Current Knowledge and Conservation Status of the Gray-Headed Chickadee in North America

The gray-headed chickadee Poecile cinctus is a small songbird distributed across portions of northern Europe, Asia, and North America. Three subspecies represent it in the Palearctic and one in the Nearctic and it is the only member of the family Paridae present in both regions. In the Nearctic, the endemic North American subspecies P. cinctus lathami historically inhabited boreal forests and Arctic shrublands in Alaska, the Yukon Territory, and Northwest Territories. Formerly referred to as the Siberian tit, the species was sparsely distributed in North America but ornithologists considered it locally common in some areas as recently as the 1960s (Grinnell 1900; Murie 1928; Hines 1963). The species is nonmigratory, feeds mainly on insects and seeds, and nests in cavities. The harsh northern climates that it inhabits, its small population size, and its sparse distribution make it potentially susceptible to abrupt population decline (Hanski and Gilpin 199; Hailman and Haftorn 1995). Further, researchers have not formally studied the species in the field in North America, have only ever banded two individuals, and because the species inhabits remote, difficult to access wilderness locations year round, most large-scale survey and monitoring programs have not monitored or even detected it. Collectively, these characteristics make the gray-headed chickadee one of the least understood avian species in North America.

Because of the lack of basic information on this rare species in North America, anecdotal observations suggesting it may be declining in abundance, a life history that may predispose it to declines, and lack of contemporary research, we initiated efforts to better understand the current distribution and abundance of this species. From 2010 to 2017, we conducted species-specific field surveys in northern Alaska, solicited new observations and information from other biologists and the public through a citizen science campaign, searched available museum and observational records, and compiled all resulting reliable occurrence records into one database. Based on these efforts, we present information that collectively represents the majority of what we know about the gray-headed chickadee in North America. Our specific research objectives were to 1) provide a contemporary summary of pertinent background information for the species in North America, 2) assess the likelihood that the species has recently declined in distribution or abundance in North America, and 3) recommend next steps for future research to increase our understanding of this enigmatic species.

We conducted field surveys in northern Alaska and collated information from across the species' distribution in Alaska and the Yukon and Northwest Territories. Alaska state statute 16.05.815(d) protects locations of sensitive wildlife species such as gray-headed chickadees; we therefore provide specific occurrence record locations only when they are publicly available elsewhere and relatively well known. We refer to the following generalized locations throughout:

1) The Brooks Range (Nowacki et al. 2001) is the northernmost mountain range in Alaska, spanning the state from the northern Yukon Territory westward toward the Chukchi Sea, including both south- and north-facing slopes. The south-facing slopes are interspersed with numerous creeks and rivers and habitat transitions southward from tundra to shrubs to the tree line and into boreal forest.

2) The Brooks Foothills (Nowacki et al. 2001) are the northern side of the Brooks Range and associated hills from northwest Yukon Territory to approximately Point Hope on the Chukchi Sea. This area, which consists of the mountains and low rolling hills interspersed by north-flowing rivers, provides gray-headed chickadees isolated pockets of potential tree and shrub habitat. Extensive wetlands cover the area to the north of the foothills, which does not include chickadee habitat.

3) The Alaska Range (Nowacki et al. 2001) is a large mountain range between Fairbanks and Anchorage that occurs at the southern extent of the species' historical range. It is also interspersed with numerous waterways; boreal forest surrounds the mountains to the north and vegetation is primarily tundra to the south.

4) Interior Alaska is an area roughly centered on Fairbanks, Alaska, and bounded to the north by the Brooks Range and to the south by the Alaska Range. This area includes multiple highways and the towns of Delta Junction, Tok, Fort Yukon, and others.

5) The Arctic National Wildlife Refuge, Alaska's largest refuge, is located in the northeast corner of the state that includes portions of the eastern Brooks Foothills, Brooks Range, and Interior Alaska.

Because of the general lack of information available for this species, we thought it important to present pertinent published and previously unpublished information in one cohesive summary to provide a clear, contemporary, and more comprehensive account of our state of knowledge in North America. Though Hailman and Haftorn (1995) present a useful summary, their account is outdated and doesn't include information from some unpublished sources such as personal accounts and local expertise. Further, we failed to find a location where historical and contemporary information had been gathered and summarized for this species. We therefore compiled information from all available sources and synthesized the information collectively. Though we present this summary as results, we recognize it is a combination of both new and previously published information.

We conducted focused field surveys to determine whether gray-headed chickadees were still present at previously occupied sites or nearby areas with similar habitats. We consciously chose nonrandom survey locations and methods to maximize the likelihood of finding extant populations and detecting the species if present. We surveyed five locations where gray-headed chickadees occurred historically and one location that included a substantial amount of potential nesting habitat, but where the species had not been previously documented (Table 1). Surveys consisted of walking, snowshoeing, or skiing through potential habitat in April–July (corresponding to the estimated preincubation, incubation, nestling, or fledgling period). We conducted surveys with one to three trained observers who navigated through or along potential habitat stopping every 100–400 m to listen as conditions dictated. At each stop, observers either played gray-headed chickadee vocalizations on a Foxpro NX4 Game Caller (Foxpro Inc., Lewistown, PA) for 30–60 s and then listened for 2–5 min before moving on or simply listened passively without the call playback for 2–5 min. We attempted to conduct most surveys within 4 h of sunrise when birds should be most active and winds calm but timing varied and was sometimes limited by access and weather. We did not conduct surveys in heavy rain or wind when conditions substantially compromised hearing. We also conducted passive surveys from single locations for extended periods of time (1–4 h) in what we subjectively determined was particularly promising habitat, especially if habitat was patchily distributed and surrounded by poor habitat (e.g., isolated forest patches in the Brooks Foothills). During surveys, observers also searched for potential nest cavities, recorded the latitude and longitude of each when possible, and investigated accessible cavities for potential nesting activity. We conducted surveys on 56 d during seven field efforts spanning 8 y (2010–2017), including 245 h of playback and 617 h of passive listening surveys. Combined, surveys occurred along approximately 400 linear km of potential chickadee habitat in some of the most remote parts of Alaska.

We searched for and collated occurrence records for the gray-headed chickadee in North America to create a comprehensive database of reliable historical and recent observations (N = 156 records; Table S1, Supplemental Material). Because we were interested in recent potential changes in distribution, we subjectively divided the occurrence records before and after the year 2000, mapped each group of records using Google Earth, and visually compared the resulting maps to assess potential recent changes in distribution. We were unable to determine location accuracy of many of the records, but it was likely very poor and often > 1 km. We populated this database using records from the following sources:

1) Outreach to other biologists and local experts (n = 60 records). We presented preliminary field survey results and requested information from biologists and naturalists across Alaska and western Canada at annual Boreal Partners in Flight meetings and semiannual Alaska Bird Conferences since 2011, as well as through phone calls and emails to area biologists and local experts.

2) Online museum database searches (n = 58 records). We thoroughly searched aggregator websites such as VertNet (2020) and individual online museum catalogs for specimen records of gray-headed chickadees.

3) eBird (n = 15 records). We searched online eBird (2017) records and assessed each record individually for its reliability and inclusion in the database based on the details of each report and the experience level of the reporter. If there was doubt about the reliability of the record, we did not include it in the database.

4) Published literature and unpublished agency reports (n = 17 records).

5) Citizen science outreach program (n = 4 records). Between 2010 and 2018, the Alaska Department of Fish and Game (ADF&G) conducted an outreach program requesting reports of gray-headed chickadee sightings from primarily Interior and western Alaskan communities. We distributed posters summarizing and publicizing this effort at ADF&G offices, at other agency offices, in local villages, and to interested birders. Through these efforts we received 30 reported sightings from the public, though TLB subsequently determined most to be other chickadee species based on photographs or phone discussions with citizen scientists. We considered four of the 30 reported sightings as likely gray-headed chickadees based on the detailed accounts of the observations and experience level of the observer, though none included photographs to confirm identification.

6) U.S. Geological Survey Bird Banding Lab (n = 2 records).

Taxonomists group the gray-headed chickadee in the same clade as the boreal chickadee Poecile hudsonicus and chestnut-backed chickadee Poecile rufescens (Johansson et al. 2013). There are four recognized subspecies of gray-headed chickadee (following Dickinson and Christidis 2014; Gill and Donsker 2018). Three occur in Eurasia (P. c. lapponicus, Fennoscandia east to north-central Russia; P. c. cinctus, central Russia east to the Russian Far East; and P. c. sayanus, the Altai and Sayan mountains to northwest Mongolia) and the fourth subspecies, P. c. lathami, is endemic to Alaska and northwestern Canada. Although juvenile gray-headed chickadees may be nomadic during the nonbreeding season, adults are sedentary (Virkkala 1990; Cramp and Perrins 1993). One would therefore expect that Palearctic and Nearctic populations have remained genetically isolated from each other since the beginning of the most recent postglacial period (DeCicco et al. 2017). Morphological variation among Palearctic subspecies appears to be slight and largely clinal (Dement'ev and Gladkov 1970). However, DeCicco et al. (2017) found that P. c. lathami differed from its nearest Palearctic subspecies, P. c. cinctus, in seven of 14 morphological variables, with P. c. lathami having generally darker plumage and a larger bill. Their results support the current distinction between Palearctic and Nearctic subspecies, but the authors suggest that, to better clarify its taxonomy, further research needs to include phylogenetic assessment of the species.

Researchers have well described the species' habitat associations across its Eurasian range but few have studied these associations in detail in North America (Hailman and Haftorn 1995). In general, gray-headed chickadees in North America primarily occur within mixed coniferous and deciduous forests near the northern (and in Alaska, western) edge of the tree line (Hailman and Haftorn 1995). In eastern Alaska and the Yukon Territory, the species uses spruce (Picea spp.) and willow (Salix spp.)–dominated habitats adjacent to rivers that are otherwise surrounded by open tundra (Murie 1928; Spindler et al. 1980). Hines (1963) reported that in northwest Alaska they inhabit extensive shrublands of low willow and spruce < 6 m tall. In the Brooks Foothills, the species uses isolated balsam poplar Populus balsamifera groves, at least during the spring and summer seasons (Martin 1976). Gray-headed chickadees are obligate cavity nesters and though they can modify openings, they do not generally create their own cavities. Hence, researchers think breeding habitat is restricted to sites with trees or shrubs of sufficient diameter to support existing cavities. In Europe, the species uses natural or previously excavated cavities in pine, spruce, birch (Betula spp.), and aspen (Populus spp.) for nest sites (Saari et al. 1994). In the Nearctic, the species uses cavities in spruce (Bente 1946), poplar (Tobish 1997b) and likely birch or willow, though detailed nest descriptions in North America are rare. Gray-headed chickadees did use a cliff swallow Petrochelidon pyrrhonota nest cavity along a river in the Brooks Foothills for at least seven consecutive years (A. Lang, Wilderness Birding Adventures, personal communication), indicating there is some level of plasticity in nest site selection. We do not know the extent of competition for nest sites among other cavity-nesting birds.

There is insufficient information to identify threats to gray-headed chickadees in North America with confidence. Most likely threats are those identified or proposed for Eurasian populations, including a combination of direct and indirect effects of climate change (Dale and Andreassen 2016). Increasing winter temperatures and precipitation may reduce the nutritional value and availability of stored food (e.g., Sechley et al. 2015), which could directly influence chickadee survival or breeding success. Other potential effects include increased competition for nest sites and food with other chickadee species expanding northward. Dale and Andreassen (2016) found increased abundance of great tits Poecile major and willow tits Poecile montanus coincided with decreases in gray-headed chickadees in southern Norway. A similar pattern between boreal chickadees and gray-headed chickadees has been observed in parts of Alaska (see Discussion), though cogeners do not occur in the Brooks Foothills, making competition there unlikely. Additionally, we speculate gray-headed chickadees could be hybridizing with boreal chickadees (wherever cogeners occur), causing either demographic or genetic swamping and subsequent population decline (Todesco et al. 2016). Gray-headed chickadees have hybridized with willow tits in Europe (Järvinen et al. 1985). Lait et al. (2012) documented the more distantly related black-capped chickadee Poecile atricapillus hybridizing with boreal chickadees, suggesting that hybridization between the more closely related gray-headed and boreal chickadees is possible. Although highly speculative and lacking any observations of bill deformities, the species could be impacted by a recently documented avian keratin disorder (Zylberberg et al. 2018) that Handel at al. (2010) observed in other bird species (especially chickadees) in Alaska in recent decades.

Several national and regional assessments include gray-headed chickadees in conservation designations though inclusion is inconsistent and subsequently confusing. Audubon Alaska includes the species in the Red List of declining bird populations in their 2017 Alaska WatchList (Warnock 2017) citing its small population size, rarity, anecdotal reports of decline, and lack of study. Audubon (2020) contrarily states “Scarce and local in North America, but probably faces no serious threats in its remote haunts.” NatureServe lists the species as secure (G5) globally, but vulnerable (S3) in Alaska, imperiled (S2) in the Northwest Territories, and critically imperiled (S1) in the Yukon Territory but provides no rationale for these rankings (NatureServe 2018). Sinclair et al. (2003) classifies the species a rare resident in the Yukon Territory. The Alaska State Wildlife Action Plan considers the gray-headed chickadee a high-priority species of greatest conservation need (ADF&G 2015). However, the species is not included as a species of concern in the continental Landbird Conservation Plan (Rosenberg et. al 2016) and has no designation under Canada's Species at Risk Act (SARA 2002, as amended) or the U.S. Endangered Species Act (ESA 1973, as amended). To our knowledge, no states or provinces list the species as threatened or endangered.

We detected gray-headed chickadees on two occasions during 862 h of field surveys spanning 8 y (Table 1). We detected and photographed a single individual during a playback survey in April 2011 in the Arctic National Wildlife Refuge. It occurred in a narrow stand of mature spruce along a small creek surrounded by open tundra within the headwaters of the Old Crow River. The bird responded almost immediately following a call playback session by vocalizing from the top of a tall spruce tree. While the call was still playing, it flew to within 10 m of the observers and flitted among them in dense willow shrubs. It responded regularly to the recording by vocalizing and appearing to investigate the source of the call, allowing it to be photographed at close range. Once the recording stopped, the bird drifted off quickly through the willows. Upon playing the recording a second time, the individual quickly returned, again vocalizing and appearing to investigate the call. We stopped playing the call in hopes of returning and capturing the individual at a later time. It again quickly drifted off through the willows and into a mature spruce stand. Though we returned to that location repeatedly in subsequent days and spent multiple hours there playing calls, we did not detect it again. The second detection of the species during field surveys occurred in a balsam poplar grove during a passive survey in April 2013 along the Canning River, also in the Arctic National Wildlife Refuge. We observed two individuals flying through a poplar grove, perching briefly between flights. We were unable to photograph the birds but confirmed their identity via observation through binoculars and audibly by their calls. The detection lasted approximately 30 s and we were unable to relocate either bird during subsequent visits to that site in the following days. We also failed to detect the species at that location during a follow-up trip in July 2013 when we conducted call playback surveys and passive mist-netting in hope of capturing the species. We did not detect evidence of nesting at any survey location.

We found 108 occurrence records in North America from 1864–1999 (Figure 1A). Records were present in every decade since 1864 except for the 1930s–1950s. Based on these records, the species historically occurred broadly across Alaska from the Yukon–Kuskokwim Delta to the northern foothills of the Brooks Range in Alaska (∼ 61–69°N). In Canada, the species primarily occurred in northern regions of the Yukon Territory and Northwest Territories (65–69°N) from Cape Bathurst west to the United States–Canada border. Observers described gray-headed chickadees as locally common in the Noatak and Kobuk river drainages, Alaska, through the first half of the 1900s (McLenegan 1889; Grinnell 1900; Hines 1963) and in the Old Crow Flats, Yukon Territory, Canada, in the 1920s (Murie 1928). Historical sightings in Interior Alaska around Fairbanks occurred primarily during fall and winter (Gibson 2011), suggesting patterns of juvenile dispersal and nomadism that are similarly exhibited by Palearctic populations (Järvinen and Hilden 1981).

We found 48 occurrence records in Alaska since 2000, 32 of which were repeated annual detections from the same two locations in the Arctic National Wildlife Refuge (Figure 1B). We found only one reliable record outside the vicinity of the Brooks Range. We found no recent reliable records of the species from Interior Alaska near Fairbanks, where there are more roads, people, bird surveys (e.g., Breeding Bird Survey and Christmas Bird Count) and hence, more opportunities to observe this species than in any other part of its historical distribution. We found an absence of records in southwest Alaska between Bethel and Grayling though a cluster of observations did exist from 1984 to 2001 along the Yukon River near Galena. There have been no reported sightings there since even though the biologist responsible for most of those sightings has continued to search for the species in this area (K. Bodony, U.S. Fish and Wildlife Service, personal communication).

In Canada, we found only two reliable occurrence records since 2000. One is from a June 2014 record of a single individual observed by a biologist near Old Crow, Yukon Territory, relatively close to the location where O. Murie reported them as common and collected a dozen specimens in 1926 (Murie 1928). The other record is from July 2008 along the Firth River in Ivvavik National Park. Records show a cluster of historical observations in Northwest Territories near Reindeer Station in 1989 and 1990, but we found no detections of this species since that time, including during recent Bird Survey Checklist surveys and Breeding Bird Surveys (C. Eckert, Yukon Government Department of Environment, personal communication).

Presently, the species is still regularly, though rarely (1–3 sightings per year), reported in only two small areas in the Brooks Range. The first is in northwestern Alaska within the Noatak National Preserve near the confluence of the Kelly and Noatak rivers (Figure 1B, site 1). Birders attempting to observe the species know this area well and regularly visit and informally survey it. There was a cluster of observations there in 2016, though we know of no reliable sightings in that area since. The second area is along the northward-flowing rivers of the Arctic National Wildlife Refuge (Figure 1B). This location has the best documented recent occurrence records including sightings from agency biologists, the birding tour company mentioned above, and recreational birders including photographic documentation.

The species' global population estimate is 2,000,000 individuals (Partners in Flight 2013), though we cannot determine accuracy of this estimate. Gray-headed chickadee abundance decreased by 90% between the 1940s and 1970s in Finland (Väisänen et al. 1986) and by a similar amount in Norway between 1980 and 2011 (Dale and Andreassen 2016). Dale and Andreassen (2016) suggest climate change, interspecific competition, and forestry practices as potential causes of the decline in Norway. Little additional information is available on size and status of the species outside of Fennoscandia. No accurate population size estimate exists for North America (Hailman and Haftorn 1995) and Partners in Flight's estimate of fewer than 5,000 individuals based on expert knowledge is speculative at best (Rosenberg et al. 2016). Neither the North American Breeding Bird Survey (Pardieck et al. 2018) nor the off-road Alaska Landbird Monitoring Survey that is similar to the Breeding Bird Survey but occurs in more remote parts of Alaska (C. Handel, United States Geological Survey, personal communication) have detected gray-headed chickadees. Other extensive general avian surveys in the Brooks Range in the 2000s (Tibbitts et al. 2006; DeGroot and McMillan 2012) also failed to detect the species. Two reports of gray-headed chickadees exist from Christmas Bird Counts in Alaska (in 1975 and 1984, National Audubon Society 2018) but we cannot determine accuracy of these reports and the sample size is too small for estimating population size.

Based upon a thorough review of the best available information, targeted surveys in historical locations, multidecadal observations at two locations, and discussions with management agency staff across the species' distribution, we find it hard to believe a species that is highly sought after (and subsequently reported) by birders but for which only a handful are reliably reported annually could be present on the landscape in numbers greater than a few thousand. Further, in places where biologists previously considered the species common, ADF&G and others have failed to detect them at all, again suggesting the current population is very small.

Two locations where observers using consistent methods have regularly reported gray-headed chickadees in recent decades may be useful to infer potential change in abundance.

1) Brooks Foothills. Since 1997, a birding guide company has annually observed a very small, isolated population of nesting gray-headed chickadees along a river in the northern portion of the Arctic National Wildlife Refuge. The group has searched the same breeding habitat and nest cavities along the same river over the past 22 y and typically found 1–2 nests each year. However, they have detected no nests and only one nonbreeding adult since 2015 (B. Dittrick and A. Lang, Wilderness Birding Adventures, personal communication). Additionally, in 2018, the birding guides deployed automated recording units at three locations along the river where they had previously regularly detected the species. The automated recording units recorded bird calls continuously for 2 wk in late June and early July during the nestling and fledgling period. Neither the recordings nor human observers detected chickadees of any species.

2) Porcupine River drainage, Alaska. In the eastern portion of the Arctic National Wildlife Refuge, H. Korth commonly observed gray-headed chickadees throughout each winter feeding on animal carcasses near trapper cabins that he and his family have used annually since 1989. Gray-headed chickadees were the most common chickadee present, followed in descending order by boreal and black-capped chickadees. Gray-headed chickadees abruptly became rare in this area around 2011 and Korth has not detected the species since 2013. Boreal chickadees are now the most common chickadee species observed and it appears gray-headed chickadees are absent (H. Korth, no affiliation, personal communication).

We conclude the gray-headed chickadee in North America has likely recently declined in abundance and distribution. We base this conclusion on multiple lines of evidence. First, although we have conducted 862 h of gray-headed chickadee surveys at historical sites with presumably some of the best available habitat, we detected only three individuals and observed no signs of breeding. Second, it appears the species' distribution has likely contracted and that it no longer regularly occurs in southwestern or Interior Alaska, or the Northwest Territories. Third, at the two locations in Alaska for which there are reliable, long-term occupancy records in recent history, the species has become absent at both sites in the past 5–10 y. Recent records of nesting gray-headed chickadees are rare and observers report only a few reliable sightings of gray-headed chickadees annually in Alaska and Canada, nearly all of them from within Alaska's Brooks Range. Hence, though we acknowledge that we base our conclusion on limited information and that one of the locations with long-term data had only a few nests that were observed annually, all the available information is consistent with a recent decline in abundance and distribution.

We acknowledge this species may occur in yet-to-be-discovered locations, or given its visual similarity to other chickadees, may be present and observed by members of the public that are not aware of its uniqueness and hence, do not mention their occurrence to others. Evaluating the reliability of observational reports is an imperfect process and we admit this adds additional uncertainty to the database we amassed and the conclusions we drew from those data. We also recognize that the early 1900s encompassed increased activity by museum collectors. A potential explanation for the paucity of recent records outside of the Brooks Range could be lower contemporary search effort compared to the height of collecting in the early 1900s. However, the remote habitats of gray-headed chickadees are undoubtedly more accessible than ever via modern aircraft and off-road vehicles. Additionally, modern birders are highly motivated to observe this species and recreational trips dedicated to finding this species occur regularly in Alaska. Last, recent surveys and field efforts, as well as more commonly used and readily available reporting outlets (e.g., eBird), suggest that the lack of recent observations is more likely a result of changes in abundance or distribution rather than decreased search effort. If anything, the lack of recent observations despite the likely increased search and reporting efforts lends more support to our conclusion of declining abundance and distribution.

Because we used primarily single-visit surveys, we could not confirm the absence of gray-headed chickadees from field survey locations. However, the fact that we failed to detect the species where it previously occurred, and when we did detect it, we observed only one or two individuals very briefly with no indication of breeding, is particularly useful when placed into the context of historical records. For example, Martin (1976) described the species as “probably locally common” during a multiweek field program along the Kongakut River in the Brooks Range of the Arctic National Wildlife Refuge in 1976. Over the course of a week, his party observed multiple pairs and individuals in poplar stands within a couple specific drainages. We conducted 96 h of focused surveys in June 2017 over the course of 9 d at the same locations where Martin (1976) considered them likely common and detected no chickadees or signs of nesting. Similarly, Hines observed and collected gray-headed chickadees from the confluence of the Kelly and Noatak rivers during 6 and 10 d in June–September of 1960 and 1961, respectively (Hines 1963). Hines considered gray-headed chickadees to be widely distributed and more common in the area than boreal chickadees, the latter being observed on several occasions in small flocks of gray-headed chickadees in 1960 and on only two occasions during 1961 (Hines 1963). We conducted gray-headed chickadee surveys in the same area during an 8-d visit in April 2012. We detected 62 boreal chickadees and no gray-headed chickadees during 50 h of playback and 114 h of passive listening surveys that covered 70 linear km of habitat. Though this was only one sampling effort that included half as many days of observations as Hines (1963), our survey results were strikingly different and suggestive of changes in local abundance for both species.

We recognize that we have based our conclusions and speculations on very limited information when compared to many other North American wildlife species. Most of the occurrence records we collected did not quantify or describe search effort or methods, making direct or fine-scale comparisons among them difficult if not inappropriate. When sources did provide this information (e.g., Hines 1963, Martin 1976), a closer comparison of their observations and search effort with ours lends additional support to our conclusions. We also note that these types of data are presence-only; inferring absence because of a lack of records in an area is problematic and must be done cautiously. Throughout this study, we attempted to carefully interpret results and focus on patterns arising from multiple lines of evidence. To the best of our abilities, we have accumulated most of the known, reliable information about this species in North America and, as such, this represents the best available information to date. If our assessment is accurate, then the gray-headed chickadee may be one of North America's least populous and most imperiled bird species. There is an urgent need to identify where the species still occurs and to determine key aspects of its life history and status, including factors limiting population size. It is our hope that this paper highlights the dearth of information on this rare species and spurs others into action to increase our understanding of this unique and enigmatic songbird of the north.

To better determine the species' conservation status, a more accurate assessment of its population size and trend is imperative. The highest priority first step toward this goal is locating extant populations. Standardized, repeated surveys that rigorously assess occupancy as well as absence should target locations with the highest probability of breeding pairs; in other words, sites where observers have recently detected the species. The Noatak River and its major tributaries in northwestern Alaska, isolated poplar groves in the Brooks Foothills, and the central Brooks Range between the two locations where the observers still rarely spot the species are likely the most suitable places to begin. The Old Crow Flats area in the Yukon Territory is also deserving of additional focused survey effort. If surveys do find extant populations, survey methods should be refined and detection probability of various methods rigorously assessed. Researchers should obtain more precise location data and use it to create habitat models to predict where the species most likely still occurs. Additional surveys can then use these models to guide siting efforts. Because of the size and remoteness of the gray-headed chickadee's historical distribution, it would also be beneficial to solicit the birding community for new, verifiable records to inform habitat models and surveys. If or as observers discover populations, researchers can then begin the process of documenting life history information including habitat associations, demographic rates, and interactions among congeners. Studies that investigate gene flow between gray-headed chickadees and boreal chickadees would be informative as would comparative studies that include the more populous, yet declining Palearctic populations.

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. Summary of gray-headed chickadee Poecile cinctus lathami occurrence data in North America collected from available sources from 1864 onward. We have withheld sensitive wildlife location and personal data in accordance with Alaska State Statute 16.05.815(d).

Found at DOI: https://doi.org/10.3996/082019-JFWM-072.S1 (20 KB XLSX); https://doi.org/10.3996/082019-JFWM-072.S2 (13 KB DOCX).

Reference S1.[ADF&G] Alaska Department of Fish and Game. 2015. Alaska wildlife action plan. Juneau, Alaska: ADF&G.

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Reference S2.DeGroot, KA, McMillan J. 2012. Landbird monitoring in the Arctic Network: Gates of the Arctic National Park and Preserve and Noatak National Preserve (2010 report). Natural Resource Data Series NPS/ARCN/NRDS-2012/315. Fort Collins, Colorado: National Park Service.

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Reference S3.Gibson, DD. 2011. Nesting shorebirds and landbirds of interior Alaska: boreal zone breeding species in the avian families Charadriidae, Scolopacidae, Strigidae, Alcedinidae, Picidae, Tyrannidae, Laniidae, Corvidae, Alaudidae, Hirundinidae, Paridae, Sittidae, Certhiidae, Cinclidae, Regulidae, Phylloscopidae, Turdidae, Sturnidae, Motacillidae, Bombycillidae, Calcariidae, Parulidae, Emberizidae, Icteridae, and Fringillidae. Fairbanks, Alaska: U.S. Geological Survey report, contract no. G10PX02562.

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Reference S6.Spindler MA, Mouton MA, MacDonald SO. 1980. Biological surveys in the Firth–Mancha Research Natural Area, Alaska, 1979–1980. Fairbanks, Alaska: U.S. Fish and Wildlife Service Arctic National Wildlife Refuge.

Found at DOI: https://doi.org/10.3996/082019-JFWM-072.S8 (4.88 MB PDF); also available at https://catalog.data.gov/dataset/biological-surveys-in-the-firth-mancha-research-natural-area-alaska-1979-1980.

Reference S7.Tibbitts TL, Ruthrauff DR, Gill RE Jr, Handel CM. 2006. Inventory of montane-nesting birds in the Arctic network of National Parks, Alaska. Fairbanks, Alaska: Arctic Network Inventory and Monitoring Program, USDI National Park Service. NPS/AKARCN/NRTR-2006/02.

Found at DOI: https://doi.org/10.3996/082019-JFWM-072.S9 (20.11 MB PDF); also available at https://www.nps.gov/gaar/learn/nature/upload/NPS_AKRARCN_NRTR-2005-01-2.pdf.

We thank Trevor Haines, Steve Kendall, Tory Rhodes, and Jeff Wells for assisting with field work under challenging conditions. We also thank Heimo Korth, Bob Dittrick, Aaron Lang, and Wilderness Birding Adventures for sharing invaluable long-term observations and rare insights about this species. Lisa Mahon, Tracey Gotthardt, Steve Matsuoka, and David Haukos reviewed and greatly improved previous drafts of this manuscript. Funding for this work was provided by the Alaska Department of Fish and Game through the federal State Wildlife Grant Program. The U.S. Fish and Wildlife Service and the National Park Service provided in-kind field logistics support for two of the field efforts.

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