Natural variation in migratory strategies across the range of the American Kestrel (Falco sparverius) creates a unique opportunity for comparative research of annual cycles. However, it can be logistically and technically challenging to track such a small but highly mobile species. We tagged American Kestrels with light-level geolocators or satellite transmitters with the aim of estimating migration timing and connectivity, and we monitored a subset of satellite-tagged individuals during the breeding season to assess transmitter function and wear. We recovered geolocators from six of 49 (12%) tagged individuals. One geolocator-tagged individual migrated approximately 1235 km from its Idaho breeding grounds to New Mexico near the Arizona border for the winter and returned to Idaho the following spring. The other five recaptured individuals remained near (< 200 km) the breeding grounds year-round. The low reliability of recovery and low precision of locations suggested major limitations of using geolocators to track this species. Most satellite transmitters (18 of 22, 82%) failed prior to migration, but one satellite-tagged individual migrated approximately 5945 km from Canada to Nicaragua, and three others transmitted ≥1 location during migration. Transmitters stopped functioning while on live individuals despite showing no visible damage and maintaining adequate battery levels. These results suggest further testing and development are needed before these recently developed tags are deployed again on American Kestrels. Both individuals with complete migration tracks showed evidence of short distance (250–350 km) post-breeding movements to southern stopover sites where they stayed 1–3 mo before migrating onward. Although sample sizes were small, migration patterns were consistent with latitudinal leap-frog patterns described in previous studies and revealed an interesting pattern of a prolonged post-breeding stopover before longer migration. Further, the migration track from Canada to Nicaragua represents the longest recorded migration path for this species.
This document was originally published in Journal of Raptor Research by Raptor Research Foundation. Copyright restrictions may apply. https://doi.org/10.3356/JRR-22-05
Hunt, Anjolene R.; Watson, Jesse L.; Winiarski, Jason M.; Porter, Ron R.; and Heath, Julie A.. (2023). "American Kestrel Migration: Insights and Challenges from Tracking Individuals Across the Annual Cycle". Journal of Raptor Research, 57(2), 164-175. https://doi.org/10.3356/JRR-22-05