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Global climate change has altered the timing of seasonal events (i.e., phenology) for a diverse range of biota. Within and among species, however, the degree to which alterations in phenology match climate variability differ substantially. To better understand factors driving these differences, we evaluated variation in timing of nesting of eight Arctic‐breeding shorebird species at 18 sites over a 23‐year period. We used the Normalized Difference Vegetation Index as a proxy to determine the start of spring (SOS) growing season and quantified relationships between SOS and nest initiation dates as a measure of phenological responsiveness. Among species, we tested four life history traits (migration distance, seasonal timing of breeding, female body mass, expected female reproductive effort) as species‐level predictors of responsiveness. For one species (Semipalmated Sandpiper), we also evaluated whether responsiveness varied across sites. Although no species in our study completely tracked annual variation in SOS, phenological responses were strongest for Western Sandpipers, Pectoral Sandpipers, and Red Phalaropes. Migration distance was the strongest additional predictor of responsiveness, with longer‐distance migrant species generally tracking variation in SOS more closely than species that migrate shorter distances. Semipalmated Sandpipers are a widely distributed species, but adjustments in timing of nesting relative to variability in SOS did not vary across sites, suggesting that different breeding populations of this species were equally responsive to climate cues despite differing migration strategies. Our results unexpectedly show that long‐distance migrants are more sensitive to local environmental conditions, which may help them to adapt to ongoing changes in climate. [ABSTRACT FROM AUTHOR]

We quantified variation in winter survival of Surf Scoters (Melanitta perspicillata (L., 1758)) across nearly 30° of latitude on the Pacific coast of North America to evaluate potential effects on winter distributions, including observed differential distributions of age and sex classes. We monitored fates of 297 radio-marked Surf Scoters at three study sites: (1) near the northern periphery of their wintering range in southeast Alaska, USA, (2) the range core in British Columbia, Canada, and (3) the southern periphery in Baja California, Mexico. We detected 34 mortalities and determined that survival averaged lower at the range peripheries than in the range core, was lower during mid-winter than during late winter at all sites, and was positively correlated with body mass within locations. Although neither age nor sex class had direct effects, mass effects led to differential survival patterns among classes. When simultaneously incorporating these interacting influences, adult males of mean mass for their location had highest survival at the northern range periphery in Alaska, whereas adult females and juveniles had higher survival at the range core and the southern periphery. Our observations help to explain patterns of differential migration and distribution reported for this species and highlight seasonal periods (mid-winter) and locations (range peripheries) of elevated levels of mortality for demographically important age-sex classes (adult females). Key words: demography, distribution, Melanitta perspicillata, sea duck, Surf Scoter. Nous avons quantifie les variations de la survie hivernale des macreuses a front blanc (Melanitta perspicillata (L., 1758)) sur 30 de latitude le long de la cote pacifique de l'Amerique du Nord afin d'en evaluer les effets potentiels sur la repartition hivernale, dont differentes repartitions observees selon les classes d'age et de sexe. Nous avons surveille le destin de 297 macreuses munies de radioemetteurs dans les trois sites d'etude suivants : (1) pres de la bordure nord de leur aire d'hivernage dans le sud-estde l'Alaska(Etats-Unis), (2) aucreurde leur aire de repartition en Colombie-Britannique (Canada) et (3) a la bordure meridionale de leur aire de repartition, en Basse-Californie (Mexique). Nous avons releve 34 cas de mortalite et determine que la survie moyenne etait plus faible en bordure de l'aire de repartition qu'en son centre, qu'elle etait plus faible au milieu de l'hiver qu'a la fin de l'hiver dans tous les sites, et qu'elle etait possiblement correlee a la masse du corps a l'interieur d'un meme site. Si ni la classe d'age, ni la classe de sexe n'avaient d'effet direct, des effets de la masse entrainaient differents motifs de survie au sein des classes. Quand ces influences interactives etaient incluses simultanement, les males adultes de masse moyenne pour leur emplacement presentaient le taux de survie le plus eleve a la bordure nord de l'aire de repartition en Alaska, alors que les femelles adultes et les juveniles presentaient le plus grand taux de survie au centre de l'aire de repartition et a sa bordure meridionale. Nos observations aident a expliquer les motifs de migration et de repartition differentielles signales pour cette espece et font ressortir des periodes saisonnieres (le milieu de l'hiver) et des lieux (aux bordures de l'aire de repartition) de mortalite elevee pour des classes d'age et de sexe importantes sur le plan demographique (femelles adultes). [Traduit par la Redaction] Mots-cles: demographie, repartition, Melanitta perspicillata, canard marin, macreuse a front blanc., Introduction Understanding factors affecting animal distributions is a fundamental issue in ecology. Migratory animals often occur in a variety of habitats and conditions both among and within annual cycle stages. [...]