Environmental and demographic mechanisms provide relative stability for a vulnerable island songbird in novel conditions

Understanding demographic and ecological mechanisms underlying population dynamics is a key goal in population ecology and critical for effective management in the face of climate change. Species may be well adapted to persist under normal ranges of environmental conditions, but increasingly novel environmental conditions may surpass the demographic buffering mechanisms in many populations. Small, isolated populations, such as those on islands, are expected to be especially vulnerable to declines caused by novel environmental conditions. We used an integrated population model to (1) examine ecological drivers of population growth and (2) assess global population trends of the Island Scrub-Jay ( Aphelocoma insularis ) from 2009-2019. Our results suggest that population size increased slightly over this interval despite declines during severe drought. We also found evidence that density dependence, precipitation, and food availability affected fecundity and the survival of non-breeding individuals. Breeder survival was relatively stable and had a weak effect on population growth as expected for long-lived species. Overall, our results provide an optimistic snapshot for this species by demonstrating resilience to contemporary drought, but also emphasize the species’ potential vulnerability due to its small population size.