UC Davis

Effects of climatic change are observed to be rapidly increasing, particularly in northern latitudes. Some of the results of climate change include increased climatic stochasticity, which results in high inter-annual variability in the timing of spring onset. Migratory species that rely on these northern climates may be impacted disproportionately by these changes because they utilize networks of diverse habitats over a large area that are experiencing different rates and effects of climate variability. However, short-distance migrants like the Common Goldeneye (Bucephala clangula) may be better able to track phenological changes due to similarities in climate conditions on wintering and breeding grounds. I used a long-term dataset (1997-2020) of Common Goldeneye nesting records from interior Alaska, near the northern extent of the species’ range, to examine the impacts of changing spring phenology on reproductive ecology. I used nesting initiation date as an indicator of breeding phenology and examined how nest initiation date varied over the 23-year study period. I then evaluated the influence of predictor variables related to spring conditions, winter conditions, female body condition, and known breeding experience on nest initiation date. Finally, I examined trends in female body condition during the study period and examined the relationship of body condition to winter conditions and known breeding experience. Across all analyses, my results indicated that nest initiation dates varied significantly with measures of spring phenology, wintering area conditions, body condition, and previous breeding. Model estimates indicate that the mean nest initiation date for this population is advancing at 0.71 days per year. Unexpectedly, poorer body condition was correlated with warmer winter conditions, which may result in future impacts on reproductive output as climate change advances. Model results also demonstrated high repeatability of individual females as a random effect, meaning that females may consistently respond to climatic conditions independently from other females, suggesting that female personality may influence phenological responses. Though goldeneyes appear to currently track the advancement of spring conditions, my results suggest that these migratory birds rely on multiple signals to determine timing of nesting, and uncertainty remains as to how these signals may interact to influence breeding phenology in the future.