Novel ecosystems arise for a variety of reasons, most notably from the introduction of nonnative species. Understanding the interactions between traditional habitats, novel habitats, and species of conservation interest is important when planning successful conservation strategies. In the United States, the snail kite Rostrhamus sociabilis plumbeus is a federally endangered species whose population in Florida has undergone declines within the past decade. While studying the foraging behavior of breeding snail kites on Lake Tohopekaliga (Lake Toho), we discovered the unexpected use of disturbed ephemeral wetlands adjacent to the lake. These wetlands represent a novel habitat for snail kites; they would not have been viable foraging areas prior to the introduction of the exotic island apple snail Pomacea maculata. By examining the differences between snail kite behavior in traditional and novel habitats, we were able to identify some characteristics of novel habitats that may be important in determining their value to snail kites. The novel wetland areas were highly attractive to snail kites, likely because of the high snail capture rates. The survival of snail kite nests occurring within the novel areas appeared to be similar to that of nests occurring in more traditional, nearby areas on Lake Toho. However, whether or not snail kites used novel habitats as nesting areas appeared to be dependent upon water depth and availability of nesting substrate within these areas. The snail kites' dynamic use of the novel habitat demonstrates both the value of a novel ecosystem and the importance of traditional habitats to a species of conservation concern.

Novel ecosystems are assemblages of species that have not previously occurred in a given biome and may arise for a variety of reasons, including land-use changes, climatic variation, and the introduction of nonnative species (Hobbs et al. 2006, 2009). Given the increasing frequency with which habitats are being altered and invasive species are being introduced, the interaction of novel ecosystems and imperiled species merits consideration when planning conservation strategies. Novel ecosystems can have a variety of positive and negative effects on the organisms existing within and adjacent to them (Pyšek et al. 2012; Simberloff et al. 2013; Rogers and Chown 2014; Cattau et al. 2016), and may even allow for the restoration of imperiled species (Zavaleta et al. 2001; Foster and Robinson 2007). Here, we examine the value of a novel ecosystem to the snail kite Rostrhamus sociabilis plumbeus in Florida, which is listed as endangered pursuant to the U.S. Endangered Species Act (ESA 1973, as amended; Federal Register 1967, 2007).

Historically, a single species of native apple snail existed in Florida wetlands, the Florida apple snail Pomacea paludosa. However, as early as 2001, the island apple snail Pomacea maculata, native to South America (Rawlings et al. 2007), was introduced to Lake Tohopekaliga (Lake Toho). Lake Toho is a lake within the Kissimmee Chain of Lakes in central Florida. The lake is approximately 8,176 ha in area with an average depth of 2.1 m at its highest regulated stage (55.0 National Geodetic Vertical Datum ft). It is eutrophic, and approximately 25% of its area consists of emergent littoral vegetation (HDR Engineering Inc. 1989). By 2006 the island apple snail had become more abundant than the native Florida apple snail throughout Lake Toho (Desa 2008). Although within the same genus, the two species of snail differ notably in size, diet, fecundity, and environmental tolerances. The nonnative island apple snail is larger, more tolerant of drought, can survive on a broader range of food resources, has a longer life span, and is more fecund (Table 1; Perry 1974; Turner 1996; Sharfstein and Steinman 2001; Estebenet and Martin 2002; Ramakrishnan 2007; Barnes et al. 2008; Darby et al. 2008; Morrison and Hay 2011). Thus the island apple snail represents a novel addition to the wetland ecosystems of Florida, which is causing pervasive ecosystem-level effects. The introduction of the island apple snail affects a wide variety of flora and fauna both in its role as a voracious herbivore and as a desirable prey item. The island apple snail consumes large amounts of vegetation biomass and has adversely affected both agricultural and natural wetlands by completely denuding them of vegetation (Rawlings et al. 2007; Baker et al. 2010; Burlakova et al. 2010). The island apple snail has also become a common prey item for a variety of species, including American alligators Alligator mississippiensis (personal observation), limpkins Aramus guarauna (personal observation), and the endangered, highly specialized snail kite (Cattau et al. 2010; Fletcher et al. 2015). Prior to the introduction of the island apple snail, the snail kite had subsisted almost exclusively on the Florida apple snail (Sykes 1987b; Sykes et al. 1995).

Table 1.

Life history traits of the Florida apple snail Pomacea paludosa and island apple snail Pomacea maculata relevant to each species' role as a food resource for snail kites Rostrhamus sociabilis plumbeus in Florida.

Life history traits of the Florida apple snail Pomacea paludosa and island apple snail Pomacea maculata relevant to each species' role as a food resource for snail kites Rostrhamus sociabilis plumbeus in Florida.
Life history traits of the Florida apple snail Pomacea paludosa and island apple snail Pomacea maculata relevant to each species' role as a food resource for snail kites Rostrhamus sociabilis plumbeus in Florida.

The snail kite population decreased from approximately 3,400 individuals statewide in 1999 to between 700 and 800 individuals in 2008 and 2009 (Reichert et al. 2011; Fletcher et al. 2015). During the time of this study, the breeding snail kite population became heavily concentrated on the Kissimmee Chain of Lakes, (particularly on Lake Toho; Reichert et al. 2011), although more recently the distribution has become more even throughout the range and snail kite numbers have risen to approximately 1,800 individuals (Fletcher et al. 2015). The recent normalization of the snail kite's breeding range and population increases appear to be correlated with the expanding presence of island apple snails in Florida wetlands (Fletcher et al. 2015; Cattau et al. 2016).

In the course of identifying key snail kite foraging areas on Lake Toho, we found that snail kites were foraging and building nests in previously undocumented areas, namely wetlands adjacent to the main body of the lake with no direct hydrologic connection to any major natural water bodies. Given the intensive nature of snail kite surveys that have occurred on this lake since 1995 (Reichert et al. 2011), it unlikely that snail kite use of these wetlands was previously overlooked, but rather that snail kite use of these areas represents a recent change in habitat use. These areas included impounded cattle pastures, drainage ditches, storm-water retention ponds, and man-made mitigation wetlands. Although varied in form, these areas were all eutrophic with hydroperiods that varied drastically with rainfall.

The Florida apple snail's relatively restricted diet (Sharfstein and Steinman 2001; Morrison and Hay 2011) and reduced survival in dry conditions (Darby et al. 2003, 2004, 2008; Ramakrishnan 2007), likely prevent it from surviving in disturbed areas with unstable hydroperiods. No evidence of Florida apple snails (live snails, shells, or eggs) was observed in any of the novel wetland areas during the course of this study. Therefore, it is likely the invasion of the island apple snail, which can readily colonize such wetlands and has been documented to do so in great abundances (Burlakova et al. 2010), that made these areas amenable to snail kite use. These off-lake wetlands are novel habitat for snail kites because the recent invasion of the island apple snail has made them suitable for snail kite use. Similar responses by snail kites to a recent invasion of apple snails previously have been observed in Panama and Ecuador (Angehr 1999; Horgan et al. 2014). Although the novel wetlands could possibly prove to be valuable foraging grounds, the unstable water levels within the novel areas could expose any snail kite nesting attempts to terrestrial predators. The island apple snail will likely continue its spread throughout Florida's wetlands; therefore, it is vital to the snail kites' range-wide conservation that we understand how they are using these novel areas and novel food source.

To assess the value of these novel wetland areas to snail kites, we compared foraging behavior, snail capture rates, nest density, and nest survival between off-lake wetlands and traditional lake habitat. We expected that snail kites foraging in off-lake wetlands would have higher snail capture rates and that off-lake wetlands would contain higher nest densities, but lower nest success.

To ensure that individual snail kites could be repeatedly located, we conducted observations primarily on snail kites affixed with radiotransmitters. We trapped snail kites on Lake Toho using aquatic bal-chatri traps (Mahoney et al. 2010) and affixed them with very high frequency radiotransmitters. We conducted trapping from January 2009 through February 2011, during both breeding and nonbreeding seasons. We captured only nonbreeding snail kites or snail kites that were tending nests with eggs or nestlings; we avoided snail kites that were in the building stage of nesting to reduce the potential of disrupting the nesting attempt. We monitored the shore of Lake Toho monthly by airboat using a scanning radio receiver and Yagi antenna during the snail kite breeding seasons (January–August) of 2010 and 2011. We located all radiomarked snail kites and noted their breeding status. Once we located a breeding radiomarked snail kite, we revisited it every 2–4 d. We observed each breeding snail kite for approximately 1 h from a distance of ≤500 m using binoculars and a spotting scope. Observations occurred between the hours of sunrise and 1300 hours and between 1500 hours and sunset, corresponding to the hours of greatest snail kite activity (Snyder and Snyder 1969; Sykes 1987b).

During observations, we noted the start and end times of foraging bouts to the nearest second. Foraging bouts started when a snail kite left its perch and ended when a kite successfully captured a snail or returned to a perch. We recorded the total amount of flight time within each foraging bout, as well as whether or not a snail was captured within the bout. We defined a capture as any time a snail kite fully removed a snail from the water (Figure 1). We took locations of all captures using a Global Positioning System (GPS). We defined a foraging bout as off-lake if it occurred over a wetland with no direct hydrologic connection to Lake Toho. Additionally, we classified each foraging bout as either a course hunting bout or a perch hunting bout. Course hunting involves the snail kite searching for snails while flying slowly and low (1.5–10 m) over the water (Sykes et al. 1995). Perch hunting involves the snail kite visually searching for snails in the immediate surrounding habitat while remaining perched. When a snail is located, the snail kite will fly directly to retrieve the snail.

Figure 1.

A snail kite Rostrhamus sociabilis plumbeus successfully capturing an island apple snail Pomacea maculata from submerged aquatic vegetation on Lake Tohopekaliga in Florida in 2011. This sequence demonstrates an example of the foraging behavior observed during a foraging study of snail kites on Lake Tohopekaliga in 2010 and 2011.

Figure 1.

A snail kite Rostrhamus sociabilis plumbeus successfully capturing an island apple snail Pomacea maculata from submerged aquatic vegetation on Lake Tohopekaliga in Florida in 2011. This sequence demonstrates an example of the foraging behavior observed during a foraging study of snail kites on Lake Tohopekaliga in 2010 and 2011.

Close modal

We continued observations of breeding snail kites until the nest failed, succeeded (we considered a nest successful when the young reached 30 d old), or the adult stopped tending the nest (occasionally snail kites will desert a nest to the care of the other adult; Sykes 1987c; Olbert 2013). We stopped observations in instances where the observer's presence appeared to be disturbing or influencing the behavior of the nesting snail kites (as indicated by defensive calling, lack of food delivery to nestlings, or prolonged periods of inactivity).

In addition to observations on individual breeding snail kites, we made attempts to locate all snail kite nests on the lake during the course of annual population monitoring surveys. From January through September, we surveyed the lake intensely by airboat approximately every 20 d (Reichert et al. 2011). In the course of these surveys, when any snail kite was observed displaying breeding behavior (defensive calling, food or stick carrying, copulation, or aerial displays), we attempted to locate the snail kite nest. Estimates show that we were able to locate approximately 65% of all nests on lakes (Fletcher et al. 2015). Once we located a nest, we located its GPS location and checked it on every subsequent survey until it either failed or successfully fledged young. At each nest check, we took water depth measurements underneath the nest.

To determine whether off-lake areas provided snail kites with enhanced foraging opportunities, we compared the probability that a snail kite would catch a snail during a foraging bout that occurred off-lake with those bouts that occurred over the main body of Lake Toho using a Generalized Linear Mixed Model (SAS Institute Inc. 1989). The response variable was whether or not a capture occurred during a bout. We used year and foraging area (on-lake 2010, off-lake 2010, on-lake 2011, off-lake 2011) as the predictor variable. We ran the model with a binomial distribution, a logit link, and the total flight time within each bout as an offset variable. We used individual bird as a random effect to account for individual variation in foraging ability (Tables S1, S2, Supplemental Material). Significance for this test was determined at α = 0.05.

To determine whether snail kites used different foraging techniques in on- and off-lake wetlands, we compared the probability that a snail kite would utilize perch hunting strategies during an off-lake foraging bout with those bouts that occurred over the main body of Lake Toho using a Generalized Linear Mixed Model (SAS Institute Inc. 1989). The response variable used was whether or not a bout employed perch hunting, and the year and foraging area (on-lake 2010, off-lake 2010, on-lake 2011, and off-lake 2011) was the predictor variable (Table S2, Supplemental Material). The same model structure was used as the above described model (without an offset variable).

For each year, we created a density map of the snail kite nests on the lake using the point density tool in ArcGIS 9.3. We calculated the density estimates using the same search radius (5-cell search radius on a 50-m raster) for both years so that the spatial variation in nest density between years could be compared. We then measured the distance between the two highest value cells in each year's raster.

We compared the daily survival rates of snail kite nests occurring off the main body of the lake with those occurring on Lake Toho using Shaffer's logistic exposure method (Shaffer and Burger 2004). For this analysis, we used the year and nesting area (on-lake 2010, off-lake 2010, and on-lake 2011) as the predictor variable (Tables S1, S3, Supplemental Material). We determined significance for this test at α = 0.05.

We captured 24 adult snail kites on Lake Toho between January 2009 and February 2011. In addition to snail kites captured as adults, we monitored six snail kites that had been radiotagged as nestlings in previous years and were observed exhibiting breeding behavior during the study period. This resulted in 27 total snail kites being monitored in 2010, and 25 in 2011. Observations of these snail kites resulted in foraging bouts being observed from 19 individuals, 13 in 2010 and 13 in 2011. In total, we observed 500 foraging bouts, 154 in 2010 and 346 in 2011.

Between the two years, the monitored snail kites used five off-lake wetlands (three in 2010, three in 2011; Figure 2). Only one off-lake wetland, Shingle Marsh, was used by snail kites as a nesting area, primarily in 2010. In 2010, we found 17 snail kite nests (28% of all initiated nests) within Shingle Marsh, whereas in 2011, we found only two (3% of all initiated nests) in the same area. In 2010, 23% of the observed snail kites foraged exclusively in off-lake areas, 23% foraged in a mix of on- and off-lake areas, and 54% foraged exclusively on the lake. In 2011, the percentage of snail kites foraging in off-lake areas, a mix of off- and on-lake areas, and on-lake was 8%, 23%, and 69% respectively.

Figure 2.

Lake Tohopekaliga and surrounding areas, located in central Florida. This lake was the site of a foraging study of snail kites Rostrhamus sociabilis plumbeus in 2010 and 2011. The main body of the lake is indicated in blue. Purple areas indicate the locations of novel off-lake foraging areas used by snail kites during the study. Area A (Shingle Marsh) was used by snail kites in 2010 and 2011, and was the only off-lake area in which snail kites nested. Areas B and C were only used in 2011 and areas D and E were only used in 2010.

Figure 2.

Lake Tohopekaliga and surrounding areas, located in central Florida. This lake was the site of a foraging study of snail kites Rostrhamus sociabilis plumbeus in 2010 and 2011. The main body of the lake is indicated in blue. Purple areas indicate the locations of novel off-lake foraging areas used by snail kites during the study. Area A (Shingle Marsh) was used by snail kites in 2010 and 2011, and was the only off-lake area in which snail kites nested. Areas B and C were only used in 2011 and areas D and E were only used in 2010.

Close modal

Snail kites foraging over off-lake wetlands differed in both their foraging success rates and foraging behavior from snail kites foraging on the main body of the lake. Foraging bouts in both years that occurred over off-lake wetlands were significantly more likely to result in a snail capture than those that occurred over the main body of the lake (ddf = 478; 2010: t = 2.67, P = 0.008; 2011: t = 4.56, P < 0.0001; Figure 3A). Foraging bouts in both years that occurred over off-lake wetlands were significantly more likely to be perch hunting bouts than course hunting bouts (ddf = 478; 2010: t = 4.74, P < 0.0001; 2011: t = 5.74, P < 0.0001; Figure 3B).

Figure 3.

Comparison of foraging success and foraging behavior of snail kites Rostrhamus sociabilis plumbeus in different wetland types on and around Lake Tohopekaliga in Florida in 2010 and 2011. (A) The snail capture probabilities and 95% confidence intervals of snail kites primarily foraging in novel off-lake wetlands versus those foraging in traditional on-lake foraging areas in 2010 and 2011. (B) The probability and 95% confidence intervals of a snail kite perch hunting in off-lake wetlands versus on-lake wetlands in 2010 and 2011. Estimates were derived from a generalized linear mixed model with a binomial distribution and a logit link. Individual bird was used as a random effect to account for variation in individual foraging ability.

Figure 3.

Comparison of foraging success and foraging behavior of snail kites Rostrhamus sociabilis plumbeus in different wetland types on and around Lake Tohopekaliga in Florida in 2010 and 2011. (A) The snail capture probabilities and 95% confidence intervals of snail kites primarily foraging in novel off-lake wetlands versus those foraging in traditional on-lake foraging areas in 2010 and 2011. (B) The probability and 95% confidence intervals of a snail kite perch hunting in off-lake wetlands versus on-lake wetlands in 2010 and 2011. Estimates were derived from a generalized linear mixed model with a binomial distribution and a logit link. Individual bird was used as a random effect to account for variation in individual foraging ability.

Close modal

In 2010, we found 63 initiated snail kite nests (nests in which eggs had been laid) on and adjacent to Lake Toho; and in 2011, we found 79 nests. We used these nests both in the nest density and daily survival rate calculations. We removed nests with unknown fates from the daily survival rate analysis, resulting in 53 nests from 2010 and 71 nests from 2011 being analyzed. Daily nest survival was significantly higher in nests occurring on the main body of Lake Toho in 2011 (0.987 ± 0.002) than those occurring in the one off-lake wetland (0.973 ± 0.007), Shingle Marsh, used by snail kites as a nesting site in 2010 (ddf = 522, z = −2.28, P = 0.022). However, nests that occurred on Lake Toho in 2010 (0.981 ± 0.003) had similar survival to both on-lake 2011 nests and Shingle Marsh 2010 nests (ddf = 522; 2010: z = −1.04, P = 0.296; 2011: z = −1.53, P = 0.125; Figure 4).

Figure 4.

Comparison of daily nest survival rates of snail kites Rostrhamus sociabilis plumbeus nesting in different wetland types on and around Lake Tohopekaliga in Florida in 2010 and 2011. This chart displays daily nest survival estimates and 95% CI of snail kite nests located in novel off-lake wetlands and those located on Lake Tohopekaliga by year. The number of snail kites nesting off-lake in 2011 was too small (n = 2) to estimate daily survival rates. Daily survival-rate estimates were derived from a logistic exposure model. Snail kite nests were located and monitored as part of a concurrent snail kite demography monitoring project run by the Florida Cooperative Fish and Wildlife Research Unit.

Figure 4.

Comparison of daily nest survival rates of snail kites Rostrhamus sociabilis plumbeus nesting in different wetland types on and around Lake Tohopekaliga in Florida in 2010 and 2011. This chart displays daily nest survival estimates and 95% CI of snail kite nests located in novel off-lake wetlands and those located on Lake Tohopekaliga by year. The number of snail kites nesting off-lake in 2011 was too small (n = 2) to estimate daily survival rates. Daily survival-rate estimates were derived from a logistic exposure model. Snail kite nests were located and monitored as part of a concurrent snail kite demography monitoring project run by the Florida Cooperative Fish and Wildlife Research Unit.

Close modal

In 2010, the area with the highest density of snail kite nests was in Shingle Marsh, with a density of 9.2 nests/10 km2. The next densest cell had a density of 3.6 nests/10 km2 and was located approximately 3.3 km away from Shingle Marsh on the main body of Lake Toho. In 2011, the area with the highest density of snail kite nests occurred immediately adjacent to Shingle Marsh on the main body of Lake Toho, with 4.6 nests/10 km2. The next densest cell had a density of 3.6 nests/10 km2 and occurred at a nesting site approximately 4.7 km away (Figure 5).

Figure 5.

Density of snail kite Rostrhamus sociabilis plumbeus nests on Lake Tohopekaliga, Florida, in (A) 2010 and (B) 2011. In both years, the densest cluster of nests was located either in or adjacent to an off-lake wetland found to be heavily used by snail kites during a foraging study. Snail kite nests were located and monitored as part of a concurrent snail kite demography monitoring project run by the Florida Cooperative Fish and Wildlife Research Unit.

Figure 5.

Density of snail kite Rostrhamus sociabilis plumbeus nests on Lake Tohopekaliga, Florida, in (A) 2010 and (B) 2011. In both years, the densest cluster of nests was located either in or adjacent to an off-lake wetland found to be heavily used by snail kites during a foraging study. Snail kite nests were located and monitored as part of a concurrent snail kite demography monitoring project run by the Florida Cooperative Fish and Wildlife Research Unit.

Close modal

As the invasive island apple snail continues to spread across Florida, snail kites will likely expand their use of novel habitats (Fletcher et al. 2015; Cattau et al. 2016). By examining the mechanisms behind the dynamics of snail kite behavior in traditional and novel habitats, we are able to identify some characteristics of novel habitats that may be important in determining the habitat's value to snail kites. Furthermore, we highlight the inherent complexity of the addition of novel species to an ecosystem, with a wide variety of effects on native species.

It is important to note that the dominant snail species in both the main body of the lake and the off-lake wetland areas was the island apple snail. Rather than a difference in prey species, the observed differences in snail kite foraging rates and foraging behavior are likely related to physical differences in the two wetland types. The physical characteristics could impact snail kite foraging directly by offering a physically different landscape, or indirectly, by altering prey densities.

There are a variety of processes that may account for increased snail densities in off-lake wetlands and thus increased snail capture rates. These processes include the increased productivity of impounded wetlands (HDR Engineering Inc. 1989; Richardson et al. 1990; Gathumbi et al. 2005) and the lack of aquatic snail predators in ephemeral wetlands (Snyder and Snyder 1971). Indeed, similar ephemeral eutrophic wetlands in Texas have demonstrated elevated island apple snail densities (Burlakova et al. 2010).

In addition to snail densities, differences in vegetation structure may also be driving differences in snail capture rates. Snails only become available to foraging snail kites within 15 cm of the water's surface as they climb emergent vegetation to breathe and/or lay eggs at the water's surface (Thiengo 1987; Turner 1996; Ramakrishnan 2007; Seuffert and Martín 2010). All of the off-lake wetlands being used by snail kites consisted of very little open water, instead being filled with a variety of vegetation (Luziola fluitans, Polygynum spp.) that provided the structure necessary to bring snails within the foraging range of snail kites.

Foraging strategy may also contribute to the increased snail capture rates in off-lake wetlands. The increased prevalence of perch hunting in off-lake wetlands could reflect either increased snail densities (extensive foraging flights would not be required to locate snails), increased densities of perches (trees, snags, fence poles, etc.) directly adjacent to foraging substrates in off-lake wetlands, or a combination of increased snails and perches. Either way, this energetically cheaper foraging technique was preferred in off-lake wetlands.

Assuming that snail kites have no preference for one nesting location over another on the lake, we would expect snail kite nest density to be fairly uniform across nesting areas. However, we did not observe this in our study area in 2010 and 2011. In both years, the highest snail kite nest densities were either directly in or adjacent to Shingle Marsh, an off-lake wetland (Figure 5). Given the high densities of snail kites nesting in this area combined with the relatively high foraging rates of snail kites foraging in the off-lake wetland, it is reasonable to infer that snail kites preferred the area, at least in part, because of increased foraging success. A similar attraction of snail kites to sites recently invaded by apple snails has been observed both in Panama and Ecuador (Angehr 1999; Horgan et al. 2014).

Shingle Marsh was the only off-lake wetland adjacent to Lake Toho that we observed snail kites using as a nesting area. Unlike the other off-lake wetlands used by snail kites for foraging, Shingle Marsh contained a variety of vegetation structures used by snail kites as nesting sites, primarily willow Salix spp. and cypress trees Taxodium spp.. Shingle Marsh is only 54 ha in area and is completely surrounded by upland habitats (pasture, oak hammocks, or disturbed levees). Water levels appear to be driven mainly by precipitation events; there is no observable natural water exchange between Lake Toho and Shingle Marsh. The land is privately owned and managed, and it is equipped with feeder canals and a pumping system (water removal only) to empty water as needed for cattle grazing (Figure 6). The water in the marsh is relatively shallow, only reaching >1 m in depth in the canal systems, and almost all the water contains either emergent or floating vegetation.

Figure 6.

Detailed aerial imagery of the features of Shingle Marsh, a wetland adjacent to Lake Tohopekaliga in Florida. Shingle Marsh was found to be used heavily by snail kites Rostrhamus sociabilis plumbeus in 2010 and 2011. The levees impounding the marsh are shown as brown lines and the feeder canals used to distribute water throughout the marsh are shown in purple. The high water line is indicated in blue. The outflow pump used to empty water from the marsh is shown as a red circle. Trees used by snail kites as nesting locations (Taxodium spp. and Salix spp.) in 2010 are indicated with black arrows, and cattail Typha spp. patches containing snail kite nests in 2011 are outlined in green. Snail kite nests were located and monitored as part of a concurrent snail kite demography monitoring project run by the Florida Cooperative Fish and Wildlife Research Unit.

Figure 6.

Detailed aerial imagery of the features of Shingle Marsh, a wetland adjacent to Lake Tohopekaliga in Florida. Shingle Marsh was found to be used heavily by snail kites Rostrhamus sociabilis plumbeus in 2010 and 2011. The levees impounding the marsh are shown as brown lines and the feeder canals used to distribute water throughout the marsh are shown in purple. The high water line is indicated in blue. The outflow pump used to empty water from the marsh is shown as a red circle. Trees used by snail kites as nesting locations (Taxodium spp. and Salix spp.) in 2010 are indicated with black arrows, and cattail Typha spp. patches containing snail kite nests in 2011 are outlined in green. Snail kite nests were located and monitored as part of a concurrent snail kite demography monitoring project run by the Florida Cooperative Fish and Wildlife Research Unit.

Close modal

Given the small area, unpredictable hydroperiods, proximity of upland habitats, lack of open water, and shallow depths relative to snail kite nesting areas on the main body of Lake Toho, we expected that snail kite nests built in Shingle Marsh would be exposed to a variety of terrestrial predators such as raccoons Procyon lotor, great-horned owls Bubo virginianus, and rat snakes Pantherophis alleghaniensis. Terrestrial predators were the leading cause of snail kite nest failures in the study area in 2010 and 2011 (Olbert 2013), and we expected nests in Shingle Marsh would have lowered survival rates accordingly. However, in the one year with sufficient data to make the comparison (2010), the survival rates of snail kite nests within Shingle Marsh did not differ significantly from the survival rates of nests built on the main body of Lake Toho (Figure 4). It is worth noting that in June 2010 the landowner of Shingle Marsh began pumping water out of the area, and lowered water levels by approximately 20 cm in 6 d (personal observation), leaving two nests dry. Both of these nests were depredated by raccoons. The owner was notified of this, and ceased pumping, after which water levels stabilized. These observations do not definitively identify nests in Shingle Marsh as more prone to failure, but they do illustrate the type of hazards that snail kite nests might be exposed to in novel wetlands. This situation also illustrates that without monitoring and proper management, novel wetlands could prove dangerous to nesting snail kites.

Off-lake wetlands did appear attractive to breeding snail kites and snail kites had higher snail capture probabilities in these areas. However given our inconclusive nest-success data, we cannot say that snail kites suffered any ill effects from nesting in Shingle Marsh, and are thus unable to conclude that Shingle Marsh functioned as an ecological trap in 2010 (Schlaepfer et al. 2002; Robertson and Hutto 2006). We are unable to address this question in 2011 because, for the most part, snail kites did not build nests within the marsh. Snail kites still foraged extensively within the marsh, and did so more efficiently than on the main body of the lake. However, only two nests were built within the marsh (as compared to 17 in 2011). The most obvious cause of this difference in nest numbers is the fact that water levels in Shingle Marsh were approximately 50–30 cm shallower in 2011 than in 2010, likely because of decreased 2010 winter rainfall (personal observation), which made the area unattractive for snail kite nesting (Sykes 1987a, 1987c). The nests, instead, were placed in the next nearest suitable nesting substrate, cattail Typha spp. patches on the main body of the lake, approximately 200 m east of Shingle Marsh.

The differences in how snail kites used Shingle Marsh in 2010 (foraging and nesting area) compared to 2011 (foraging area only) highlights the need for careful monitoring and management of novel ecosystems (Lindenmayer et al. 2008; Seastedt et al. 2008). As is the case with many novel ecosystems, the effects of novel habitat use by snail kites are likely context-dependent (Pyšek et al. 2012), and could not have been fully observed if foraging behavior and nesting success were examined separately or only in one year. These effects are not likely to be consistent across all novel wetlands or even the same wetland from year to year. Our results demonstrate the importance of habitat differences in determining the role of an introduced species. The two habitats of note in this study, Lake Toho and the surrounding ephemeral wetlands, were often only separated by a few meters and both contained the same exotic species of snail. However, the snail kites used the two habitats in very different ways.

These results show evidence of a novel ecosystem (created primarily by the combination of a human-altered landscape and an introduced species) providing conservation value to an endangered species. However, our results also underscore the importance of traditional habitats. In both years, the majority of snail kites that we observed foraged exclusively in traditional on-lake foraging areas, while the number exclusively foraging in novel wetlands fluctuated greatly. Our conclusions provide evidence both of the potential value of novel ecosystems and the importance of traditional habitats.

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 authors for the article

Table S1. Description of variables contained in Table S2 and Table S3 used for the analysis of snail kite Rostrhamus sociabilis plumbeus foraging and nesting on Lake Tohopekaliga in Florida in 2010 and 2011.

Found at DOI: 10.3996/022016-JFWM-008.s1; (9 KB XLSX). Data available from the Dryad Digital Repository: http://doi.org/10.5061/dryad.mm820.

Table S2. Foraging bout data collected from breeding snail kites Rostrhamus sociabilis plumbeus on Lake Tohopekaliga in Florida in 2010 and 2011. These data were used to analyze the differences in foraging success and foraging behavior between snail kites using off-lake wetlands and those using the main body of Lake Tohopekaliga.

Found at DOI: 10.3996/022016-JFWM-008.s2; (23 KB XLSX).

Table S3. Nest check data collected at snail kite Rostrhamus sociabilis plumbeus nests on Lake Tohopekaliga in Florida in 2010 and 2011. These data were used to analyze the differences between the daily survival rates of snail kite nests occurring on off-lake wetlands and those occurring on the main body of Lake Tohopekaliga.

Found at DOI: 10.3996/022016-JFWM-008.s3 (24 KB XLSX).

Reference S1. Desa M. 2008. How aquatic fauna responded to large scale lake management in Lake Tohopekaliga, Florida. Master's thesis. Gainesville: University of Florida.

Found at DOI: 10.3996/022016-JFWM-008.s4; (2672 KB PDF).

Reference S2. Fletcher R, Robertson E, Reichert B, Cattau C, Wilcox R, Zweig C, Jeffrey B, Olbert J, Pias K, Kitchens W. 2015. Snail kite demography 5-year report. Jacksonville, Florida: Florida Cooperative Fish and Wildlife Research Unit to U.S. Army Corp of Engineers.

Found at DOI: 10.3996/022016-JFWM-008.s5; (3944 KB PDF).

Reference S3. HDR Engineering Inc. 1989. Technical report for the development of a surface water improvement and management plan for Lake Tohopekaliga/East Lake Tohopekaliga. Tampa, Florida: HDR Engineering.

Found at DOI: 10.3996/022016-JFWM-008.s6; (16026 KB PDF).

Reference S4. Olbert J. 2013. The breeding ecology of endangered snail kites Rostrhamus sociabilis plumbeus on a primary nesting site in Central Florida, USA. Master's thesis. Gainesville: University of Florida.

Found at DOI: 10.3996/022016-JFWM-008.s7 (2863 KB PDF).

Reference S5. Ramakrishnan V. 2007. Salinity, pH, temperature, desiccation, and hypoxia tolerance in the invasive freshwater apple snail Pomacea insularum. Doctoral dissertation. Arlington: University of Texas.

Found at DOI: 10.3996/022016-JFWM-008.s8 (1765 KB PDF).

Reference S6. Reichert B, Cattau C, Kitchens W, Fletcher R, Olbert J, Pias K, Zweig C. 2011. Snail kite demography annual report 2011. Jacksonville, Florida: Florida Fish and Wildlife Cooperative Research Unit to U.S. Army Corp of Engineers.

Found at DOI: 10.3996/022016-JFWM-008.s9; (1584 KB PDF).

Reference S7. Richardson JR, Bryant WL, Kitchens WM, Mattson JE, Pope KR. 1990. An evaluation of refuge habitats and relationships to water quality, quantity, and hydroperiod: a synthesis report. Gainesville, Florida: Florida Cooperative Fish and Wildlife Research Unit.

Found at DOI: 10.3996/022016-JFWM-008.s10; (3920 KB PDF).

Thank you to C. Sebright, S. Behmke, M. Ford, N. Belfry, C. Jennings, J. Wood, and E. Butler for the hard field work they put toward this project. Thank you to J. Olbert for coordination and cooperation with her study of snail kite nesting on Lake Toho. Thank you to Dr J. Morrison for her continued support and assistance. Special thanks to Dr L. Crampton for presubmission manuscript review. Thank you to the Associate Editor of the Journal of Fish and Wildlife Management and the reviewers of this manuscript for their insightful comments and critiques. Work for this study was supported by the Florida Fish and Wildlife Conservation Commission under Grant Number FWC10054, the U.S. Fish and Wildlife Service under Agreement Number 401819G578, and the U.S. Army Corp of Engineers under Contract Number W912HZ-10-2-0028.

Any use of trade, product, website, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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Author notes

Citation: Pias KE, Fletcher RJ, Kitchens WM. 2016. Assessing the value of novel habitats to snail kites through foraging behavior and nest survival. Journal of Fish and Wildlife Management 7(2):449–460; e1944-687X. doi: 10.3996/022016-JFWM-008

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.

Supplemental Material