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/lp/de-gruyter/using-geolocator-data-to-address-changes-in-migration-patterns-for-gYMo3gwpbf
- Publisher
- de Gruyter
- Copyright
- © 2022 Audrey Taylor et al., published by De Gruyter
- ISSN
- 2084-8838
- eISSN
- 2084-8838
- DOI
- 10.1515/ami-2022-0118
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- See Article on Publisher Site
Abstract
Anim. Migr. 2022; 9: 1–26 Research Article Audrey Taylor*, Mary Anne Bishop, Anne Schaefer, Ron Porter, Kristine Sowl Using Geolocator Data to Address Changes in Migration Patterns for Black Turnstone https://doi.org/10.1515/ami-2022-0118 whether migration routes for this species have changed received December 17, 2021; accepted March 29, 2022 over the last 30 years. Keywords: Short-distance migrant, Rocky coast shorebird, Abstract: Black Turnstone is an obligate Pacific coast Alaska, Pacific Northwest, Warming winters shorebird that is included as a “Species of High Concern” in both the U.S. and Alaska Shorebird Conservation Plans. Specific migration routes for this species are not well understood, which makes its recent disappearance at a 1 Introduction major spring stopover site, northern Montague Island in Prince William Sound, Alaska, difficult to interpret. We Conservation efforts for non-game species like migratory tracked 23 Black Turnstones between breeding and winter- shorebirds are often prioritized based on population size, ing areas and examined migration timing, duration, and trend, range, and existing threats across a species’ annual routes used. We identified two high-use regions during cycle [1]. Such prioritization schemes for many shore- migration: 1) Cook Inlet/Shelikof Strait, Alaska, and 2) the birds that nest in the Arctic or sub-Arctic are hampered Haida Gwaii Archipelago in British Columbia/Alexander by a lack of information from the breeding grounds due Archipelago in southeastern Alaska. This second region to their remoteness, as much of the Arctic and sub-Arctic was also an important wintering area. We found that are roadless and difficult to access in the summer. This northbound migration was longer than southbound (the places additional importance on data gathered from the reverse of what is often observed in shorebirds) and that nonbreeding range and requires an understanding of staging behavior was primarily seen during northbound migratory routes, timing, and connectivity to interpret the migration. No birds were tracked to northern Montague significance of occupancy or abundance trends at impor- Island, and only a few individuals stopped anywhere in tant stopover or wintering sites. Prince William Sound. Alterations in patterns of spring Black Turnstone (Arenaria melanocephala) is a medi- herring spawn in Prince William Sound may be affecting um-sized shorebird associated exclusively with Pacific the routes and stopovers used by Black Turnstones, and coast shorelines. Both the U.S. and Alaska Shorebird Con- birds may be wintering farther north in recent decades due servation Plans list Black Turnstone as a “Species of High to warmer winter conditions. Additionally, the increasing Concern” due to a relatively small population size and sig- availability and popularity of citizen science efforts like nificant threats at breeding and non-breeding areas [1, 2] eBird has created a mechanism for disseminating obser- and it also appears on the US Fish and Wildlife Service’s vations from less accessible parts of the Black Turnstone recently released “Birds of Conservation Concern 2021” range, a fact which may confound our understanding of list [3]. An estimated 85% of the global Black Turnstone population nests on the central Yukon-Kuskokwim Delta in Alaska in low-lying salt grass meadows and sparsely vegetated habitats within 2 km of the coast [4]. During *Corresponding author: Audrey R. Taylor, Department of Biological migration and winter, the species is primarily found Sciences, University of Alaska Anchorage, 3211 Providence Drive, in rocky intertidal habitats and coastal beaches from Anchorage, Alaska 99508 USA Email: artaylor@alaska.edu Kodiak, Alaska, to Mexico [5]. Because Black Turnstone is Mary Anne Bishop, Anne Schaefer, Prince William Sound Science dependent on coastal habitats throughout the year, this Center, 1000 Orca Road, Cordova Alaska, 99574 USA species is vulnerable to habitat loss or degradation result- Ron Porter, 800 Quinard Court, Ambler, Pennsylvania 19002 USA ing from coastal pollution, infrastructure development, Kristine Sowl, Inventory and Monitoring Branch, National Wildlife Refuge System Alaska, 95 Sterling Highway, Suite 1, Homer, Alaska and climate change effects (such as more frequent and 99603 USA Open Access. © 2021 Taylor et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. 2 Taylor et al. intense coastal storms) across its range [1]. On the breed- a shift in choice of migration routes or stopover sites. To ing grounds, sea-level rise and more frequent and intense address this data gap, we studied Black Turnstone migra- storms are resulting in seasonal flooding, saltwater intru- tion in Alaska and Washington State from 2011 to 2015 sion, and changes in erosion and sedimentation rates in using light-level geolocators, which allowed us to estimate the low elevation habitats preferred for nesting [6, 7, 8]. geographic locations from patterns of ambient light and Black Turnstone has been the subject of few breed- therefore infer approximate daily positions and seasonal ing season studies because the population is relatively movement patterns of individual birds [17]. During pro- small (~100,000 birds) [4, 9] and sparsely distributed in cessing of geolocator data, latitude is derived from day remote, roadless western Alaska. The species is also dif- length and longitude from the time of solar noon, while ficult to study during the winter, when individuals aggre- error in these calculations is derived from ambiguity and gate in small, widely dispersed groups on rocky coastlines variability in the light data caused by weather, habitat, or coastal structures (e.g., docks, jetties), unlike many and bird behavior [17]. We chose to use geolocators shorebird species which congregate in large numbers on because the satellite tag technology available at the outset coastal mudflats where they can be enumerated, cap- of this study was too heavy for use on Black Turnstones. tured, banded, and resighted en masse. In particular, little We used the information provided by the geolocator data is known regarding individual Black Turnstone migration to enhance our understanding of Black Turnstone migra- routes and connectivity, and only a few major stopover sites tory routes, timing, and connectivity, and to answer the have been identified on their migration route to and from question: If geolocator-tagged Black Turnstones are not western Alaska. These include northern Montague Island stopping at Montague Island, are they using other stopo- in Alaska’s Prince William Sound (PWS) [10, 11], which ver sites in PWS, and if so, what proportion of individuals was designated an Important Bird Area for the species in use these sites? This information can be used to update 2006 by the National Audubon Society and BirdLife Inter- and improve future conservation planning efforts for this national. Surveys conducted at Montague Island during iconic Alaskan shorebird. spring 2010 showed that numbers of turnstones stopping over on northbound migration had declined substantially in the 13 years since previous surveys were conducted, 2 Methods from a single-day high of 11,300 individuals in 1997 to <4000 over 19 survey days of the same area [12]. Given that observations and gut contents from turnstones at Mon- 2.1 Study Sites tague Island indicated Black Turnstone relies heavily on herring spawn to fuel migration north from PWS in the Our primary study site for geolocator deployment was near spring [10, 11] this reduction in the number of individu- the mouth of the Tutakoke River on the Yukon-Kuskokwim als using northern Montague Island could be a result of Delta, western Alaska (61.25°N, 165.62°W), located in the a shift in migration distribution in response to the Pacific center of the main breeding range for Black Turnstones herring (Clupea pallasii) population in PWS declining in [4]. We also deployed geolocators at a breeding site at the years since the Exxon Valdez Oil Spill [13, 14]. Alterna- Cape Krusenstern, northwest Alaska (67.12°N, 163.46°W), tively, Black Turnstones may be another Alaskan species and at Oak Harbor in Puget Sound, Washington, (48.28°N, that is shifting its wintering distribution northward due 122.64°W), a wintering and stopover site (Fig. 1). to climate change, similar to Pacific flyway Black Brant The Tutakoke site is located on a flat plain of coastal (Branta bernicla nigricans) [15] and Emperor Geese (Anser tundra bisected by the Tutakoke River, which flows into canagicus) [16], and therefore changing its use of histori- the Bering Sea at the western edge of the study area. cal stopover sites. Black Turnstone habitat generally occurs in bands par- Given the already small population size of this species allel to the coast, with densities declining along a gradi- and the changes observed in numbers of individuals using ent of increasing elevation and decreasing moisture and their primary spring stopover area in PWS, there is a need salinity [4]. Along the more tidally influenced northern to reassess the conservation status of Black Turnstone. and western edge of the study area closest to the Bering However, we lack important information on migration Sea, sedge meadows form “fingers” of habitat on eroding routes of individuals through time and space, which pre- barren mudflats along the coast and the river delta. These cludes an understanding of whether observed changes in protrusions of vegetated land surrounded by mudflats the species’ use of their primary spring stopover site indi- are favored by nesting turnstones. Other individuals nest cate a decline in the breeding population size, or merely in lower densities along the edge of rivers and slightly Using Geolocator Data to Address Changes in Migration Patterns for Black Turnstone 3 inland from the coast in higher meadows, dominated by 2.2 Field Methods graminoid and dwarf shrub vegetation and dotted by thaw lakes [5]. We deployed a total of 55 geolocators on Black Turnstones The Cape Krusenstern site is located on the edge over two field seasons. We used bownet traps to capture of Cape Krusenstern Lagoon, a shallow 48 km coastal breeding turnstones on nests at Tutakoke and Cape barrier lagoon adjacent to the Chukchi Sea. The study area Krusenstern, and a combination of noose mats and a com- includes a suite of diverse wetland habitats interspersed pressed air-powered net launcher (Super Talon model, with small lagoons and hundreds of brackish lakes [18, Net-Gun, Inc.) to capture roosting birds at Oak Harbor. We 19]. Turnstone habitat in this region lacks the distinct deployed model MK12-S geolocators in 2011 and MK5780 zonation patterns of the central Yukon-Kuskokwim Delta geolocators in 2013; both models weighed approximately [5]; individuals nest in coastal graminoid meadows on 1.5g and were manufactured by Lotek Wireless/Biotrack the mainland or on small islands formed by thaw lakes Ltd, Wareham, UK. Geolocators were attached using a leg- around the main lagoon. loop harness [20] made of stretchy, flexible beading cord The Oak Harbor site is a man-made marina on the (StretchMagic™, Pepperell Braiding Company, MA). We northeast side of Whidbey Island in northern Puget also color-banded each individual, performed standard Sound. Turnstones use this site primarily as a high-tide biometric measurements, and collected whole blood on roost during the non-breeding season (August to April). filter paper for sexing. Black Turnstones cannot be sexed A small wintering population of 200-300 birds swells to in the hand [5], therefore the blood was sent to an outside approximately 1000 birds during spring migration in laboratory for genetic analysis to determine sex (Antech March and April (A. Taylor, pers. obs.). Birds roost on con- Diagnostics, Fountain Valley, CA). crete docks, boat decks, and log pilings while waiting for We revisited our field sites multiple times during the ebbing tide to expose foraging areas dispersed around 2012 (Oak Harbor) and 2014 and 2015 (Tutakoke and Cape the Oak Harbor/Penn Cove vicinity. Krusenstern) to recover geolocators from returning birds. Recapture of birds with geolocators was accomplished using the same methods as described for initial capture. All capture procedures and protocols were approved by one or more Institutional Animal Care and Use Commit- tees (Prince William Sound Science Center (2011-2013); University of Alaska Anchorage Protocol Nos. 461500 and 463550 (2013-2015). 2.3 Geolocator Analysis Recovered geolocators were downloaded and the data initially processed using the BASTrak software suite pro- vided by the British Antarctic Survey [21]. The locations were determined primarily by longitude averaging and intersection with the coastline. In places of north/south coastal orientation, the latitude cluster was examined to find the least shaded fixes using methods reported in [22]. We calibrated the geolocator output using post-deploy- ment fixes collected prior to the individual’s departure from the capture site (Yukon Delta’s Tutakoke breeding grounds, Cape Krusenstern breeding grounds, or Oak Harbor wintering area). We used a fixed light threshold value (16) and a minimum night length of one hour to Figure 1. Location of geolocator deployment sites where breeding delineate day to night transitions and to filter out false (Tutakoke and Cape Krusenstern) and wintering (Oak Harbor) Black locations caused by shading. We ignored fixes collected Turnstones were captured in 2011-2013. Also shown is Montague within ± 15 days of the fall and spring equinoxes when lat- Island, a historic northbound stopover site. itude cannot be reliably estimated [17]. 4 Taylor et al. We mapped the output from each geolocator in Google Flock sizes were estimated and GPS coordinates recorded Earth after analysis with BASTrak software and eliminated for each observation. obvious longitudinal outliers. For Black Turnstones, these outliers were mostly fixes indicating the birds were occu- pying inland, terrestrial sites or sites in eastern or central 3 Results Canada, opposite the expected direction of migration. To determine stopover sites during northbound and south- We recovered 18 geolocators from Black Turnstones that bound migration, we evaluated each track one fix at had been outfitted with geolocators during 2013 at the a time to identify periods when a bird was traveling vs. Tutakoke site, and two geolocators from birds tagged in stationary. We used the recorded maximum light levels to 2013 at the Cape Krusenstern site, all upon their return to determine up to two locations per day. We then defined a breeding territories in 2014. One of the Tutakoke units did stopover site as a location for which three or more consec- not record any usable data so was excluded from further utive fixes were recorded (total length 36+ hours) and a analysis. We recovered an additional geolocator during a staging area as a location where a bird was recorded for > short trip to the Tutakoke site in 2015; this unit provided seven days. We plotted direct connections between stopo- two full years of migration and wintering data for a single ver sites, but actual travel routes may have deviated from individual. In 2012 at Oak Harbor, we recovered three geo- direct-line paths. locators from individuals tagged in spring 2011. In total, Because geolocators are sensitive to the effects of our data represent migration patterns of 15 males and shading due to factors including weather conditions, 8 females (n=23; see Table 1 for breakdown by site and BASTrak output displayed substantial noise at each stop- sex). Geolocators recovered from the Cape Krusenstern over location, resulting in a cluster of fixes. We assessed and Oak Harbor birds and all but four of the Tutakoke weather conditions during each flight and at each stop- birds provided a full year of data, including northbound over location using archived weather and atmospheric and southbound migration dates and durations, as well pressure data from the National Oceanic and Atmospheric as stopover, wintering, and breeding grounds locations. Administration (www.wpc.ncep.noaa.gov/dailywxmap/ Four Tutakoke units (three males and one female) failed index.html) and WeatherSpark (www.weatherspark.com). or were damaged prior to spring migration and thus did We then assessed the most likely effect of shading based not provide information on northbound migration back to on weather patterns to look for the least displaced lati- Tutakoke. tude of the fix cluster (the most northerly point between Individuals whose geolocators were recovered in a March and September and most southerly point between subsequent year did not differ in mass (Table 2) or body September and March [22]. We also used Google Earth condition (A. Taylor, pers. obs.) at capture compared to all to refine stopover locations using the orientation of the individuals captured at breeding or wintering sites. Birds coastline and our knowledge of habitat use and require- captured at wintering sites were slightly lighter than birds ments (for example, Black Turnstones are almost always captured at breeding sites, but this difference was not sig- found close to rocky intertidal habitat or on man-made nificant (Table 2). We only sexed individuals whose geo- structures such as docks or jetties [5]. locators were recovered in a subsequent year; within this group, females were significantly heavier at initial capture than males (t-test pooled across all sites: t=6.75, df=22, 2.4 Surveys at Northern Montague Island p<0.001; Table 2). However, when pooled across sexes, the initial mass of individuals whose geolocators were later We investigated the presence of Black Turnstones in recovered was not different than that of all individuals Prince William Sound using boat surveys during the peak captured (121.2 ± 9.5 g). of spring migration in 2015. We specifically surveyed areas previously known to have high densities of roosting and foraging birds in the vicinity of northern Montague Island 3.1 Migration Routes and Stopovers from 30 April-6 May 2015. We also recorded any turnstones observed during a test survey on 27-28 April 2015. For all Routes were similar for northbound (Fig. 2) and south- boat surveys, observers surveyed rocky intertidal habitat bound (Fig. 3) migration, with turnstones following the favored by turnstones from the deck of an 11.9-m boat that Outer Coast and Inside Passage coastlines of Alaska and remained within 20 m of the shoreline during surveys. British Columbia in both spring and fall seasons. The error Using Geolocator Data to Address Changes in Migration Patterns for Black Turnstone 5 Table 1. Number of geolocators deployed and recovered at two breeding sites and a wintering site, and the number of individuals tracked on northbound (NB) and southbound (SB) migration by sex. Most individuals were tracked on both northbound and southbound migration, thus the number of each sex tracked on each migration sums to more than the number of geolocators recovered at each site. Males Females Capture Location Recovered NB SB NB SB Alaska Breeding Tutakoke 19* 8 11 6** 7** Cape Krusenstern 2 2 2 - - Washington Wintering Oak Harbor 3 2 2 1 1 Total 24* 12 15 7 8 *data from one geolocator were not usable so data presented are for 23 individuals across all sites **includes two southbound migrations for a single Tutakoke female Alaska, west of the Aleutian Range, with 3 of the 5 stop- Table 2. Mass of Black Turnstones fitted with geolocators (pooled overs occurring around the Lake Iliamna and Lake Clark across capture sites) compared to mass of all individuals captured area. No birds were recorded stopping at or around the at breeding and wintering sites during fieldwork in 2011-2014 to deploy and recover geolocators. historically important northern Montague Island stopover site, although one turnstone stopped at the southern tip Group (n) Weight (g) of Montague Island. Note that for all maps, locations indi- cated by colored symbols are approximate and subject to Geolocator-tagged individuals error estimates as described above. Males (16) 116.2 ± 7.0 Females (8) 131.3 ± 3.9 3.2 Migration Timing and Duration All captured individuals Tutakoke 2013-2014 (109) 122.1 ± 8.3 Black Turnstones departed the western Alaska breeding grounds in mid-July (range: July 1-24) and moved rapidly Cape Krusenstern 2012-2013 (22) 120.9 ± 10.2 to wintering areas along the North Pacific coast, arriving in late July or early August (mean arrival date = 21 July ± Oak Harbor 2011-2013 (42) 118.5 ± 8.5 5.3 days; range: 9 July - 2 August). Southbound migration lasted an average of 5.4 days (range = 0.6–15 d) for all 23 around each point location was on average ~51 km lon- tracked turnstones. In spring, the average departure date gitude (range= 1–320 km) and ~153 km latitude (range= from the wintering grounds was 1 May ± 5.6 days (range: 7–800 km). 19 April – 9 May; n=19). All birds arrived back to the breed- We identified two high-use regions during migration: ing grounds by mid-May (mean arrival date = 12 May ± 3.1 1) western Cook Inlet/Shelikof Strait, Alaska, and 2) the days; range: 5 May – 20 May; n=20). Northbound migration Alexander Archipelago in coastal southeastern Alaska lasted 10.8 days on average (range = 0.6 – 23 days; n=19), plus the Haida Gwaii Archipelago in British Columbia, approximately double that of southbound migration. We and their associated mainland coastlines. Both areas were found no significant sex-specific differences in duration of frequented by turnstones consistently during spring and either northbound or southbound migration (NB: t=0.90, fall migration (Fig. 4). In the Alexander and Haida Gwaii df=10, p=0.39; SB: t=-0.72, df=17, p=0.48). Archipelagos region alone, Black Turnstones made 17 of 31 While migrating, turnstones made relatively short (55%) northbound and 8 of 20 (40%) southbound migra- “hopping” flights along the coast, stopping between tory stops. Of 51 migration stopover locations in total, flights for 3.9 days on average (range = 1.5–15 days). Turn- only 5 (9.8%) occurred in interior locations away from the stones were more likely to stopover on northbound migra- coastline: 3 during northbound and 2 during southbound tion than on southbound migration, and the number of migration. These interior stopover sites all occurred in stopovers made by females vs. males were similar in each 6 Taylor et al. Figure 4. Comparison of stopover locations for Black Turnstones fitted with light-level geolocators, 2011-2015. High-use areas during Figure 2. Northbound migration routes of Black Turnstones tracked migration are circled in white: 1 = western Cook Inlet/Shelikof Strait, with light-level geolocators between 2011 and 2015. A stopover was 2 = the Alexander Archipelago in coastal southeastern Alaska, the defined as a site where an individual stopped for at least 36 hours. Haida Gwaii Archipelago in British Columbia, and their associated Thin gray lines represent great-circle routes between stops whereas mainland coastlines. A stopover was defined as a site where an dark blue lines represent theorized “average” migration routes individual stopped for at least 36 hours. for northbound Black Turnstones based on individual stopover locations and coastal topography. The number of tagged turnstones direction (northbound: 7 females made 15 stops and 9 likely taking each leg of the theorized route is indicated by the thick- males made 16 stops; southbound: 8 females made 8 stops ness of the dark blue line. and 9 males made 12 stops). However, a larger proportion of females than males stopped during both northbound and southbound migration: 7 of 8 (88%) females stopped over during northbound and 8 of 8 (100%) stopped over going southbound (including the single female for which we have two years of data), whereas only 9 of 15 (60%) males stopped on either north or southbound migration. Four individuals moved to wintering areas within 36 hours of their departure from the breeding grounds without stopping at an intermediate location; all of these individ- uals wintered in Alaska. These included the female tagged at Tutakoke whose geolocator was recovered in 2015 and therefore provided two years of migration data: she moved to her wintering area within 24 hours of departing Tutakoke in 2013 but took three days to complete south- bound migration in 2014. In 2015, she migrated back to the breeding grounds without stopping, as did one other turnstone, a male which had also migrated south in less Figure 3. Southbound migration routes of Black Turnstones tracked than 36 hours. with light-level geolocators between 2011 and 2015. A stopover was Black Turnstones stopped for >7 days (defined as defined as a site where an individual stopped for at least 36 hours. staging) eight times during our study. Staging events were Thin gray lines represent great-circle routes between stops whereas evenly split between females and males, but seven of dark blue lines represent theorized “average” migration routes eight were on northbound migration. Females tended to for southbound Black Turnstones based on individual stopover stage for longer than males (10 ± 3.6 days vs. 8.5 ±1.7 days; locations and coastal topography. The number of tagged turnstones likely taking each leg of the theorized route is indicated by the thick- n=4 for both sexes) but the difference was not significant. ness of the dark blue line. Staging areas were located primarily on islands in south- Using Geolocator Data to Address Changes in Migration Patterns for Black Turnstone 7 eastern Alaska’s Alexander Archipelago (Prince of Wales 535.6 km of survey effort in and around northern Montague and Baranof Islands) and on the Haida Gwaii Archipelago Island. In addition, turnstone habitat in Prince William in British Columbia. Sound was scouted by boat on 27 and 28 April 2015 to test survey methodology; on these days 107 Black Turnstones were observed during 140.2 km of survey effort. Despite 3.3 Wintering Locations and Migratory a total of 8.4 km-days of Pacific Herring spawn being observed along the shores of northern Montague Island Connectivity during aerial flights by the Alaska Department of Fish and Wintering locations of Black Turnstones in our study Game on 27 April and 4 May 2015 [23], the boat survey crew spanned 18 degrees of latitude (43–61°N) from the south- did not observe an increase in the number of Black Turn- ern Oregon coast to southcentral Alaska's Kenai Peninsula stones using these areas either during or directly after the (Fig. 2 and 3). The average distance between breeding and spawn events. wintering locations across all tagged individuals was 835 ± 504 km. Of the 20 birds tagged at Alaskan breeding areas, 4 Discussion the majority (70%, n=14) wintered on or between British Columbia’s Haida Gwaii Archipelago and southeastern Alaska’s Alexander Archipelago (corresponding to our 4.1 Migratory and Wintering Patterns and high-use area 2, Fig. 4). Wintering areas in this region Migratory Connectivity tended to be located farther inland than migration stopo- vers, corresponding to greater use of Inside Passage than Our geolocator data identified the Alexander Archipelago Outer Coast locations (Figs. 2 and 3). Another five birds in southeastern Alaska and the Haida Gwaii Archipelago wintered in the Pacific Northwest: three on the outer coast in British Columbia, along with their associated mainland of Vancouver Island, one in the northern Puget Sound/ coastlines, as an important region for Black Turnstones. San Juan Islands area of Washington State, and one on Seventy percent of the birds we tagged at Alaskan breed- the southern coast of Oregon. The female tagged at Tut- ing areas overwintered in this area, and almost half of all akoke whose geolocator provided 2 full years of location stopovers during migration occurred here. Both the Alex- data wintered on the Kenai Peninsula, Alaska, in both ander and Haida Gwaii Archipelagos are characterized by years. There was no significant difference (t=-0.41, df=9, long, inaccessible rocky shorelines with minimal human p=0.69) in the mean wintering latitude for females vs. infrastructure or activity. As a result, historic observations males tagged at Alaskan breeding areas: the mean winter- of turnstones are available from only a few locations in ing latitude for both sexes was the north end of the Haida this region. In the Alexander Archipelago, Black Turn- Gwaii Archipelago. stones were recorded as common during winter in the While the birds tagged at Tutakoke wintered through- early 1900’s at Prince of Wales and Wrangel Islands [24, out the range, the two turnstones tagged on the breeding 25], while at the Haida Gwaii Archipelago, 2000-3000 grounds at Cape Krusenstern wintered on the Haida Gwaii turnstones were estimated to be migrating through the Archipelago in British Columbia and on Admiralty Island, area between 30 April and 11 May 1935 [26]. In more recent Alaska (high-use area 2). The breeding locations of the decades, eBird sightings [27], Christmas Bird Count data three wintering turnstones captured at Oak Harbor, Wash- [28], and observations made during the British Columbia ington, were on the central coast of the Yukon Kuskokwim Coastal Waterbird Survey [29] documented flocks of Black Delta, where the Tutakoke breeding site is located. One Turnstones during the nonbreeding season (late August Oak Harbor individual spent the summer at the Tutakoke through mid-April). At Haida Gwaii, winter flocks often study site, while the individual that nested furthest from number between 100-300 birds [27, 29]. Near major com- Tutakoke was estimated to be 145 km away. munities on the inner coast of the Alexander Archipelago, wintering flocks numbering between 100-400 are regu- larly recorded, although as many as 1400 and 2000 birds 3.4 Turnstone Abundance in Prince William have been recorded during October at Juneau and Peters- burg, respectively. In both archipelagos, flocks numbering Sound >500 have been commonly observed during spring and During the boat survey conducted between 30 April and fall migration in both the protected waters of the Inside 6 May 2015, 765 Black Turnstones were observed during Passage and at more wave-splashed Outer Coast locations 8 Taylor et al. [27]. These observations underscore our geolocator results mid-point. However, the increasing popularity and utility that Black Turnstones migrate and winter along the outer of citizen science programs like eBird and the Christmas as well as the inner coast of both archipelagos and the Bird Count [33] may obscure true trends in the distribution mainland coastline. and abundance of Black Turnstones in the winter in the Our study also highlights for the first time the impor- Pacific Northwest (where the human population is also tance of western Cook Inlet/Shelikof Strait as both a increasing rapidly), because more people are now making northbound and southbound migration stopover area. and recording observations in places where few people Movements by geolocator-tagged birds revealed that Black were recording data in earlier decades. This phenomenon Turnstones did not follow the outer coastline between the has not been studied scientifically, therefore we cannot breeding grounds and this stopover area. Instead, turn- estimate the magnitude of its possible effect on our under- stones flew directly over interior habitats, including the standing of turnstone migration patterns. Aleutian Range, when en route to and from the Tutakoke If turnstones are indeed more likely to be found win- and Cape Krusenstern breeding grounds. None of our geo- tering in the northern half of their nonbreeding range, this locator-tagged birds stopped along the western coastline pattern may be reflective of shorter and warmer winters of the Alaska Peninsula, although eBird sightings and in the Pacific Northwest. Widespread seasonal warming other historic accounts have regularly recorded south- trends were reported from the early twentieth century bound flocks of turnstones stopping along the eastern through 2012 for the U.S. Pacific Northwest (Washing- coastline of Bristol Bay from Ugashik (Pilot Station) to ton, Oregon, Idaho, and western Montana and Wyoming) Naknek [27, 30]. We suggest that for turnstones traversing that included a longer frost-free season by approximately the 600-700 km distance to or from the breeding grounds, two weeks since 1920, and increasing temperatures for the Cook Inlet/Shelikof Strait coastline, the eastern coast- the coldest night each winter [34]. Winter (Dec-Jan-Feb) line of Bristol Bay, and the large lakes on the west side temperatures in the Alaska Panhandle, Northeast Gulf of of the Aleutian Range represent the first suitable stop- Alaska, and Cook Inlet regions (comprising the coastal over (for southbound migrants departing the breeding areas of southeastern Alaska to our designated high-use grounds) or the last suitable stopover (for northbound area of Cook Inlet/Shelikof Strait) exhibited an average migrants heading to the breeding grounds) before they increase of 2.1 to 3.3°C over the period 1949-2012 [35]. Spe- must traverse an area that lacks their preferred high-en- cifically, for Cook Inlet, Alaska, where one of the geolo- ergy rocky or sandy shoreline habitat [5]. cator birds wintered in two consecutive winters, climate Interestingly, none of our geolocator-tagged turn- model projections predict future temperatures increasing stones wintered south of coastal Oregon despite their as much as 4°C during the winter months, resulting in documented winter range extending south into Mexico less snowfall and more rainfall [36]. Taken together, this [5] and previous band resighting data specifically linking evidence suggests that Black Turnstones may be able to the Tutakoke breeding site with a wintering site at Laguna winter farther north today than in previous decades, and Beach, CA [31]. An examination of data segmented by that this trend may continue in and around areas such as 10-year intervals in the eBird database [27] suggests that southeastern Alaska, Cook Inlet, and Kodiak Island. Black Turnstones are wintering farther north each decade; The phenomenon of shortening migration distance for example, 1980-1990 shows few individuals wintering is thought to be a climate-driven response in numerous north of Vancouver Island whereas 2011-2021 shows indi- other avian species: European Greylag Geese, another viduals wintering all the way into Southeast Alaska (~750 short-distance migrant, have significantly decreased km farther north). eBird and Christmas Bird Count records their migration distance over the last 60 years, and the indicate that flocks >200 birds have rarely been recorded average migration distance of this population was shorter over the past several decades in California, while large in milder winters [37]. The benefits of a shorter migration flocks regularly occurred during the winter in Washington, distance may include reduced mortality during migra- British Columbia, and southeast Alaska during the same tion, and birds arriving earlier or in better body condition time period [27, 28]. Pyle and DeSante [32] reported a sig- to breeding territories [38, 39]. Earlier arrival to breeding nificant decline in turnstone numbers on Southeast Far- grounds may allow individuals to choose more suita- allon Island, CA, during the nonbreeding season between ble habitats, which can lead to a consequent increase in breeding success (e.g. [40, 41]). Black Turnstones have 1974 and 1993, although Christmas Bird Count trends were the advantage of being relatively short-distance, short- variable along the adjacent mainland coast. It is possible hop migrants, and most of their Pacific Coast migration that California may now represent the southern edge of route provides suitable wintering habitat. For this species, the Black Turnstone nonbreeding range rather than the Using Geolocator Data to Address Changes in Migration Patterns for Black Turnstone 9 shortening their migration distance in response to climate After arriving on the breeding grounds, Arctic-nesting change could be an easily realized strategy that has the shorebirds rely on local food resources and must time potential to increase overall fitness. their arrival to coincide with the availability of snow-free Our estimates of error in the location data, used to habitat [43]. Therefore, turnstones may be constrained assess migration routes and stopover sites described in terms of earlier arrival to the breeding grounds, and above, were based on post-deployment calibration proce- thus in the speed of northbound migration, by snow dures, which comprise relocations of individuals prior to and inclement weather at their western Alaska breeding departure from a known capture site and after arrival back areas in early May. Long-term monitoring of migration at at that capture site the following year [22]. In addition to several field sites on the central Yukon-Kuskokwim Delta weather conditions, error in location estimates can be (close to our Tutakoke breeding site) indicated that shore- caused by shading of the geolocator due to steep terrain, bird arrival was highly correlated with the timing of the habitat characteristics (e.g., thick or tall vegetation), indi- break-up of ice on the Kashunuk River, which varied by vidual behavior (e.g., the bird facing away from the sun), year but did not advance significantly during the years of or the presence of feathers over the sensor [22]. Shading the study (1977-2008) [44]. was determined to cause error in location estimates for In contrast to northbound migration, southbound many of the geolocators deployed in our study in 2013. In migration is often more flexible, as it is less constrained contrast, there was almost no shading error detected in by weather conditions and food resources as birds fly analysis of data from the geolocators deployed in 2011. south. Additionally, many shorebird species time their An additional source of error related to understand- southbound migration to stay ahead of the migration of ing stopover sites and duration of their use was related to avian predators [45, 46]. Four species of waders of varying our definition of a stopover site (three consecutive fixes overall migration lengths generally took longer to migrate spanning ~36 hours). It is possible that some individuals in fall but flew faster speeds; the difference in migration stopped for <36 hours and therefore these stopover loca- duration stemmed from a tendency to take longer stop- tions were not recognized as such during data analysis. overs going south [47]. Stopover lengths for Black Turn- stones in our study were slightly but non-significantly longer going northbound, and birds were more likely to 4.2 Migration Timing and Duration stopover and to stage (stopover > seven days) on north- bound migration, possibly because it is advantageous to Although the time spent on either migration was relatively move more slowly in the spring while waiting to receive short, Black Turnstones took twice as long to migrate north cues regarding conditions on the breeding grounds. than south, which is unusual for shorebirds (see congener Black Turnstones have a relatively short migration length Ruddy Turnstone, [42]). It is unclear whether this differ- overall: the distance from Haida Gwaii to Tutakoke is ence in migration timing is typical of Black Turnstone approximately 2200 km, which is substantially shorter migration in general, because there is a dearth of infor- than the ~5000 km species considered “short-distance” mation on the timing of individual turnstones’ migration migrants in [47]. Faster migration speeds in the fall, fewer with which to compare our results. A single male Black compelling reasons to stopover, and a relatively short dis- Turnstone banded at the Tutakoke breeding area in spring tance to migrate (that may be getting shorter with climate 1978 was observed multiple times each winter at Laguna change) lead us to predict that southbound migration Beach, CA, during the non-breeding seasons of 1978-1982 duration for Black Turnstones may continue to decrease [31]. Because the end points of this individual’s migration in the future. were known, investigators were able to record approxi- However, the pattern we observed (of shorter migra- mate dates of departure and arrival at each site. In some tion duration in fall than in spring) may have a more years but not all, this individual’s southbound migration localized cause, given that the majority of our estimates of appeared to be faster than its northbound (similar to southbound migration duration were derived from geolo- what we found), although not knowing the exact dates of cators deployed at the Tutakoke site in 2013. The breeding departure and arrival prevented a precise calculation of season of 2013 was unusual on the central Yukon-Kus- migration duration in any one year. kokwim Delta: it was a cold, late spring with snow cover If warming conditions along the Pacific coast migra- remaining until early June and the breakup of river ice tion route have enabled Black Turnstones to shorten their occurring 18 days later than the 1985-2012 average for the migration length, one result could be increasingly shorter region [48]. Many bird species at Tutakoke initiated nests migration durations in the fall but not in the spring. later than average, including Black Turnstones. Then on 10 Taylor et al. 29 June 2013, there was a significant flood event on the after, for a variety of reasons likely including the Exxon Bering Sea coast in the vicinity of the Tutakoke site [48], Valdez oil spill, infectious disease, poor nutrition, and which corresponded to the average predicted hatch date overexploitation by the fishing industry [51]. As a result, of the turnstones captured at Tutakoke during our geolo- during the 1980s and most of the 1990s the average spawn cator deployment effort. Many turnstones would have lost deposition around the Montague Island area was ~66 nests or flightless chicks during this event. The late spring km-days per year and may have been a significant and (causing a delayed breeding season) combined with larg- predictable resource for northbound turnstones. After escale nest failure prior to chicks fledging could have 1999, however, spawning around Montague Island stead- hastened southbound migration departure, and therefore ily declined, culminating in the years 2016-2018 when no increased the duration of fall migration, for turnstones spawning activity was recorded [51]. These changes in captured at Tutakoke in 2013. herring spawn availability and distribution may have led to reduced reliance of Black Turnstones on herring spawn in Prince William Sound to fuel northbound migration 4.3 Importance of Prince William Sound as after the late 1990s, and the observed decline in turnstone use of northern Montague Island each spring. Turnstone Migration Stopover reliance on herring spawn at northern Montague Island The observation that initiated this study was a significant during northbound migration may have a temporary reduction in the number of Black Turnstones recorded at pattern exhibited by an opportunistic species to take northern Montague Island (an Important Bird Area for the advantage of an ephemeral resource, rather than herring species) during the spring of 2010 compared to previous spawn being the primary driver of turnstone distribution observations in the late 1990s [12]. During our 2011-2015 during migration, and Montague Island being a critical geolocator study, <10% of Black Turnstone stopovers (5 of stopover for the population. We also acknowledge that we 51) were recorded in the vicinity of Prince William Sound, do not know whether we sampled a portion of the Black and no birds stopped over at northern Montague Island. Turnstone breeding population that would have stopped This, in addition to the diversity of stopover sites we did over at northern Montague Island in the past, or if there is observe, suggests that northern Montague Island is not an some portion of the population that never used this area obligate stopover and birds are using alternative stopover as a stopover site. To our knowledge, there has been no sites on northbound migration. research done on population structuring in this species We additionally suggest that turnstones are flexible that would help illuminate this distinction. and opportunistic in their choice of stopover sites and are not reliant on herring spawn to continue their northbound migration. Herring spawn each year from mid-March 4.4 Conservation Implications and Future through early May from Puget Sound, WA/Vancouver Directions Island, BC to the northern end of Alexander Archipelago in southeastern Alaska [49, 50]. Despite the presence and Our examination of Black Turnstone migration routes abundance of herring spawn during the same months and duration has provided insight into broad patterns that Black Turnstones are migrating north through these of migratory routing, duration, and connectivity for this areas, reports of turnstones foraging on spawn are lacking charismatic rocky coast shorebird. In particular, geoloca- except from northern Montague Island in Prince William tor-derived location estimates confirmed a changed reli- Sound. Additionally, while previous diet studies at Mon- ance on the Prince William Sound/northern Montague tague Island in the early 1990s found that herring spawn Island area during spring migration, and documented sig- formed an important component of the diet of migrating nificant use of the western Cook Inlet area and the Alex- turnstones, individuals also exhibited a varied diet that ander and Haida Gwaii Archipelagoes by both migrating included mussels and barnacles, and no spawn was found and wintering birds, including that some individuals may in the gut contents of 31% of the turnstones collected [11]. be using the latter area for staging on northbound migra- Similar to other areas along the Pacific Northwest, tion. Matching our geolocator data with citizen science herring spawn in Prince William Sound has historically efforts such as eBird, Christmas Bird Count, and the been an ephemeral resource characterized by dramatic British Columbia Coastal Waterbird Survey makes obvious fluctuations in timing and quantity [51]. In particular, the the need for focused surveys for Black Turnstones during herring population in Prince William Sound expanded the non-breeding period in more remote parts of our doc- and peaked around 1988 and declined significantly there- umented high-use areas, as these areas have not histor- Using Geolocator Data to Address Changes in Migration Patterns for Black Turnstone 11 ically been visited frequently in the winter and casual YDNWR, and River Gates and Megan Boldenow at MBM observations are rare. Focused surveys could help deter- for logistical help in the field. We are grateful to Ptarmigan mine whether there are specific locations within these Air and YDNWR pilots and boat captains, especially Mark high-use areas that should be recognized as important for Agimuk, for safe transport to the Tutakoke site, and to migrating or wintering turnstones. Surveys in these areas Eric Sieh (Arctic Backcountry Flying Service) for flights to could also provide further insight into which habitat char- and from the Cape Krusenstern site. Jim Sedinger (Univer- acteristics drive stopover and staging decisions by turn- sity of Nevada, Reno) and his brant field crew, especially stones. Such surveys done in conjunction with the use of graduate students Alan Leach and Thomas Riecke, kindly smaller GPS tags that have been recently developed for shared their knowledge, their weatherport, and their migration tracking could reduce the error associated with sauna while we were all in the field at Tutakoke together our assessment of migration routes and stopovers, and in the exceptionally cold spring of 2013. We appreciate the further assist with understanding important use areas for Oak Harbor Marina allowing us to capture and tag birds turnstones during the non-breeding season. on their docks for several springs and for fielding boaters’ Additional information is also needed to understand questions along the way. Much gratitude is due Dorn Van the population-level significance of our findings regard- Dommelen (University of Alaska Anchorage), who created ing changing patterns of stopover and wintering site many versions of Figures 2 and 3 in response to our abundance. For example, it is unclear from our study numerous requests for updates. Lastly, we are indebted to where turnstones wintering in the southern half of the our field technicians who spent long hours in inclement non-breeding range (south of Oregon) are nesting. And weather trying to capture turnstones: Tesia Forstner and while current population estimates do not indicate a sig- Jessica Stocking at Tutakoke; Robin Hunnewell, Megan nificant change in the breeding population size for Black Boldenow, and the ASDN crew at Cape Krusenstern; and Turnstones (95,000 individuals in 1992 [4] vs. 135,859 Julie Morse, Dee Taylor, Allen Hebert, and members of the individuals currently [95% LCL = 87,603, 95% UCL = Whidbey Island Audubon Society at Oak Harbor. 184,115; J. Lyons et al., unpubl data.]), the central coast of the Yukon-Kuskokwim Delta is experiencing a loss of the low-lying sedge meadows favored as nesting habitat References by Black Turnstones [6]. 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Journal
Animal Migration – de Gruyter
Published: Jan 1, 2022
Keywords: Short-distance migrant; Rocky coast shorebird; Alaska; Pacific Northwest; Warming winters