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Seasonally abundant arthropods are a crucial food source for many migratory birds that breed in the Arctic. In cold environments, the growth and emergence of arthropods are particularly tied to temperature. Thus, the phenology of arthropods is anticipated to undergo a rapid change in response to a warming climate, potentially leading to a trophic mismatch between migratory insectivorous birds and their prey. Using data from 19 sites spanning a wide temperature gradient from the Subarctic to the High Arctic, we investigated the effects of temperature on the phenology and biomass of arthropods available to shorebirds during their short breeding season at high latitudes. We hypothesized that prolonged exposure to warmer summer temperatures would generate earlier peaks in arthropod biomass, as well as higher peak and seasonal biomass. Across the temperature gradient encompassed by our study sites (>10°C in average summer temperatures), we found a 3-day shift in average peak date for every increment of 80 cumulative thawing degree-days. Interestingly, we found a linear relationship between temperature and arthropod biomass only below temperature thresholds. Higher temperatures were associated with higher peak and seasonal biomass below 106 and 177 cumulative thawing degree-days, respectively, between June 5 and July 15. Beyond these thresholds, no relationship was observed between temperature and arthropod biomass. Our results suggest that prolonged exposure to elevated temperatures can positively influence prey availability for some arctic birds. This positive effect could, in part, stem from changes in arthropod assemblages and may reduce the risk of trophic mismatch.

Documentation of Carry-Over Effects (COEs), defined as effects resulting from events that occurred in a previous time period, has largely been observational and understanding of specific mechanisms underlying COEs is still lacking. To investigate this, we simulated an environmental perturbation during the spring migration of a long-lived bird species and looked at the subsequent effects on various breeding parameters. We captured female greater snow geese (Anser caerulescens atlanticus) on their spring staging sites and maintained individuals in captivity for up to four days before releasing them. We re-observed females 3000 km North, on their Arctic breeding grounds, to estimate their breeding propensity (i.e., probability of initiating a reproductive event for a given year), and measure their arrival date, laying date, clutch size, and nesting success. Only proxies of breeding propensity were affected by our manipulation, which decreased as the time spent in captivity increased. However, females were able to overcome the effects of captivity in two out of the three years of experimentation with normal or good environmental conditions at the breeding site. When facing the additional challenge of poor environmental conditions, many individuals manipulated during migration apparently curtailed their reproductive effort by skipping breeding. This experiment is the first to show that breeding propensity is an important parameter affected by COEs resulting from stressful events prior to reproduction in long-lived species., 1. La documentation des effets reportés (Carry-Over Effect en anglais, COE), phénomène défini comme étant un effet résultant d’un événement qui s’est produit à un moment antérieur, a été effectuée principalement par observation et la compréhension des mécanismes spécifiques sous-jacents aux COEs est toujours manquante. Pour investiguer ceci, nous avons simulé une perturbation environnementale durant la migration d’une espèce longévive et avons observé les effets subséquents sur différents paramètres de reproduction. 2. Nous avons capturé des femelles grande oie des neiges (Anser caerulescens atlanticus) sur leur halte migratoire printanière et avons maintenu des individus en captivité jusqu’à quatre jours avant de les relâcher. Nous avons réobservé ces femelles 3000 km au Nord, sur leur territoire de nidification arctique, pour déterminer leur propension à se reproduire (la probabilité d’initier un événement reproducteur pour une année donnée), leur date d’arrivée, leur date de ponte, leur taille de ponte et leur succès d’éclosion. 3. Seuls les proxys de la propension à se reproduire ont été affectés par notre manipulation, diminuant lorsque le temps passé en captivité augmentait. Cependant, les femelles étaient capables de compenser pour l’effet du temps passé en captivité lors de deux des trois années d’étude avec des conditions environnementales normales ou bonnes sur les sites de nidification. 4. Faisant face au défi additionnel des conditions environnementales défavorables sur les territoires de nidification, plusieurs individus manipulés durant la migration semblent avoir abrégé leurs efforts de nidification en sautant la reproduction. Cette expérience est la première à montrer que la propension à se reproduire est un paramètre important permettant de remédier aux COEs résultant d’un événement stressant avant la reproduction chez une espèce longévive.