ESR prepress abstract   -  DOI: https://doi.org/10.3354/esr01344

ABSTRACT: Migration is an essential life stage in many species, but is little known in some groups like storm-petrels. Considering that storm-petrels reside in non-breeding areas for over half of their lifespan, identifying those areas is a priority for conservation efforts. Townsend’s Hydrobates socorroensis and Ainley’s storm-petrels (H. cheimnomnestes) are 2 threatened sister species breeding allochronically in Guadalupe Island (Mexican Pacific), for which migratory patterns are unknown. In this article, we describe the non-breeding areas of these 2 species, assess artificial light events by the geolocators, and describe their daily activity patterns. We deployed geolocators from 2021 to 2023 and modelled their migratory routes using SGAT. We successfully tracked 7 Townsend’s and 4 Ainley’s storm-petrels over their non-breeding period. In the case of Townsend’s, birds travelled to the south of the Baja California Peninsula, but not in the case of Ainley’s storm-petrel, in which birds migrated toward Hawaii. Townsend’s spent most of the time in Mexican waters, while Ainley’s storm-petrel spent most time in high seas. Townsend's core areas have 16.1% of its core areas protected, whereas Ainley's storm-petrel has only 0.7% protected, and 0.8% of those areas recognized as KBAs. Further, our findings indicate that both species are mainly nocturnal, making them highly susceptible to the impacts of light pollution, and we detected 6 artificial light events. Our findings also support the hypothesis that divergence in the migration between allochronic populations could be a crucial factor in sympatric speciation, which seems likely in seasonal environments like the northern Pacific.