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Most birds incubate their eggs to allow embryo development. This behaviour limits the ability of adults to perform other activities. Hence, incubating adults trade-off incubation and nest protection with foraging to meet their own needs. Parents can either cooperate to sustain this trade-off or incubate alone. The main cause of reproductive failure at this reproductive stage is predation and adults reduce this risk by keeping the nest location secret. Arctic sandpipers are interesting biological models to investigate parental care evolution as they may use several parental care strategies. The three main incubation strategies include both parents sharing incubation duties (?biparental?), one parent incubating alone (?uniparental?), or a flexible strategy with both uniparental and biparental incubation within a population (?mixed?). By monitoring the incubation behaviour in 714 nests of seven sandpiper species across 12 arctic sites, we studied the relationship between incubation strategy and nest predation. First, we described how the frequency of incubation recesses (NR), their mean duration (MDR), and the daily total duration of recesses (TDR) vary among strategies. Then, we examined how the relationship between the daily predation rate and these components of incubation behaviour varies across strategies using two complementary survival analysis. For uniparental and biparental species, the daily predation rate increased with the daily total duration of recesses and with the mean duration of recesses. In contrast, daily predation rate increased with the daily number of recesses for biparental species only. These patterns may be attributed to two independent mechanisms: cryptic incubating adults are more difficult to locate than unattended nests and adults departing the nest or feeding close to the nest can draw predators' attention. Our results demonstrate that incubation behaviour as mediated by incubation strategy has important consequences for sandpipers? reproductive success. This article is protected by copyright. All rights reserved.

Most birds incubate their eggs, which requires time and energy at the expense of other activities. Birds generally have two incubation strategies: biparental where both mates cooperate in incubating eggs, and uniparental where a single parent incubates. In harsh and unpredictable environments, incubation is challenging due to high energetic demands and variable resource availability. We studied the relationships between the incubation behaviour of sandpipers (genus Calidris) and two environmental variables: temperature and a proxy of primary productivity (i.e. NDVI). We investigated how these relationships vary between incubation strategies and across species among strategies. We also studied how the relationship between current temperature and incubation behaviour varies with previous day's temperature. We monitored the incubation behaviour of nine sandpiper species using thermologgers at 15 arctic sites between 2016 and 2019. We also used thermologgers to record the ground surface temperature at conspecific nest sites and extracted NDVI values from a remote sensing product. We found no relationship between either environmental variables and biparental incubation behaviour. Conversely, as ground-surface temperature increased, uniparental species decreased total duration of recesses (TDR) and mean duration of recesses (MDR), but increased number of recesses (NR). Moreover, small species showed stronger relationships with ground-surface temperature than large species. When all uniparental species were combined, an increase in NDVI was correlated with higher mean duration, total duration and number of recesses, but relationships varied widely across species. Finally, some uniparental species showed a lag effect with a higher nest attentiveness after a warm day while more recesses occurred after a cold day than was predicted based on current temperatures. We demonstrate the complex interplay between shorebird incubation strategies, incubation behaviour, and environmental conditions. Understanding how species respond to changes in their environment during incubation helps predict their future reproductive success.

While increases in overall temperatures are widely reported in the Arctic, large inter-annual variation in spring weather, with extreme early and late conditions, is also occurring. Using data collected from three sites in Arctic Alaska, we explored how shorebird breeding density, nest initiation, nest synchrony, nest survival, and phenological mismatch varied between two exceptionally early (2015 and 2016) and late (2017 and 2018) springs. We assessed these differences in the context of long-term data from each site and whether species exhibited conservative or opportunistic reproductive strategies. Conservative shorebirds typically display nest-site fidelity and territoriality, consistent population densities, relatively even individual spacing, and monogamous mating systems with bi-parental incubation. In contrast, opportunistic shorebirds display the opposite traits, and a polygamous mating system with uniparental incubation. In this study, we evaluated 2,239 nests from 13 shorebird species, 2015–2018, and found that shorebirds of both strategies bred earlier and in higher numbers in early, warm springs relative to historic levels (based on 3,789 nests, 2005–2014); opposite trends were observed in late springs. In early springs, nests were initiated less synchronously than in late springs. Nest survival was unrelated to spring type, but was greater in earlier laid nests overall. Invertebrate food resources emerged earlier in early springs, resulting in a greater temporal asynchrony between invertebrate emergence and chick hatching in early than late springs. However, invertebrate abundance was quite variable among sites and years regardless of spring type. Overall, our results were generally consistent with predicted relationships between spring conditions and reproductive parameters. However, we detected differences among sites that could not be explained by other ecological factors (e.g., predators or alternative prey). Differences in shorebird community composition and other subtler methodological/ecological differences among sites highlight the difficulty of understanding the complex nature of these ecological systems and the importance of evaluating questions at multiple sites across multiple years. Our study demonstrates that shorebirds exhibit a high degree of behavioral flexibility in response to variable Arctic conditions, but whether this flexibility is enough to allow them to optimally track changing environmental conditions or if evolutionary adjustments will be necessary is unknown.

Ecological “big data” Human activities are rapidly altering the natural world. Nowhere is this more evident, perhaps, than in the Arctic, yet this region remains one of the most remote and difficult to study. Researchers have increasingly relied on animal tracking data in these regions to understand individual species' responses, but if we want to understand larger-scale change, we need to integrate our understanding across species. Davidson et al. introduce an open-source data archive that currently hosts more than 15 million location data points across 96 species and use it to show distinct climate change responses across species. Such ecological “big data” can lead to a wider understanding of change. Science , this issue p. 712

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.

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

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.