Juvenile and Adult Survival Estimates of American Kestrels Throughout the Full Annual Cycle in Eastern North America

Abstract

Measuring survival in a declining species provides the foundation for continued research, demographic modeling, and informed conservation strategies. Although American Kestrel (Falco sparverius) populations have continued to decline since the 1970s, little is known about their survival throughout the full annual cycle, making it difficult to identify factors responsible for these declines. We used radio telemetry to provide the first known-fate estimates of adult kestrel survival, and we present data across breeding stages, and between resident and migratory wintering individuals, in addition to separately modeling fledgling survival. Temporal and spatial stratification of study sites allowed for the investigation of different pressures and risks that may lead to variation in survival. We generated weekly survival estimates for 56 adult kestrels in Pennsylvania and Florida, and for 146 recently fledged kestrels at five study sites throughout northeastern North America from 2021 to 2023. Adult weekly survival varied by sex and season, with males in the nonbreeding season exhibiting the lowest values (0.9074). Overwinter survival at our Pennsylvania study site (0.9316) was lower than in Florida (0.9881), indicating potential survival costs to overwintering at these locations. Post-fledging juvenile weekly survival estimates varied among five study sites (0.9429 to 1.000) and were much higher than expected based on previous work and the presumed difficulty of surviving this vulnerable early life stage. This insight into where and when mortality occurs in this declining species provides key parameters for demographic modeling and refines potential targeted conservation planning.