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Conservation status and management priorities are often informed by population trends. Trend estimates can be derived from population surveys or models, but both methods are associated with sources of uncertainty. Many Arctic-breeding shorebirds are thought to be declining based on migration and/or overwintering population surveys, but data are lacking to estimate the trends of some shorebird species. In addition, for most species, little is known about the stage(s) at which population bottlenecks occur, such as breeding vs. nonbreeding periods. We used previously published and unpublished estimates of vital rates to develop the first large-scale population models for 6 species of Arctic-breeding shorebirds in North America, including separate estimates for 3 subspecies of Dunlin. We used the models to estimate population trends and identify life stages at which population growth may be limited. Our model for the arcticola subspecies of Dunlin agreed with previously published information that the subspecies is severely declining. Our results also linked the decline to the subspecies' low annual adult survival rate, thus potentially implicating factors during the nonbreeding period in the East Asian–Australasian Flyway. However, our trend estimates for all species showed high uncertainty, highlighting the need for more accurate and precise estimates of vital rates. Of the vital rates, annual adult survival had the strongest influence on population trend in all taxa. Improving the accuracy, precision, and spatial and temporal coverage of estimates of vital rates, especially annual adult survival, would improve demographic model-based estimates of population trends and help direct management to regions or seasons where birds are subject to higher mortality.LAY SUMMARYDocumenting population trends is essential for evaluating the conservation status of wild species such as Arctic-breeding shorebirds.Trends can be estimated with population surveys or by predicting population growth based on survival rates and fecundity, but both methods are challenging, especially for species with large or remote geographic distributions.We used recent broad-scale estimates of survival and fecundity to develop population models for 6 species of Arctic-breeding shorebirds.The arcticola subspecies of Dunlin is likely in severe decline, but our trend estimates for all species showed high uncertainty.Uncertainty around the values of annual adult survival rates was a key driver of the uncertainty around the trend estimates.Our work highlights the need for better estimates of annual adult survival, seasonal survival, juvenile survival, and breeding propensity for these Arctic-breeding shorebirds.

Many Arctic shorebird populations are declining, and quantifying adult survival and the effects of anthropogenic factors is a crucial step toward a better understanding of population dynamics. We used a recently developed, spatially explicit Cormack–Jolly–Seber model in a Bayesian framework to obtain broad-scale estimates of true annual survival rates for 6 species of shorebirds at 9 breeding sites across the North American Arctic in 2010–2014. We tested for effects of environmental and ecological variables, study site, nest fate, and sex on annual survival rates of each species in the spatially explicit framework, which allowed us to distinguish between effects of variables on site fidelity versus true survival. Our spatially explicit analysis produced estimates of true survival rates that were substantially higher than previously published estimates of apparent survival for most species, ranging from S = 0.72 to 0.98 across 5 species. However, survival was lower for the arcticola subspecies of ...

Semipalmated Sandpiper (Calidris pusilla) populations have undergone significant declines at core nonbreeding sites in northeastern South America. Breeding populations have also declined in the eastern North American Arctic, but appear to be stable or increasing in the central and western Arctic. To identify vulnerable populations and sites, we documented the migratory connectivity of Semipalmated Sandpipers using light-level geolocators, deploying 250 at 8 Arctic sites across the species' breeding range from 2011 to 2015, plus 87 at a single wintering site in northeastern Brazil in 2013 and 2014. We recovered 59 units and resighted 7 more (26% return rate) on the breeding grounds, but none at the nonbreeding site. We recovered only ∼3% of units deployed in 2013 at eastern Arctic breeding sites, but recovered 33% of those deployed in 2015. Overall, birds with geolocators were 57% as likely to return as those carrying alphanumeric flags. Stopover durations at prairie sites (mean: 8.7 days southbou...

Gut microbiota can have important effects on host health, but explanatory factors and pathways that determine gut microbial composition can differ among host lineages. In mammals, host phylogeny is one of the main drivers of gut microbiota, a result of vertical transfer of microbiota during birth. In birds, it is less clear what the drivers might be, but both phylogeny and environmental factors may play a role. We investigated host and environmental factors that underlie variation in gut microbiota composition in eight species of migratory shorebirds. We characterized bacterial communities from 375 fecal samples collected from adults of eight shorebird species captured at a network of nine breeding sites in the Arctic and sub-Arctic ecoregions of North America, by sequencing the V4 region of the bacterial 16S ribosomal RNA gene. Firmicutes (55.4%), Proteobacteria (13.8%), Fusobacteria (10.2%), and Bacteroidetes (8.1%) dominated the gut microbiota of adult shorebirds. Breeding location was the main driver of variation in gut microbiota of breeding shorebirds (R-2 = 11.6%), followed by shorebird host species (R-2 = 1.8%), and sampling year (R-2 = 0.9%), but most variation remained unexplained. Site variation resulted from differences in the core bacterial taxa, whereas rare, lowabundance bacteria drove host species variation. Our study is the first to highlight a greater importance of local environment than phylogeny as a driver of gut microbiota composition in wild, migratory birds under natural conditions. Avian Health Program grants from the U.S. Fish and Wildlife Service [2013-02]; National Science FoundationNational Science Foundation (NSF) [DDIG-1501479]; Arctic Landscape Conservation Cooperative; U.S. Fish and Wildlife ServiceUS Fish & Wildlife Service; Division of Biology at the Kansas State University; Kansas State University Open Access Publishing Fund This work was funded by the Avian Health Program grants from the U.S. Fish and Wildlife Service (to JS and RL, and 2013-02 to KG and RL), a Doctoral Dissertation Improvement Grant from the National Science Foundation (DDIG-1501479 to KG), the Arctic Landscape Conservation Cooperative, the U.S. Fish and Wildlife Service, and the Division of Biology at the Kansas State University. Publication of this article was funded in part by the Kansas State University Open Access Publishing Fund.

Kubelka et al. (Science, 9 November 2018, p. 680-683) claim that climate change has disrupted patterns of nest predation in shorebirds. They report that predation rates have increased since the 1950s, especially in the Arctic. We describe methodological problems with their analyses and argue that there is no solid statistical support for their claims.

Kubelka et al. (Reports, 9 November 2018, p. 680) claim that climate change has disrupted patterns of nest predation in shorebirds. They report that predation rates have increased since the 1950s, especially in the Arctic. We describe methodological problems with their analyses and argue that there is no solid statistical support for their claims. Fil: Bulla, Martin. Nioz Royal Netherlands Institute For Sea Research; Países Bajos. Max Planck Institute For Ornithology; Alemania. Czech University of Life Sciences; República Checa Fil: Reneerkens, Jeroen. Nioz Royal Netherlands Institute For Sea Research; Países Bajos. University of Groningen; Países Bajos Fil: Weiser, Emily L.. Upper Midwest Environmental Sciences Center; Estados Unidos Fil: Sokolov, Aleksandr. Institute Of Plant And Animal Ecology; Rusia Fil: Taylor, Audrey R.. University of Alaska; Estados Unidos Fil: Sittler, Benoît. Albert Ludwigs University of Freiburg; Alemania. Arctic Ecology Research Group; Francia Fil: McCaffery, Brian J.. U.S. Fish and Wildlife Service; Estados Unidos Fil: Ruthrauff, Dan R.. U.S. Geological Survey; Estados Unidos Fil: Catlin, Daniel H.. Virginia Tech University; Estados Unidos Fil: Payer, David C.. National Park Service; Estados Unidos Fil: Ward, David H.. U.S. Geological Survey; Estados Unidos Fil: Solovyeva, Diana V.. Institute of Biological Problems of the North; Rusia Fil: Santos, Eduardo S. A.. Universidade de São Paulo; Brasil Fil: Rakhimberdiev, Eldar. Lomonosov Moscow State University; Rusia. University of Groningen; Países Bajos Fil: Nol, Erica. Trent University; Canadá Fil: Kwon, Eunbi. Virginia Tech; Estados Unidos Fil: Brown, Glen S.. Ministry of Natural Resources and Forestry; Canadá Fil: Hevia, Glenda Denise. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Gates, H. River. National Audubon Society; Estados Unidos Fil: Johnson, James A.. Fish and Wildlife Service; Estados Unidos Fil: van Gils, Jan A.. Department of Coastal Systems and Utrecht University; Países Bajos Fil: Hansen, Jannik. Aarhus University. Aarhus Institute Of Advanced Studies.; Dinamarca Fil: Lamarre, Jean-François. Polar Knowledge Canada; Canadá Fil: Rausch, Jennie. Environment and Climate Change Canada; Canadá Fil: Conklin, Jesse R.. University of Groningen; Países Bajos Fil: Liebezeit, Joe. Audubon Society of Portland; Estados Unidos Fil: Bêty, Joël. University of Quebec; Canadá Fil: Lang, Johannes. Arctic Ecology Research Group ; Francia. Giessen University; Alemania Fil: Alves, José A.. University of Aveiro; Portugal. University of Iceland; Islandia Fil: Fernández-Elipe, Juan. No especifíca; Fil: Exo, Klaus-Michael. Institute of Avian Research “Vogelwarte Helgoland"; Alemania Fil: Bollache, Loïc. Universite de Franche-Comte; Francia Fil: Bertellotti, Néstor Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Giroux, Marie-Andrée. Université de Moncton; Canadá Fil: van de Pol, Martijn. Netherlands Institute of Ecology ; Países Bajos Fil: Johnson, Matthew. USDA Forest Service; Estados Unidos Fil: Boldenow, Megan L.. University of Alaska; Estados Unidos Fil: Valcu, Mihai. Max Planck Institute für Ornithologie; Alemania Fil: Soloviev, Mikhail. Lomonosov Moscow State University; Alemania Fil: Sokolova, Natalya. Arctic Research Station; Rusia Fil: Senner, Nathan R.. University of South Carolina; Estados Unidos Fil: Lecomte, Nicolas. Université de Moncton; Canadá Fil: Meyer, Nicolas. Universite de Franche-Comte; Francia. Arctic Ecology Research Group; Francia Fil: Schmidt, Niels Martin. Aarhus University. Department of Bioscience; Dinamarca Fil: Gilg, Olivier. Arctic Ecology Research Group; Francia. Universite de Franche-Comte; Francia Fil: Smith, Paul A.. Environment and Climate Change Canada; Canadá Fil: Machín, Paula. No especifíca; Fil: McGuire, Rebecca L.. Wildlife Conservation Society; Estados Unidos Fil: Cerboncini, Ricardo A. S.. Universidade Federal do Paraná; Brasil Fil: Ottvall, Richard. No especifíca; Fil: van Bemmelen, Rob S. A.. Wageningen Marine Research; Países Bajos Fil: Swift, Rose J.. Cornell University; Estados Unidos Fil: Saalfeld, Sarah T.. No especifíca; Fil: Jamieson,Sarah E.. Simon Fraser University; Canadá Fil: Brown, Stephen. No especifíca; Fil: Piersma, Theunis. NIOZ Royal Netherlands Institute for Sea Research; Países Bajos. Conservation Ecology Group; Países Bajos Fil: Albrecht, Tomas. Czech Academy of Sciences; República Checa. Charles University; República Checa Fil: D’Amico, Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Lanctot, Richard B.. U.S. Fish and Wildlife Service; Estados Unidos Fil: Kempenaers, Bart. Max Planck Institute für Ornithologie; Alemania

Rapid warming has occurred over the past 50 years in Arctic Alaska, where temperature strongly affects ecological patterns and processes. To document landscape change over a half century in the Arctic National Wildlife Refuge, Alaska, we visually interpreted geomorphic and vegetation changes on time series of coregistered high-resolution imagery. We used aerial photographs for two time periods, 1947–1955 and 1978–1988, and Quick Bird and IKONOS satellite images for a third period, 2000–2007. The stratified random sample had five sites in each of seven ecoregions, with a systematic grid of 100 points per site. At each point in each time period, we recorded vegetation type, microtopography, and surface water. Change types were then assigned based on differences detected between the images. Overall, 23% of the points underwent some type of change over the ~50-year study period. Weighted by area of each ecoregion, we estimated that 18% of the Refuge had changed. The most common changes were wildfire and postfire succession, shrub and tree increase in the absence of fire, river erosion and deposition, and ice-wedge degradation. Ice-wedge degradation occurred mainly in the Tundra Biome, shrub increase and river changes in the Mountain Biome, and fire and postfire succession in the Boreal Biome. Changes in the Tundra Biome tended to be related to landscape wetting, mainly from increased wet troughs caused by ice-wedge degradation. The Boreal Biome tended to have changes associated with landscape drying, including recent wildfire, lake area decrease, and land surface drying. The second time interval, after ~1982, coincided with accelerated climate warming and had slightly greater rates of change.

The Arctic is experiencing rapidly warming conditions, increasing predator abundance, and diminishing population cycles of keystone species such as lemmings. However, it is still not known how many Arctic animals will respond to a changing climate with altered trophic interactions. We studied clutch size, incubation duration and nest survival of 17 taxa of Arctic-breeding shorebirds at 16 field sites over 7years. We predicted that physiological benefits of higher temperatures and earlier snowmelt would increase reproductive effort and nest survival, and we expected increasing predator abundance and decreasing abundance of alternative prey (arvicoline rodents) to have a negative effect on reproduction. Although we observed wide ranges of conditions during our study, we found no effects of covariates on reproductive traits in 12 of 17 taxa. In the remaining taxa, most relationships agreed with our predictions. Earlier snowmelt increased the probability of laying a full clutch from 0.61 to 0.91 for Western Sandpipers, and shortened incubation by 1.42days for arcticola Dunlin and 0.77days for Red Phalaropes. Higher temperatures increased the probability of a full clutch from 0.60 to 0.93 for Western Sandpipers and from 0.76 to 0.97 for Red-necked Phalaropes, and increased daily nest survival rates from 0.9634 to 0.9890 for Semipalmated Sandpipers and 0.9546 to 0.9880 for Western Sandpipers. Higher abundance of predators (foxes) reduced daily nest survival rates only in Western Sandpipers (0.9821-0.9031). In contrast to our predictions, the probability of a full clutch was lowest (0.83) for Semipalmated Sandpipers at moderate abundance of alternative prey, rather than low abundance (0.90). Our findings suggest that in the short-term, climate warming may have neutral or positive effects on the nesting cycle of most Arctic-breeding shorebirds. National Fish and Wildlife Foundation [2010-0061-015, 2011-0032-014, 0801.12.032731, 0801.13.041129]; Neotropical Migratory Bird Conservation Act [F11AP01040, F12AP00734, F13APO535, 4073]; Arctic Goose Joint Venture; Arctic National Wildlife Refuge; BP Exploration (Alaska) Inc.; Bureau of Land Management; Canada Fund for InnovationCanada Foundation for Innovation; Canada Research ChairsCanada Research Chairs; Cape Krusenstern National Monument grant; Centre for Wildlife Ecology at Simon Fraser University; Churchill Northern Studies Centre; Cornell University Graduate School Mellon Grant; Ducks Unlimited Canada; Environment and Climate Change Canada; FQRNT (Quebec)FQRNT; Government of Nunavut; Indigenous and Northern Affairs Canada; Kansas State University; Kresge Foundation; Liz Claiborne and Art Ortenberg Foundation; Manomet Center for Conservation Sciences; Mississippi Flyway Council; Murie Science and Learning Center grants; National Fish and Wildlife Foundation; National Park Service; National Science Foundation (Office of Polar Programs Grant) [ARC-1023396]; National Science Foundation (Doctoral Dissertation Improvement Grant)National Science Foundation (NSF) [1110444]; Natural Resources Canada (Polar Continental Shelf Program); Natural Sciences and Engineering Research Council of CanadaNatural Sciences and Engineering Research Council of Canada; Northern Studies Training Program; Selawik National Wildlife Refuge; Trust for Mutual Understanding; Universite du Quebec a Rimouski; University of Alaska Fairbanks; University of Colorado Denver; University of Missouri Columbia; University of Moncton; US Fish and Wildlife Service (Migratory Bird Management Division, Survey, Monitoring and Assessment Program); US Fish and Wildlife Service (Alaska National Wildlife Refuge System's Challenge Cost Share Program); US Fish and Wildlife Service (Avian Influenza Health and Influenza programmes); US Geological Survey (USGS) (Changing Arctic Ecosystem Initiative, Wildlife Program of the USGS Ecosystem Mission Area); W. Garfield Weston Foundation; Alaska Department of Fish and Game E.L.W compiled the field data, designed and performed the statistical analyses and wrote the manuscript. B.K.S. assisted with design of analyses and preparation of the manuscript. R.B.L., S.C.B. and H.R.G. led development of standardized field protocols and coordinated field work. B.K.S., R.B.L., S.C.B., H.R.G. and all other authors, who are listed in alphabetical order, designed and conducted the field studies, contributed to interpreting the results and assisted with editing the manuscript. Major support for the ASDN was provided by the National Fish and Wildlife Foundation (grants 2010-0061-015, 2011-0032-014, 0801.12.032731 and 0801.13.041129), the Neotropical Migratory Bird Conservation Act (grants F11AP01040, F12AP00734 and F13APO535) and the Arctic Landscape Conservation Cooperative. Additional funding for participating field sites was provided by: Alaska Department of Fish and Game, Arctic Goose Joint Venture, Arctic National Wildlife Refuge, BP Exploration (Alaska) Inc., Bureau of Land Management, Canada Fund for Innovation, Canada Research Chairs, Cape Krusenstern National Monument grant, Centre for Wildlife Ecology at Simon Fraser University, Churchill Northern Studies Centre, Cornell University Graduate School Mellon Grant, Ducks Unlimited Canada, Environment and Climate Change Canada, FQRNT (Quebec), Government of Nunavut, Indigenous and Northern Affairs Canada, Kansas State University, Kresge Foundation, Liz Claiborne and Art Ortenberg Foundation, Manomet Center for Conservation Sciences, Mississippi Flyway Council, Murie Science and Learning Center grants, National Fish and Wildlife Foundation, National Park Service, National Science Foundation (Office of Polar Programs Grant ARC-1023396 and Doctoral Dissertation Improvement Grant 1110444), Natural Resources Canada (Polar Continental Shelf Program), Natural Sciences and Engineering Research Council of Canada (Discovery Grant and Northern Supplement), Neotropical Migratory Bird Conservation Act (grant 4073), Northern Studies Training Program, Selawik National Wildlife Refuge, Trust for Mutual Understanding, Universite du Quebec a Rimouski, University of Alaska Fairbanks, University of Colorado Denver, University of Missouri Columbia, University of Moncton, US Fish and Wildlife Service (Migratory Bird Management Division, Survey, Monitoring and Assessment Program, Alaska National Wildlife Refuge System's Challenge Cost Share Program and Avian Influenza Health and Influenza programmes), US Geological Survey (USGS) (Changing Arctic Ecosystem Initiative, Wildlife Program of the USGS Ecosystem Mission Area), and the W. Garfield Weston Foundation. Logistical support was provided by Arctic National Wildlife Refuge, Barrow Arctic Science Consortium, BP Exploration (Alaska) Inc., Kinross Gold Corporation, Umiaq LLC, Selawik National Wildlife Refuge (USFWS), ConocoPhillips Alaska Inc., Cape Krusenstern National Monument (National Park Service) and Sirmilik National Park (Parks Canada). We thank local communities and landowners, including the Ukpeagvik Inupiat Corporation, the people of the Inuvialuit Settlement Region, Sitnasuak Native Corporation, the Kuukpik Corporation and the North Slope Borough for permitting us to conduct research on their lands.; Animal handling, marking and monitoring procedures were approved by Environment and Climate Change Canada, Government of Nunavut, Kansas State University, National Park Service, Ontario Ministry of Natural Resources and Forestry, University of Alaska Fairbanks, University of Moncton, US Fish & Wildlife Service and US Geological Survey. All applicable international, national and institutional guidelines for the care and use of animals were followed. We thank A. Tygart for assistance in compiling JAGS for use on the Beocat supercomputer at Kansas State University, D. Payer and S. Freeman for their work at Canning River, and H. Meltofte, P. Battley, B. Ross, J. Sutton, L. Martin and the Sandercock lab for comments on earlier drafts of the manuscript. We thank the many field assistants who were involved in data collection, especially field crew leaders K. Bennet, M. Burrell, J. Cunningham, E. D'Astous, S. Carvey, A. Doll, L. Pirie Dominix, K. Gold, A. Gottesman, K. Grond, P. Herzog, B. Hill, D. Hodgkinson, A. J. Johnson, D. Pavlik, M. Peck, L. Pollock, S. Sapora, B. Schwarz, F. Smith, H. M. Specht, M. VanderHeyden, B. M. Walker and B. Wilkinson. The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the US Fish and Wildlife Service. Any use of trade names is for descriptive purposes only and does not imply endorsement by the US Government. Public domain – authored by a U.S. government employee

Marking wild birds is an integral part of many field studies. However, if marks affect the vital rates or behavior of marked individuals, any conclusions reached by a study might be biased relative to the general population. Leg bands have rarely been found to have negative effects on birds and are frequently used to mark individuals. Leg flags, which are larger, heavier, and might produce more drag than bands, are commonly used on shorebirds and can help improve resighting rates. However, no one to date has assessed the possible effects of leg flags on the demographic performance of shorebirds. At seven sites in Arctic Alaska and western Canada, we marked individuals and monitored nest survival of four species of Arctic-breeding shorebirds, including Semipalmated Sandpipers (Calidris pusilla), Western Sandpipers (C. mauri), Red-necked Phalaropes (Phalarope lobatus), and Red Phalaropes (P. fielicarius). We used a daily nest survival model in a Bayesian framework to test for effects of leg flags, relative to birds with only bands, on daily survival rates of 1952 nests. We found no evidence of a difference in nest survival between birds with flags and those with only bands. Our results suggest, therefore, that leg flags have little effect on the nest success of Arctic-breeding sandpipers and phalaropes. Additional studies are needed, however, to evaluate the possible effects of flags on shorebirds that use other habitats and on survival rates of adults and chicks. National Fish and Wildlife Foundation [2010-0061-015, 2011-0032-014, 0801.12.032731, 0801.13.041129]; Neotropical Migratory Bird Conservation Act of the U.S. Fish and Wildlife Service [F11AP01040, F12AP00734, F13APO535, 4073, 4102]; Alaska Department of Fish and Game; State Wildlife Grant [T-16]; Arctic National Wildlife Refuge; Bureau of Land Management; Centre for Wildlife Ecology at Simon Fraser University; Environment and Climate Change Canada; Indigenous and Northern Affairs Canada; Kansas State University; Kresge Foundation; Liz Claiborne/Art Ortenberg Foundation; Manomet Center for Conservation Sciences; National Park Service; Murie Science and Learning Center Research Fellowship Program; National Science Foundation (Office of Polar Programs)National Science Foundation (NSF) [ARC-1023396]; National Science Foundation (Doctoral Dissertation Improvement Grant)National Science Foundation (NSF) [1501479]; Natural Resources Canada (Polar Continental Shelf Program); Natural Sciences and Engineering Research Council of Canada (Strategic Grant - Discovery Grants) [357054]; Northern Scientific Training Program (Canadian Polar Commission); U.S. Fish and Wildlife Service (Migratory Bird Management Division, Survey, Monitoring and Assessment Program); U.S. Fish and Wildlife Service (Alaska National Wildlife Refuge System's Challenge Cost Share Program); U.S. Fish and Wildlife Service (Avian Influenza Health and Influenza programs); U.S. Geological Survey (Changing Arctic Ecosystem Initiative, Wildlife Program of the USGS Ecosystem Mission Area); University of Colorado Denver; University of Alaska Fairbanks; University of Missouri Columbia Major support for the infrastructure of the Arctic Shorebird Demographics Network was provided by the Arctic Landscape Conservation Cooperative, National Fish and Wildlife Foundation (grants 2010-0061-015, 2011-0032-014, 0801.12.032731, and 0801.13.041129), and Neotropical Migratory Bird Conservation Act of the U.S. Fish and Wildlife Service (grants F11AP01040, F12AP00734, F13APO535, 4073, and 4102). Additional funding for individual sites was provided by Alaska Department of Fish and Game (including State Wildlife Grant T-16), Arctic National Wildlife Refuge, Bureau of Land Management, Centre for Wildlife Ecology at Simon Fraser University, Environment and Climate Change Canada, Indigenous and Northern Affairs Canada, Kansas State University, Kresge Foundation, Liz Claiborne/Art Ortenberg Foundation, Manomet Center for Conservation Sciences, National Park Service (including Murie Science and Learning Center Research Fellowship Program), National Science Foundation (Office of Polar Programs grant ARC-1023396 and Doctoral Dissertation Improvement Grant 1501479), Natural Resources Canada (Polar Continental Shelf Program), Natural Sciences and Engineering Research Council of Canada (Strategic Grant - 357054, Discovery Grants), Northern Scientific Training Program (Canadian Polar Commission), U.S. Fish and Wildlife Service (Migratory Bird Management Division, Survey, Monitoring and Assessment Program, Alaska National Wildlife Refuge System's Challenge Cost Share Program, and Avian Influenza Health and Influenza programs), U.S. Geological Survey (Changing Arctic Ecosystem Initiative, Wildlife Program of the USGS Ecosystem Mission Area), University of Colorado Denver, University of Alaska Fairbanks, and University of Missouri Columbia. We thank local communities and landowners, including the people of the Inuvialuit Settlement Region, North Slope Borough, Ukpeagvik Inupiat Corporation, and Sitnasuak Native Corporation for permitting us to conduct research on their lands. Logistical support was provided by Arctic National Wildlife Refuge (U.S. Fish and Wildlife Service), Barrow Arctic Science Consortium, Cape Krusenstern National Monument (National Park Service), ConocoPhillips Alaska, Inc., Sisualik National Wildlife Refuge (U.S. Fish and Wildlife Service), and Umiaq, LLC. We thank the many field assistants who helped on this project throughout the years, including S. Carvey, T. Donnelly, A. Gottesman, D. Pavlik, and B. Wilkinson for their key roles in field work at the Colville River Delta, and D. Payer for his key role in implementing and overseeing field work at Canning River Delta. J. Lamb, L. Rosen, and B. Ross provided comments on an early draft of the manuscript. Animal handling, marking, and monitoring procedures were approved by animal care and use committees and permitting agencies at Environment and Climate Change Canada, Kansas State University, National Park Service, University of Alaska Fairbanks, U.S. Fish and Wildlife Service, and U.S. Geological Survey - Alaska Science Center. The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service. Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Public domain – authored by a U.S. government employee

The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment1,2,3,4. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions1,5, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators6,7,8,9,10. Individuals can temporally segregate their daily activities (for example, prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (for example, group foraging, communal defence, pairs reproducing or caring for offspring)6,7,8,9,11. The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood5,6,7,9. Here we investigate these rhythms in the context of biparental care, a particularly sensitive phase of social synchronization12 where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within- and between-species diversity in incubation rhythms. Between species, the median length of one parent’s incubation bout varied from 1–19 h, whereas period length—the time in which a parent’s probability to incubate cycles once between its highest and lowest value—varied from 6–43 h. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or who actively protect their nest against predators. Rhythms entrainable to the 24-h light–dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity5,6,7,9. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms., The study was supported by the Max Planck Society (to B.K.). M.B. is a PhD student in the International Max Planck Research School for Organismal Biology.

Background Geolocators are useful for tracking movements of long-distance migrants, but potential negative effects on birds have not been well studied. We tested for effects of geolocators (0.8–2.0 g total, representing 0.1–3.9 % of mean body mass) on 16 species of migratory shorebirds, including five species with 2–4 subspecies each for a total of 23 study taxa. Study species spanned a range of body sizes (26–1091 g) and eight genera, and were tagged at 23 breeding and eight nonbreeding sites. We compared breeding performance and return rates of birds with geolocators to control groups while controlling for potential confounding variables. Results We detected negative effects of tags for three small-bodied species. Geolocators reduced annual return rates for two of 23 taxa: by 63 % for semipalmated sandpipers and by 43 % for the arcticola subspecies of dunlin. High resighting effort for geolocator birds could have masked additional negative effects. Geolocators were more likely to negatively affect return rates if the total mass of geolocators and color markers was 2.5–5.8 % of body mass than if tags were 0.3–2.3 % of body mass. Carrying a geolocator reduced nest success by 42 % for semipalmated sandpipers and tripled the probability of partial clutch failure in semipalmated and western sandpipers. Geolocators mounted perpendicular to the leg on a flag had stronger negative effects on nest success than geolocators mounted parallel to the leg on a band. However, parallel-band geolocators were more likely to reduce return rates and cause injuries to the leg. No effects of geolocators were found on breeding movements or changes in body mass. Among-site variation in geolocator effect size was high, suggesting that local factors were important. Conclusions Negative effects of geolocators occurred only for three of the smallest species in our dataset, but were substantial when present. Future studies could mitigate impacts of tags by reducing protruding parts and minimizing use of additional markers. Investigators could maximize recovery of tags by strategically deploying geolocators on males, previously marked individuals, and successful breeders, though targeting subsets of a population could bias the resulting migratory movement data in some species. Electronic supplementary material The online version of this article (doi:10.1186/s40462-016-0077-6) contains supplementary material, which is available to authorized users.

Seasonal declines in breeding performance are widespread in wild animals, resulting from temporal changes in environmental conditions or from individual variation. Seasonal declines might drive selection for early breeding, with implications for other stages of the annual cycle. Alternatively, selection on the phenology of nonbreeding stages could constrain timing of the breeding season and lead to seasonal changes in reproductive performance. We studied 25 taxa of migratory shorebirds (including five subspecies) at 16 arctic sites in Russia, Alaska, and Canada. We investigated seasonal changes in four reproductive traits, and developed a novel Bayesian risk-partitioning model of daily nest survival to examine seasonal trends in two causes of nest failure. We found strong seasonal declines in reproductive traits for a subset of species. The probability of laying a full four-egg clutch declined by 8–78% in 12 of 25 taxa tested, daily nest survival rates declined by 1–12% in eight of 22 taxa, incubation duration declined by 2.0–2.5% in two of seven taxa, and mean egg volume declined by 5% in one of 15 taxa. Temporal changes were not fully explained by individual variation. Across all species, the proportion of failed nests that were depredated declined over the season from 0.98 to 0.60, while the proportion abandoned increased from 0.01 to 0.35 and drove the seasonal declines in nest survival. An increase in abandonment of late nests is consistent with a life-history tradeoff whereby either adult mortality increased or adults deserted the breeding attempt to maximize adult survival. In turn, seasonal declines in clutch size and incubation duration might be adaptive to hasten hatching of later nests. In other species of shorebirds, we found no seasonal patterns in breeding performance, suggesting that some species are not subject to selective pressure for early breeding. This article is protected by copyright. All rights reserved.