Long-distance dispersal patterns in the Cerulean Warbler: a case study from Indiana

Dispersal, defined as movement an individual makes from one breeding population to another, is a process that strongly influences the population dynamics of many animal species. Although dispersal across longer distances is believed to be a relatively uncommon phenomenon for most bird species, movements between populations drive numerous ecological processes, and understanding rates and directions of dispersal are especially important when considering species of conservation concern. The Cerulean Warbler (Setophaga cerulea) is a Nearctic-Neotropical songbird that breeds in mature forests of eastern and central North America and has experienced significant declines in recent decades largely due to habitat loss on the breeding grounds. Previous research suggests that Cerulean Warblers exhibit high rates of long-distance dispersal and that populations may be shifting away from the peripheral edges of its breeding range. The potential impacts of dispersal on reproductive success, however, remain unknown for this species. In this study, we used a long-term dataset (2013-2021) to investigate dispersal rates, age-related differences in dispersal, and effects of immigration on nest success in a population of Cerulean Warblers in south-central Indiana. To categorize birds as either immigrants or residents, we analyzed naturally occurring stable-hydrogen isotopes in tail feathers grown on the breeding grounds. We found an overall high rate (26.5%) of long-distance dispersal in this population, and the majority of these immigrants appeared to have originated from latitudes south of our study site. Additionally, our findings suggest that dispersal rates of juveniles and adults are very similar in this population, and that immigration appears to have no effect on reproductive success. This study contributes to our limited knowledge of the Cerulean Warblers' full annual cycle ecology, and our reported high dispersal rate and lack of effect of immigration on nest success have encouraging implications for the conservation of this declining species.