Patterns of migratory connectivity in Vaux’s Swifts at a northern migratory roost: a multi- isotope approach

The strength of migratory connectivity between breeding, stopover, and wintering areas can have important implications for population dynamics, evolutionary processes, and conservation. For example, patterns of migratory connectivity may influence the vulnerability of species and populations to stochastic events. For many migratory songbirds, however, we are only just beginning to understand patterns of migratory connectivity. Here, we investigate the potential strength of migratory connectivity within a population of Vaux’s Swifts (Chaetura vauxii). Vaux’s Swifts, like many aerial insectivores, are currently experiencing population declines, and a mass mortality event at a spring migratory roost on Vancouver Island, British Columbia, Canada, resulted in the death of over 1,000 individuals, representing some 2% of the British Columbia population. From these individuals, we examined variation in three stable-isotopes (δ2H, δ13C, and δ15N) from claw samples in order to determine whether spring migrants showed inherent isotopic similarity of the habitats they used on their Mexican and Central American wintering grounds. Our results indicated the presence of two to three broad isotopic clusters, suggesting that Vaux’s Swifts migrating through Vancouver Island most likely originated from two or three over-wintering locales or habitat types. We found no evidence of sex- or morphology-based segregation, suggesting that these different groups likely share a similar overwintering ecology and thus may be equally vulnerable to stochastic events or habitat loss on the wintering grounds. Our results highlight the need for more studies on the non-breeding season ecology and migratory connectivity of this species.