grus americana) demography and environmental factors in a population growth simulation model. Doctoral dissertation. College Station: Texas A&M University.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S12 (2.4 MB PDF).

Reference S5. Hunt HE. 1987. The effects of burning and grazing on habitat use by whooping cranes and sandhill cranes on the Aransas National Wildlife Refuge, Texas. Doctoral dissertation. College Station: Texas A&M University.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S13 (6.2 MB PDF).

Reference S6. McMillen JL. 1988. Productivity and movements of the greater sandhill crane population at Seney National Wildlife Refuge: potential for an introduction of whooping cranes. Doctoral dissertation. Columbus: Ohio State University.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S14 (7.4 MB PDF).

Reference S7. Palmer WC. 1965. Meteorological drought. Washington, D.C.: NOAA Library and Information Services Division. U.S. Weather Bureau Research Paper 45.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S15 (5.8 MB PDF).

Reference S8. [USFWS] U.S. Fish and Wildlife Service and [CWS] Canadian Wildlife Service. 2007. International recovery plan for the whooping crane (Grus americana), third revision. U.S. Fish and Wildlife Service, Endangered Species Bulletins and Technical Reports Paper 45.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S16 (1.3 MB PDF).

Reference S9. Urbanek RP. 1988. Migration of sandhill cranes from the north shore of the North Channel of Lake Huron, Ontario. Columbus: Ohio Cooperative Fish and Wildlife Research Unit. Final report to Whooping Crane Coordinator, U.S. Fish and Wildlife Service, Albuquerque, New Mexico.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S17 (1.3 MB PDF).

Reference S10. Wisconsin Department of Natural Resources. 2006. Wisconsin whooping crane management plan. Madison: Wisconsin Department of Natural Resources PUBL-ER-650 06.

Found at DOI: http://dx.doi.org/10.3996/092012-JFWM-088.S18 (3.4 MB PDF).

Acknowledgments

This work is a product of the Whooping Crane Eastern Partnership, which was established in 1999 to reintroduce a migratory population of whooping cranes to eastern North America. The nine founding members are the Canada–U.S. Whooping Crane Recovery Team, U.S. Fish and Wildlife Service, USGS Patuxent Wildlife Research Center, USGS National Wildlife Health Center, Wisconsin Department of Natural Resources, Operation Migration, Inc., International Crane Foundation, National Fish and Wildlife Foundation, and the Natural Resources Foundation of Wisconsin. Many additional organizations and individuals have played an important role in the reintroduction, and the efforts of all participants are acknowledged as vital to the success of the project.

We thank all past tracking staff of the International Crane Foundation, especially L. Fondow, and numerous cooperators for monitoring free-ranging birds in the population. We especially thank the many International Crane Foundation and U.S. Fish and Wildlife Service interns who tracked released birds or assisted in rearing of direct autumn release chicks. We thank staffs of Patuxent Wildlife Research Center for rearing and Operation Migration for rearing, training, and leading migration of ultralight aircraft-led chicks; M. Wellington and International Crane Foundation staff for rearing direct autumn release chicks; T. Kohler and staff of Windway Capital Corporation for contributions and aircraft support; Florida Fish and Wildlife Conservation Commission and Wisconsin Department of Natural Resources for aircraft support; and Necedah, Chassahowitzka, St. Marks, and Wheeler National Wildlife Refuges, Crystal River Preserve State Park, Natural Resources Foundation of Wisconsin, U.S. Fish and Wildlife Service-Migratory Birds and State Programs, and Southwest Florida Water Management District for logistical support. Without the contributions of these and many others, this effort would not have been possible. We appreciate the assistance of J. Bart in data analysis, M. Balogh in map preparation, and D. Staller, J. Barzen, three anonymous reviewers, and the Subject Editor for comments on the manuscript.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Fish and Wildlife Service.

References

References
Aborn
DA
.
2010
.
Behavior and habitat use of greater sandhill cranes wintering in east Tennessee
.
Proceedings of the North American Crane Workshop
11
:
9
14
.
Allen
RP
.
1952
.
The whooping crane. Research Report 3
.
New York
:
National Audubon Society
.
Allen
RP
.
1956
.
A report on the whooping crane's northern breeding grounds. Supplement to Research Report 3
.
New York
:
National Audubon Society
.
Boyce
MS
.
1987
.
Time-series analysis and forecasting of the Aransas/Wood Buffalo whooping crane population
. Pages
1
9
in
Lewis
JC
,
editor
.
Proceedings 1985 crane workshop
.
Grand Island, Nebraska
:
Platte River Whooping Crane Maintenance Trust
. .
Cannon
JR
.
1998
.
Whooping crane wintering sites study
.
Report to Canadian–United States Whooping Crane Recovery Team, Calgary, Alberta
.
(see Supplemental Material, Reference S1, http://dx.doi.org/092012-JFWM-088.S9)
.
Chavez-Ramirez
F.
.
1996
.
Food availability, foraging ecology, and energetics of whooping cranes wintering in Texas. Doctoral dissertation
.
College Station
:
Texas A&M University
.
(see Supplemental Material, Reference S2, http://dx.doi.org/092012-JFWM-088.S10)
.
Converse
SJ
,
Royle
JA
,
Adler
PH
,
Urbanek
RP
,
Barzen
JA
.
2013
.
A hierarchical nest survival model integrating incomplete temporally varying covariates
.
Ecology and Evolution
3
:
4439
4447
.
Drewien
RC
,
Bizeau
EG
.
1977
.
Cross-fostering whooping cranes to sandhill crane foster-parents
. Pages
201
222
in
Temple
SA
,
editor
.
Endangered birds: management techniques for preserving threatening species
.
Madison
:
University of Wisconsin Press
.
Duff
JW
,
Lishman
WA
,
Clark
DA
,
Gee
GF
,
Ellis
DH
.
2001
.
Results of the first ultralight-led sandhill crane migration in eastern North America
.
Proceedings of the North American Crane Workshop
8
:
109
114
.
Ellis
DH
,
Lewis
JC
,
Gee
GF
,
Smith
DG
.
1992
.
Population recovery of the whooping crane with emphasis on reintroduction efforts: past and future
.
Proceedings of the North America Crane Workshop
6
:
142
150
.
Folk
MJ
,
Nesbitt
SA
,
Schwikert
ST
,
Schmidt
JA
,
Sullivan
KA
,
Miller
TJ
,
Baynes
SB
,
Parker
JM
.
2005
.
Techniques employed to capture whooping cranes in central Florida
.
Proceedings of the North American Crane Workshop
9
:
141
144
.
Folk
MJ
,
Rodgers
JA
Jr,
Dellinger
TA
,
Nesbitt
SA
,
Parker
JM
,
Spalding
MG
,
Baynes
SB
,
Chappell
MK
,
Schwikert
ST
.
2010
.
Status of non-migratory whooping cranes in Florida
.
Proceedings of the North American Crane Workshop
11
:
118
123
.
Fondow
LEA
.
2013
.
Habitat selection of reintroduced migratory whooping cranes (Grus americana) on their wintering range. Master's thesis
.
Madison
:
University of Wisconsin
.
(see Supplemental Material, Reference S3, http://dx.doi.org/092012-JFWM-088.S11)
.
Gil de Weir
K
.
2006
.
Whooping crane (Grus americana) demography and environmental factors in a population growth simulation model. Doctoral dissertation
.
College Station
:
Texas A&M University
.
(see Supplemental Material, Reference S4, http://dx.doi.org/092012-JFWM-088.S12)
.
Gomez
GM
.
1992
.
Whooping cranes in southwest Louisiana: history and human attitudes
.
Proceedings of the North American Crane Workshop
6
:
19
23
.
Gomez
GM
.
2014
.
The history and reintroduction of whooping cranes at White Lake Wetlands Conservation Area, Louisiana
.
Proceedings of the North American Crane Workshop
12
:
76
79
.
Greenwood
PJ
.
1980
.
Mating systems, philopatry and dispersal in birds and mammals
.
Animal Behaviour
28
:
1140
1162
.
Hjertaas
D
.
1994
.
Summer and breeding records of the whooping crane in Saskatchewan
.
Blue Jay
52
:
99
115
.
Horwich
RH
.
1989
.
Use of surrogate parental models and age periods in a successful release of hand-reared sandhill cranes
.
Zoo Biology
8
:
379
390
.
Hunt
HE
.
1987
.
The effects of burning and grazing on habitat use by whooping cranes and sandhill cranes on the Aransas National Wildlife Refuge, Texas. Doctoral dissertation
.
College Station
:
Texas A&M University
.
(see Supplemental Material, Reference S5, http://dx.doi.org/092012-JFWM-088.S13)
.
Lishman
WA
,
Teets
TL
,
Duff
JW
,
Sladen
WJL
,
Shire
GG
,
Goolsby
KM
,
Bezner Kerr
WA
,
Urbanek
RP
.
1997
.
A reintroduction technique for migratory birds: leading Canada geese and isolation-reared sandhill cranes with ultralight aircraft
.
Proceedings of the North American Crane Workshop
7
:
96
104
.
McMillen
JL
.
1988
.
Productivity and movements of the greater sandhill crane population at Seney National Wildlife Refuge: potential for an introduction of whooping cranes. Doctoral dissertation
.
Columbus
:
Ohio State University
.
(see Supplemental Material, Reference S6, http://dx.doi.org/092012-JFWM-088.S14)
.
Melvin
SM
,
Temple
SA
.
1987
.
Radio telemetry techniques for international crane studies
. Pages
481
492
in
Archibald
G
,
Pasquier
RF
,
editors
.
Proceedings of the 1983 international crane workshop
.
Baraboo, Wisconsin
:
International Crane Foundation
. .
Mueller
T
,
O'Hara
RB
,
Converse
SJ
,
Urbanek
RP
,
Fagan
WF
.
2013
.
Social learning of migratory performance
.
Science
341
:
999
1002
.
Nagendran
M
,
Urbanek
RP
,
Ellis
DH
.
1996
.
Special techniques, part D: reintroduction techniques
. Pages
231
240
in
Ellis
DH
,
Gee
GF
,
Mirande
CM
,
editors
.
Cranes: their biology, husbandry, and conservation
.
Washington, D.C
:
National Biological Service, U.S. Department of Interior, and Baraboo, Wisconsin: International Crane Foundation
.
National Climatic Data Center
.
2012
.
Plot time series
.
National Oceanic and Atmospheric Administration
. .
Palmer
WC
.
1965
.
Meteorological drought
.
Washington, D.C.
:
NOAA Library and Information Services Division. U.S. Weather Bureau Research Paper 45
(see Supplemental Material, Reference S7, http://dx.doi.org/092012-JFWM-088.S15); also available: http://www.wunderground.com/hurricane/2010/rwc/20100730/QC852U55no45.pdf (January 2014)
.
Spalding
MG
,
Terrell
S
,
Brooks
WB
.
2010
.
Pathology associated with lightning strike and drowning mortality of whooping cranes in Florida
.
Proceedings of the North American Crane Workshop
11
:
215
.
Stehn
TV
,
Haralson-Strobel
CL
.
2014
.
An update on mortality of fledged whooping cranes in the Aransas/Wood Buffalo population
.
Proceedings of the North American Crane Workshop
12
:
43
50
.
Stehn
TV
,
Prieto
F
.
2010
.
Changes in winter whooping crane territories and range 1950–2006
.
Proceedings of the North American Crane Workshop
11
:
40
56
.
Toepfer
JE
,
Crete
RA
.
1979
.
Migration of radio-tagged greater sandhill cranes from Minnesota and Wisconsin
. Pages
159
173
in
Lewis
JC
,
editor
.
Proceedings of the 1978 crane workshop
.
Fort Collins
:
Colorado State University Printing Service
. .
[ESA] U.S. Endangered Species Act of 1973, as amended, Pub. L. No. 93-205, 87 Stat. 884 (Dec. 28, 1973)
. .
[USFWS] U.S. Fish and Wildlife Service and [CWS] Canadian Wildlife Service
.
2007
.
International recovery plan for the whooping crane (Grus americana), third revision
.
U.S. Fish and Wildlife Service, Endangered Species Bulletins and Technical Reports Paper 45
. .
Urbanek
RP
.
1988
.
Migration of sandhill cranes from the north shore of the North Channel of Lake Huron, Ontario
.
Columbus
:
Ohio Cooperative Fish and Wildlife Research Unit. Final report to Whooping Crane Coordinator, U.S. Fish and Wildlife Service, Albuquerque, New Mexico
.
(see Supplemental Material, Reference S9, http://dx.doi.org/092012-JFWM-088.S17)
.
Urbanek
RP
,
Bookhout
TA
.
1992
.
Development of an isolation-rearing/gentle release procedure for reintroducing migratory cranes
.
Proceedings of the North American Crane Workshop
6
:
120
130
.
Urbanek
RP
,
Fondow
LEA
,
Zimorski
SE
.
2010a
.
Survival, reproduction, and movements of migratory whooping cranes during the first seven years of reintroduction
.
Proceedings of the North American Crane Workshop
11
:
124
132
.
Urbanek
RP
,
Fondow
LEA
,
Zimorski
SE
,
Wellington
MA
,
Nipper
MA
.
2010b
.
Winter release and management of reintroduced migratory whooping cranes Grus americana
.
Bird Conservation International
20
:
43
54
.
Urbanek
RP
,
Zimorski
SE
,
Fasoli
AM
,
Szyszkoski
EK
.
2010c
.
Nest desertion in a reintroduced population of migratory whooping cranes
.
Proceedings of the North American Crane Workshop
11
:
133
141
.
Urbanek
RP
,
Zimorski
SE
,
Szyszkoski
EK
,
Wellington
MA
.
2014
.
Ten-year status of the eastern migratory whooping crane reintroduction
.
Proceedings of the North American Crane Workshop
12
:
33
42
.
[WCEP] Whooping Crane Eastern Partnership
.
2014
.
Whooping crane nest productivity studies: black fly suppression study—Bti treatments
.
Whooping Crane Eastern Partnership
. .
Wisconsin Department of Natural Resources
.
2006
.
Wisconsin whooping crane management plan
.
Madison
:
Wisconsin Department of Natural Resources PUBL-ER-650 06
.
(see Supplemental Material, Reference S10, http://dx.doi.org/092012-JFWM-088.S18)
.
Zimorski
SE
,
Urbanek
RP
.
2010
.
The role of retrieval and translocation in a reintroduced population of migratory whooping cranes
.
Proceedings of the North American Crane Workshop
11
:
216
.

Author notes

Urbanek RP, Szyszkoski EK, Zimorski SE. 2014. Winter distribution dynamics and implications to a reintroduced population of migratory whooping cranes. Journal of Fish and Wildlife Management 5(2):340–362; e1944-687X. doi: 10.3996/092012-JFWM-088

The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service.