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The ecological consequences of climate change have been recognized in numerous species, with perhaps phenology being the most well‐documented change. Phenological changes may have negative consequences when organisms within different trophic levels respond to environmental changes at different rates, potentially leading to phenological mismatches between predators and their prey. This may be especially apparent in the Arctic, which has been affected more by climate change than other regions, resulting in earlier, warmer, and longer summers. During a 7‐year study near Utqiaġvik (formerly Barrow), Alaska, we estimated phenological mismatch in relation to food availability and chick growth in a community of Arctic‐breeding shorebirds experiencing advancement of environmental conditions (i.e., snowmelt). Our results indicate that Arctic‐breeding shorebirds have experienced increased phenological mismatch with earlier snowmelt conditions. However, the degree of phenological mismatch was not a good predictor of food availability, as weather conditions after snowmelt made invertebrate availability highly unpredictable. As a result, the food available to shorebird chicks that were 2–10 days old was highly variable among years (ranging from 6.2 to 28.8 mg trap−1 day−1 among years in eight species), and was often inadequate for average growth (only 20%–54% of Dunlin and Pectoral Sandpiper broods on average had adequate food across a 4‐year period). Although weather conditions vary among years, shorebirds that nested earlier in relation to snowmelt generally had more food available during brood rearing, and thus, greater chick growth rates. Despite the strong selective pressure to nest early, advancement of nesting is likely limited by the amount of plasticity in the start and progression of migration. Therefore, long‐term climatic changes resulting in earlier snowmelt have the potential to greatly affect shorebird populations, especially if shorebirds are unable to advance nest initiation sufficiently to keep pace with seasonal advancement of their invertebrate prey.

Detailed information on the nutrition of free-ranging mammals contributes to the understanding of life history requirements, yet is often quite limited temporally for most species. Reliable dietary inferences can be made by analyzing the stable carbon (C) and nitrogen (N) isotopic values (δ13C and δ15N) of some consumer tissues; exactly which tissue is utilized dictates the inferential scope. Steller sea lion (SSL) vibrissae are grown continuously without shedding and thus provide a continuous multi-year record of dietary consumption. We applied a novel kernel density approach to compare the δ13C and δ15N values along the length of SSL vibrissae with δ13C and δ15N distributions of potential prey species. This resulted in time-series of proportion estimates of dietary consumption for individual SSL. Substantial overlap in δ13C and δ15N distributions for prey species prevented a discrete species-scale assessment of SSL diets; however, a post hoc correlational analysis of diet proportion estimates revealed grouping by trophic level. Our findings suggest that adult female SSL diets in the western and central Aleutian Islands shift significantly according to season: diets contain a higher proportion of lower trophic level species (Pacific Ocean perch, northern rockfish, Atka mackerel and walleye pollock) in the summer, whereas in the winter SSL consume a much more diverse diet which includes a greater proportion of higher trophic level species (arrowtooth flounder, Kamchatka flounder, darkfin sculpin, Pacific cod, Pacific octopus, rock sole, snailfish, and yellow Irish lord).

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.

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 use of stable isotopes in animal ecology depends on accurate descriptions of isotope dynamics within individuals. The prevailing assumption that laboratory-derived isotopic parameters apply to free-living animals is largely untested. We used stable carbon isotopes (δ13C) in whole blood from migratory Dunlin (Calidris alpina arcticola) to estimate an in situ turnover rate and individual diet-switch dates. Our in situ results indicated that turnover rates were higher in free-living birds, in comparison to the results of an experimental study on captive Dunlin and estimates derived from a theoretical allometric model. Diet-switch dates from all 3 methods were then used to estimate arrival dates to the Arctic; arrival dates calculated with the in situ turnover rate were later than those with the other turnover-rate estimates, substantially so in some cases. These later arrival dates matched dates when local snow conditions would have allowed Dunlin to settle, and agreed with anticipated arrival d...

© Inter-Research 2015. Multiple factors, including limitation in food resources, have been proposed as possible causes for the lack of recovery of the endangered western segment of the Steller sea lion population in the United States. Because maternal body condition has important consequences on fetal development and neonatal survival, the diets of pregnant females may be particularly important in regulating population sizes. We used the stable carbon and nitrogen isotope values of vibrissae from Steller sea lion pups as an indirect indicator of maternal diets during gestation. Combining these data with isotope data from potential prey species in a Bayesian mixing model, we generated proportional estimates of dietary consumption for key prey. Our analysis indicated that females in the most westerly metapopulations relied heavily on Atka mackerel and squid, whereas females inhabiting the Gulf of Alaska region had a fairly mixed diet, and the metapopulation of Southeast Alaska showed a strong reliance on forage fish. These results are similar to previous data from scat collections; however, they indicate a possible under-representation of softbodied prey (squid) or prey with fragile skeletons (forage fish) from analyses of data from scats. This study supports the utility of stable isotope modeling in predicting diet composition in gestating adult female Steller sea lions during winter, using pup vibrissae.