Shorebirds typically spend more time fueling and refueling during migration than they spend in actual flight, and consequently their stopover ecology has important implications for fitness and conservation. We examined spatial variation and long‐term changes in stopover duration of radio‐tagged western sandpipers Calidris mauri over three decades on the Pacific Coast of North America. Birds were monitored during 10 periods of northward migration at four key stopover regions including: San Francisco Bay, CA; Willapa Bay/Grays Harbor, WA; Vancouver Island/Fraser River Delta, BC; and Copper River Delta, AK. We used Cormack–Jolly–Seber models to estimate the daily probability of staying at a stopover site (φ) corrected for daily detection rates (p) in relation to annual and seasonal variation. Daily probabilities of staying were then used to calculate length of stay (LOS) in days. Mean LOS decreased at stopover sites as birds progressed northward and varied from 23.1 days at San Francisco Bay to 3.6 days at the Copper River Delta. The duration of length of stay did not show a strong temporal trend by year or decade from 1992 to 2022. Effects of covariates on LOS varied by stopover site, with locally tagged birds staying 2 to 4 days longer than birds tagged farther south, females staying longer than males, and LOS being negatively correlated with mass of the bird at the time of capture with lighter birds having a longer LOS. We suggest that western sandpipers on northward migration may be limited in their ability to reduce LOS beyond the current duration over much of northern parts of the Pacific Flyway. Covariate effects demonstrate that stopover decisions of individual birds are impacted by their energy reserves, but stable lengths of stay over three decades suggest that western sandpipers may have limited flexibility to cope with environmental change in the northern part of their migration.

The Qinghai-Tibet Plateau (QTP) wetland ecosystem is undergoing significant changes because of global climate change, which is likely to affect the distribution of waterbirds. To enhance our understanding of these ecosystems and their waterbirds, we used the black-necked crane (Grus nigricollis) as an indicator and examined shifts in the distribution of its suitable habitats. We analyzed field-collected location data and citizen-science data from mid-southern Tibet for 2006 and 2020 and employed the Species Distribution Model (SDM) to assess changes in suitable wintering habitats. Our findings revealed that between 2006 and 2020, suitable habitats for wintering black-necked cranes expanded overall, though some suitable areas were lost. The expansions are mainly distributed around Qinghai Lake and the northern part of the Yunnan-Guizhou Plateau. Notably, the variable importance scores from 70.7% land use and land cover in 2006 to 56.9% in 2020, with climate variables such as G-bio8 and G-bio18 gaining prominence. As the black-necked crane's range expands, there may be an increase in overlap in its wintering areas. We recommend not only strengthening the management of existing protected areas but also enhancing research on habitat connectivity from a Central Asian Flyway perspective to better address the impacts of climate change.

Animal-borne trackers are commonly used to study bird movements, including in long-distance migrants such as shorebirds. Selecting a tracker and attachment method can be daunting, and methodological advancements often have been made by trial and error and conveyed by word of mouth. We synthesized tracking outcomes across 2745 dorsally mounted trackers on 37 shorebird species around the world. We evaluated how attachment method, power source, data retrieval method, relative tracker mass, and biological traits affected success, where success was defined as whether or not each tag deployment reached its expected tracking duration (i.e. all aspects succeeded for the intended duration of the study: attachment, tracking, data acquisition, and bird survival). We conducted separate analyses for tag deployments with remote data retrieval ('remote-upload tag deployments') and those that archived data and had to be recovered ('archival tag deployments'). Among remote-upload tag deployments, those that were a lighter mass relative to the bird, were beyond their first year of production, transmitted data via satellite, or were attached with a leg-loop harness were most often successful at reaching their expected tracking duration. Archival tag deployments were most successful when applied at breeding areas, or when applied to males in any season. Remote-upload tag deployments with solar power, satellite data retrieval, or leg-loop harnesses continued tracking for longer than those with battery power, other types of data retrieval, or glue attachments. However, the majority of tag deployments failed to reach their expected tracking duration (71% of remote-upload, 83% of archival), which could have been due to tracker failure, attachment failure, or bird mortality. Our findings highlight that many tag deployments may fail to meet the goals of a study if tracking duration is crucial. Using our results, we provide guidelines for selecting a tracker and attachment to improve success at meeting study goals.

The 2014−2016 Pacific marine heatwave (PMH) was an intense and prolonged environmental disturbance that significantly disrupted the marine food web, leading to widespread ecological impacts. The PMH contributed to major shifts in species distributions, mass mortalities, and reproductive failures among upper-trophic level species, including a massive die-off of common murres (Uria aalge) in the Gulf of Alaska (GOA). To assess the impact of the PMH on the winter marine bird community in Prince William Sound (PWS), a large embayment in the northern GOA, we analyzed changes in winter marine bird abundance and species composition in a series of bays before and after the PMH. The overall density of winter marine birds decreased and species composition significantly changed in PWS following the PMH. Specifically, common murres, cormorants, and loons decreased from pre-PMH survey densities, while marbled murrelet (Brachyramphus marmoratus) densities increased. The post-PMH increase in marbled murrelets, likely due to immigration, coincided with the rapid growth and spatial expansion in the PWS Pacific herring (Clupea pallasii) young-of-the-year population and with a smaller, 8-month marine heatwave across the northern GOA. We suggest the mass mortality and lack of recovery by the common murre population provided a competitive release enabling murrelets to exploit a growing forage fish population, and that murrelets may be more effective at shifting to warmer-water zooplankton during marine heatwave events. These results highlight the persistent upper-trophic level changes associated with the PMH and provide important insights into the ecological consequences of environmental disturbances. This is increasingly relevant given the predicted increase in frequency and intensity of marine heatwaves.

Background: The geographic expansion and evolution of A/Goose/Guangdong/1/1996(H5N1) (Gs/GD) lineage H5Nx highly pathogenic avian influenza (HPAI) viruses since 1996 have raised awareness of enzootic circulation among migratory birds and the potential for intercontinental transport and spread. Recent Pacific- and Atlantic-route introductions of HPAI to North America were facilitated by avian migration through subarctic zones, specifically Alaska and Iceland. This study aimed to identify recent historical patterns of exposure to HPAI viruses among birds within and migrating through both regions and evaluate how geographic, demographic, and taxonomic differences contribute to exposure risk at two intercontinental staging locations. Methods: During 2010-2019, blood samples were obtained from captured wild migratory seabirds and waterfowl in Alaska and Iceland. All live birds were released following completion of sampling. Sampling date, species, sampling location, and age class was documented for each bird, and sex was documented when possible. Lentiviral pseudoviruses that express the influenza hemagglutinin surface glycoprotein for H5Nx HPAI and H5 low-pathogenicity avian influenza (LPAI) were constructed for use in serological assays to screen for and quantify titers of antibodies against the latter viruses. Data were analyzed to compare (a) categorical baseline ecological traits between Iceland and Alaska, and (b) ecological traits between birds identified to be seropositive and suggestive/seronegative/fully cross-reactive birds to H5Nx HPAI in Iceland and Alaska. Factors associated with seroreactivity to H5Nx HPAI and H5 LPAI were assessed. Results:The seroprevalence of HPAI among birds in both locations was 7.3% (112/1526). Findings reveal variability in seroprevalence by year, higher rates of exposure to H5 LPAI than H5Nx HPAI overall, and significantly more seropositive and suggestive exposure of birds to H5Nx HPAI in Alaska as compared to Iceland. Geographic, demographic, and taxonomic differences contribute to exposure risk between Alaska and Iceland. Most tested birds were immuno-naïve to HPAI in both locations, which indicates many migratory birds in the subarctic are susceptible to HPAI infection, demonstrating substantial risk for intercontinental transmission between Asia, Europe, and North America. Conclusions: Our findings provide further justification for increased viral and serosurveillance in Alaska and Iceland to monitor subarctic movements of migratory birds and intercontinental transmission dynamics of currently circulating and new strains of HPAI globally.

Autonomous underwater vehicles (AUVs) or gliders are increasingly being used with acoustic telemetry to elucidate fish movements while collecting simultaneous environmental data. We assessed the utility of an AUV equipped with an integrated acoustic receiver to detect Pacific herring (Clupea pallasii) in Prince William Sound, AK, USA. A range test evaluated the effect of glider flight characteristics and environmental conditions on the detection efficiency of transmitters at varying depths. While distance from transmitters was the strongest predictor of detections, glider depth had a variable effect on detection efficiency which depended on transmitter depth and dive orientation. The detection efficiency of the glider-mounted acoustic receiver was less affected by wind speed and water level than that of stationary acoustic receivers deployed within the study area. The AUV also performed repeated, adaptive transects in an area of ∼630 km2 area and detected 30 Pacific herring transmitters without a priori knowledge of their locations. Of these herring transmitters, 14 were presumed shed after repeated detections within the same area, and 2 were detected at multiple locations. This study is the first to demonstrate that glider-mounted acoustic receivers have high detection efficiency for transmitters at varying depths and can detect movements of migratory forage fish in large search areas.

The diversity of influenza A viruses (IAV) is primarily hosted by two highly divergent avian orders: Anseriformes (ducks, swans and geese) and Charadriiformes (gulls, terns and shorebirds). Studies of IAV have historically focused on Anseriformes, specifically dabbling ducks, overlooking the diversity of hosts in nature, including gull and goose species that have successfully adapted to human habitats. This study sought to address this imbalance by characterizing spillover dynamics and global transmission patterns of IAV over 10 years at greater taxonomic resolution than previously considered. Furthermore, the circulation of viral subtypes in birds that are either host-adapted (low pathogenic H13, H16) or host-generalist (highly pathogenic avian influenza—HPAI H5) provided a unique opportunity to test and extend models of viral evolution. Using Bayesian phylodynamic modelling we uncovered a complex transmission network that relied on ecologically divergent bird hosts. The generalist subtype, HPAI H5 was driven largely by wild geese and swans that acted as a source for wild ducks, gulls, land birds, and domestic geese. Gulls were responsible for moving HPAI H5 more rapidly than any other host, a finding that may reflect their long-distance, pelagic movements and their immuno-naïve status against this subtype. Wild ducks, long viewed as primary hosts for spillover, occupied an optimal space for viral transmission, contributing to geographic expansion and rapid dispersal of HPAI H5. Evidence of inter-hemispheric dispersal via both the Pacific and Atlantic Rims was detected, supporting surveillance at high latitudes along continental margins to achieve early detection. Both neutral (geographic expansion) and non-neutral (antigenic selection) evolutionary processes were found to shape subtype evolution which manifested as unique geographic hotspots for each subtype at the global scale. This study reveals how a diversity of avian hosts contribute to viral spread and spillover with the potential to improve surveillance in an era of rapid global change.

Black Turnstone is an obligate Pacific coast 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 major spring stopover site, northern Montague Island in Prince William Sound, Alaska, difficult to interpret. We tracked 23 Black Turnstones between breeding and wintering areas and examined migration timing, duration, and routes used. We identified two high-use regions during migration: 1) Cook Inlet/Shelikof Strait, Alaska, and 2) the Haida Gwaii Archipelago in British Columbia/Alexander Archipelago in southeastern Alaska. This second region was also an important wintering area. We found that northbound migration was longer than southbound (the reverse of what is often observed in shorebirds) and that staging behavior was primarily seen during northbound migration. No birds were tracked to northern Montague Island, and only a few individuals stopped anywhere in Prince William Sound. Alterations in patterns of spring herring spawn in Prince William Sound may be affecting the routes and stopovers used by Black Turnstones, and birds may be wintering farther north in recent decades due to warmer winter conditions. Additionally, the increasing availability and popularity of citizen science efforts like eBird has created a mechanism for disseminating observations from less accessible parts of the Black Turnstone range, a fact which may confound our understanding of whether migration routes for this species have changed over the last 30 years.

Comprehensive assessments of cumulative impacts to seabirds have been hindered by an incomplete understanding of temporal and spatial patterns in marine habitat use, particularly during the non-breeding season when seabirds can range widely across the global ocean. Alcids are an important component of the meso-predator biodiversity of the North Pacific Ocean, yet the non-breeding movement ecology and distribution for many of the Pacific Auk species remain poorly quantified. Recent and projected declines for historically robust populations of tufted puffin ( Fratercula cirrhata ) in Alaska highlight the importance of resolving aspects of the species’ non-breeding ecology, especially the pelagic phenology and distribution. We used light-level geolocation to quantify the annual at-sea distribution of tufted puffins between a major Gulf of Alaska nesting colony (Middleton Island) and heretofore unknown migration routes and wintering areas. Geolocator data from 42 complete migration routes of reproductive adult tufted puffins collected primarily between 2018-2020 revealed that both males and females were short-distance migrants, wintering on average 616 km from their breeding colony. Tufted puffins departed the breeding grounds in early September. Males made fewer stops and arrived earlier to wintering areas than females, however the arrival date to the wintering area was later in 2019 compared to 2018. Males took 30.5 ± 16.7 (± standard deviation) days in 2018 and 30.8 ± 24.6 days in 2019 to arrive at wintering areas. Conversely, females took 36.1 ± 16.8 days in 2018 and 59.8 ± 17.3 days in 2019 to arrive at wintering areas. Adult tufted puffins wintered primarily in the deep offshore waters of the eastern Gulf of Alaska and partially in the adjacent Northeast Pacific Ocean over a period of 151.9 days ± 31.6 with spring migrations starting by late March. Males and females showed consistent spatial distributions within seasons, especially during winter. Tufted puffins shifted southwards throughout the non-breeding season, similar to other Atlantic and Northeast Pacific alcids. Our study provides important information on the at-sea non-breeding phenology and distribution of tufted puffins, which can inform risk assessments for the species including vulnerability to spatially and temporally explicit marine pollution, disease, fisheries by-catch, and ocean-climate variability.

Summary Four of China’s six wintering populations of “grey” geese Anser spp. declined during the last decade. In contrast, the Bar-headed Goose A. indicus wintering population in China’s Tibet Autonomous Region more than doubled. During six surveys in Tibet over a 27-year period (1991/92 to 2017/18 winters) we documented an annual growth rate of 6.8% in the Bar-headed Goose population – an increase from approximately 10,100 to 68,100 birds. We propose that in addition to the cessation of hunting, the population growth of Bar-headed Goose is being driven by changes in agricultural land use patterns in Tibet, the establishment of protected areas on the wintering and breeding grounds, and the impacts of climate change across the Tibetan Plateau. Consistent with this hypothesis, the sown area of winter wheat in Tibet has increased and geese have shifted from primarily feeding in crop stubble to planted winter wheat fields. We also found that the most rapid population growth coincided with a 1998 climate regime shift across the Tibetan Plateau resulting in warmer temperatures, an increase in net precipitation, the appearance of new lakes and changes in the water levels and surface area of historical lakes. We suggest that warmer temperatures and high-quality forage on the south-central Tibet wintering grounds may be enhancing over-winter survival, while on the breeding grounds the expansion of lakes and wet meadows is augmenting breeding and brood-rearing habitat.

During the Pacific marine heatwave of 2014–2016, abundance and quality of several key forage fish species in the Gulf of Alaska were simultaneously reduced throughout the system. Capelin ( Mallotus catervarius ), sand lance ( Ammodytes personatus ), and herring ( Clupea pallasii ) populations were at historically low levels, and within this community abrupt declines in portfolio effects identify trophic instability at the onset of the heatwave. Although compensatory changes in age structure, size, growth or energy content of forage fish were observed to varying degrees among all these forage fish, none were able to fully mitigate adverse impacts of the heatwave, which likely included both top‐down and bottom‐up forcing. Notably, changes to the demographic structure of forage fish suggested size‐selective removals typical of top‐down regulation. At the same time, changes in zooplankton communities may have driven bottom‐up regulation as copepod community structure shifted toward smaller, warm water species, and euphausiid biomass was reduced owing to the loss of cold‐water species. Mediated by these impacts on the forage fish community, an unprecedented disruption of the normal pelagic food web was signaled by higher trophic level disruptions during 2015–2016, when seabirds, marine mammals, and groundfish experienced shifts in distribution, mass mortalities, and reproductive failures. Unlike decadal‐scale variability underlying ecosystem regime shifts, the heatwave appeared to temporarily overwhelm the ability of the forage fish community to buffer against changes imposed by warm water anomalies, thereby eliminating any ecological advantages that may have accrued from having a suite of coexisting forage species with differing life‐history compensations.

Some of the longest and most comprehensive marine ecosystem monitoring programs were established in the Gulf of Alaska following the environmental disaster of the Exxon Valdez oil spill over 30 years ago. These monitoring programs have been successful in assessing recovery from oil spill impacts, and their continuation decades later has now provided an unparalleled assessment of ecosystem responses to another newly emerging global threat, marine heatwaves. The 2014–2016 northeast Pacific marine heatwave (PMH) in the Gulf of Alaska was the longest lasting heatwave globally over the past decade, with some cooling, but also continued warm conditions through 2019. Our analysis of 187 time series from primary production to commercial fisheries and nearshore intertidal to offshore oceanic domains demonstrate abrupt changes across trophic levels, with many responses persisting up to at least 5 years after the onset of the heatwave. Furthermore, our suite of metrics showed novel community-level groupings relative to at least a decade prior to the heatwave. Given anticipated increases in marine heatwaves under current climate projections, it remains uncertain when or if the Gulf of Alaska ecosystem will return to a pre-PMH state.

BACKGROUND:Over the past two decades, various species of forage fish have been successfully implanted with miniaturized acoustic transmitters and subsequently monitored using stationary acoustic receivers. When acoustic receivers are configured in an array, information related to fish direction can potentially be determined, depending upon the number and relative orientation of the acoustic receivers. However, it can be difficult to incorporate directional information into frequentist mark-recapture methods. Here we show how an empirical Bayesian approach can be used to develop a model that incorporates directional movement information into the Arnason-Schwarz modeling framework to describe survival and migration patterns of a Pacific herring (Clupea pallasii) population in coastal Alaska, USA.METHODS:We acoustic-tagged 326 adult Pacific herring during April 2017 and 2018 while on their spawning grounds in Prince William Sound Alaska, USA. To monitor their movements, stationary acoustic receivers were deployed at strategic locations throughout the Sound. Receivers located at the major entrances to the Gulf of Alaska were arranged in parallel arrays to determine the directional movements of the fish. Informative priors were used to incorporate the directional information recorded at the entrance arrays into the model.RESULTS:A seasonal migratory pattern was found at one of Prince William Sound's major entrances to the Gulf of Alaska. At this entrance, fish tended to enter the Gulf of Alaska during spring and summer after spawning and return to Prince William Sound during the fall and winter. Fish mortality was higher during spring and summer than fall and winter in both Prince William Sound and the Gulf of Alaska.CONCLUSIONS:An empirical Bayesian modeling approach can be used to extend the Arnason-Schwarz modeling framework to incorporate directional information from acoustic arrays to estimate survival and characterize the timing and direction of migratory movements of forage fish.

Piscivorous groundfish have been implicated as a major hindrance to Pacific herring (Clupea pallasii) population recovery within Prince William Sound, Alaska (PWS); however, the key piscivores have not been identified. To address this knowledge gap, groundfish were collected from PWS herring nursery fjords (2009–2012) during winter, a period when juvenile herring energy levels decrease, suppressing predator avoidance. Three species, Pacific cod (Gadus macrocephalus), walleye pollock (G. chalcogrammus), and big skate (Beringraja binoculata) were identified as key herring consumers based on diet frequency of occurrence. Their stomach contents were examined to document any variability in prey occurrences and to explore whether pollock or other prey types could mediate herring consumption. For Pacific cod, there was strong evidence of seasonality in herring consumption, with herring occurring in 7% and 50% of stomachs in November and March, respectively. Walleye pollock and big skate diets were more influenced by body size and longitude, respectively. Pacific cod consumed notably more adult herring (ages 3+) than the other piscivores, big skate consumed herring ages 3+ and younger, while walleye pollock was a major consumer of age 0 herring. As groundfish body size increased, all three species consumed larger, age 2+ pollock, suggesting pollock presence mediates herring overwintering mortality and that pollock cannibalism is an important dietary pathway in PWS. By identifying the key groundfish consumers of herring and pollock in PWS, and the spatial, temporal, and biological variables that influence the occurrence of these forage fishes in their diets, this research contributes to a larger body of knowledge seeking to explain the mechanisms responsible for their lack of recovery in PWS and offers novel insight into the importance of pollock as a forage fish in PWS.

Despite the importance of understanding marine bird response to prey fish, few studies have examined this relationship during winter. Over a 5-year period, we conducted synoptic marine bird and hydroacoustic forage fish surveys during early (November) and late (March) winter to characterize the factors influencing marine bird and forage fish dynamics at two spatial scales (fish school and bay) within subarctic bays of coastal Alaska, USA. Over 40% of observed marine birds were associated with a fish school (within 150 m of a fish school), although only 20% of fish schools were associated with birds. Seasonally, we recorded significantly more schools during early winter. The marine bird community also shifted from being comprised primarily of marbled murrelets (Brachyramphus marmoratus) and large gulls (Larus spp.) in early winter to common murres (Uria aalge) in late winter. At the school level, marine birds were more likely to be associated with shallow fish schools within 500 m of shore and in smaller prey patches. At the bay level, gull abundance was positively associated with the total number of fish schools recorded, while diving birds were more abundant when fish schools were higher in the water column, in shallower bottom depths, and in areas with more eel grass habitat. Our results indicate the importance of temporal, habitat, and fish school variables as drivers of marine bird presence and abundance, underscoring the complexity of predator-prey dynamics in the marine environment during winter.

North America's northernmost, sizable colony of Caspian Terns (Hydroprogne caspia) is located on the Copper River Delta of south-central Alaska, USA. The colony was monitored in June during 2008-2016 and in July during 2009-2013. This 9-year period coincided with reduction of Caspian Tern nesting habitat at East Sand Island in the Columbia River estuary, Oregon, USA, one of the world's largest Caspian Tern breeding colonies. The number of active nests on the Copper River Delta more than doubled during the early study period from 209 in 2008 to 423 in 2013. However, there was a steady decline in the number of nests during 2014 (281) to 2015 (115) and the colony failed in 2016. These declines were likely due to warm sea surface temperature anomalies across the northeastern Pacific Ocean in those years. Based on resightings of banded individuals, colony connectivity was documented between the Copper River Delta and other colonies, ranging from southeast Alaska (215 km) to central California, USA (>3,000 km). The East Sand Island colony was the most important source of immigrants to the Copper River Delta. While the Copper River Delta now serves as important natural breeding habitat for Caspian Terns, increased flooding and severe storms associated with climate change will likely limit colony size and productivity in the long-term.

The contents of 1056 stomachs were included in a trophic-guild analysis to document separation amongst 16 groundfish species inhabiting Pacific herring Clupea pallasii and walleye pollock Gadus chalcogrammus nursery fjords in Prince William Sound, Alaska and to determine the relative contribution of C. pallasii and G. chalcogrammus to that separation. A total of five multi-species feeding guilds and one outlier species were determined through multivariate analyses. Major gradients of trophic separation spanned from invertebrates (mostly shrimps, crabs and unidentified decapods) to fishes (mostly unidentified fishes, C. pallasii and G. chalcogrammus) a pattern that was influenced by intra and interspecific differences in predator lengths. While C. pallasii and G. chalcogrammus were important to the overall guild structure, within-guild similarities were consistently highest due to unidentified fishes. In general, larger predators consumed the largest C. pallasii and G. chalcogrammus, with the smaller-on-average predators consuming smaller C. pallasii and fewer or smaller G. chalcogrammus. Regardless of guild inclusion, groundfishes primarily consumed pre-recruit C. pallasii and G. chalcogrammus (i.e., younger than age 3 years fishes), which has the potential to negatively influence recruitment of these forage fishes to the adult, spawning population.

Subsistence harvest of wild bird eggs is a traditional activity across many parts of Alaska. We examined the impact of egg collection on Glaucous-winged Gulls Larus glaucescens nesting on Alaska's Copper River Delta by comparing egg laying patterns across two experimental plots. In one plot, we manually removed eggs from incomplete clutches and in the other we walked through the plot to create disturbance. Gulls in this study did not appear to increase the number of eggs laid to compensate for eggs experimentally removed from their nests, with only 10 % of gull pairs completing a full clutch following nest manipulation.