Timing mismatches between nesting and peak prey availability impacts reproductive success in a migratory aerial insectivore.

With climate change, animals must adjust seasonal life cycle timing, but constraints may cause mismatches with key resources. Avian long-distance migrants exhibit flexibility in nest timing to local conditions after arrival in spring. However, it is unclear whether plasticity in egg-laying timing is sufficient to match peak prey availability or whether phenological mismatch affects reproductive success. Such mismatches have been invoked as a potential cause of population decline in avian aerial insectivores, but mechanisms have not been directly investigated. We investigated the alignment between nest timing and peak insect prey availability in a declining, migratory aerial insectivore (purple martin, Progne subis). We examined the extent to which birds aligned peak energetic demand during nesting with available insects and tested the hypothesis that misalignment between prey resources and peak energetic demand during nest provisioning limits fledging success. We examined alignment with overall insect abundance and specific insect groups preyed upon by martins. We found evidence of a phenological mismatch between peak prey availability and nest timing that impacted fledging success. Nests less aligned with the overall insect peak and Odonate peak fledged later. Similarly, a lower proportion of young fledged when later nesting stages were less aligned with Lepidopteran and Odonate peaks. When peak provisioning periods aligned less with Odonate peak, fewer young fledged overall. Our results demonstrate a strong fitness disadvantage when nests are mistimed with key prey availability. Future research should examine connections between phenological mismatch and current population declines in aerial insectivores.