The realized environmental niche varies by biological level in a broadly distributed migratory waterbird, Pelecanus erythrorhynchos (American White Pelican)

Abstract Quantifying individual-level variation of environmental niches can provide insight into potential species-level response to environmental change. For migratory species, wide individual environmental niche breadth (the range of environments within a niche) and high variability (the degree of change in environments encompassed within a niche over time) between seasons suggest a species may be relatively resilient to effects of environmental change. Yet, seasonal niche overlap and variability of both individuals and populations have been quantified for few avian species, despite the importance of understanding individual contribution to species-level responses. Pelecanus erythrorhynchos (American White Pelican; hereafter, “pelican”) is a migratory waterbird with a broad distribution across North America. Pelicans in the Pacific Flyway have shifted their breeding range a median 114 km northward over the past 50 years, but the causes of this shift and an understanding of how populations might respond to future environmental change are lacking. We quantified the overlap and variability of this species’ realized environmental niche at population- and individual-levels using 4 climate-related variables and a multi-year GPS telemetry dataset collected from 13 individuals in the Pacific Flyway. When all environmental variables were considered together, the population showed only moderate overlap between the breeding and nonbreeding range niches (Schoener’s D = 0.20). Most individuals did not track their niche seasonally, suggesting that the population may be relatively resilient to environmental change. However, when considering each environmental variable alone, the population tracked only minimum monthly temperature, suggesting that increasing temperatures play an important role in driving northward breeding range shifts through the expansion of available breeding habitat and physiologically tolerable conditions, while the established effects of drought and water limitations impact southern portions of the breeding range. Our research underscores the importance of examining both individual- and population-level niche overlap and variability to understand resilience to environmental change.