Miniaturized light-level geolocators provide novel insight into the migration ecology of an endangered songbird

Understanding songbird movements throughout their annual cycles is critical to inform conservation planning decisions and management priorities for migratory species. From 2017 to 2020, we attached miniaturized light-level geolocators to 309 male golden-cheeked warblers (Setophaga chrysoparia; hereafter warbler) at five study sites located across the species’ breeding range in Texas. From 2018 to 2021, we recovered data from 61 geolocators and used these data to determine the locations and timing of warbler movements during their non-breeding seasons and to quantify migratory connectivity and migration networks for the species. Mean duration of fall migration (37 d ±19 d) was longer than spring migration (27 d ±14 d), and, on average, second-year warblers initiated fall migration 10 d ±13 d earlier than after-second-year warblers. Migration initiation dates during spring, as well as duration and distance of fall and spring migrations, were similar for both age classes. Overall, 80% of warblers migrated along the Sierra Madre Oriental and Mexico’s Gulf coast between their breeding grounds in Texas and wintering grounds in southern Mexico and Central America during fall and spring; 20% migrated across or eastward around the Gulf of Mexico, primarily in fall. Overall, stopover duration varied along the warbler’s migration route (range = 3–61 d), with the longest stopovers in Texas and along the coast of Tamaulipas and Veracruz in Mexico. The highest percentages of stationary overwintering locations occurred in Chiapas, Mexico (27%), Guatemala (25%), and Honduras (17%), and many warblers used more than one location during winter. Some warblers used areas outside the predicted winter range; one extralimital location was confirmed during field-based surveys in Oaxaca, Mexico. Our results suggested that warblers exhibit weak migratory connectivity and likely disperse widely across the winter range. Given the narrow migration pathway used by most warblers and confined winter range in montane forests, continued and increased conservation along the warbler’s migration route and on the wintering grounds could help ensure population persistence and simultaneously protect co-occurring species.