Using Light-Level Geolocator Technology to Examine Movement Ecology for an Endangered Songbird, the Golden-Cheeked Warbler
Abstract
Sixty percent of neotropical migratory songbirds have experienced population declines over the last century and there is growing evidence that events during non-breeding periods contribute to their declines. Unfortunately, we lack data to describe habitat associations and movements during non-breeding periods for most species. Such information is necessary to develop and implement effective conservation strategies for migratory songbirds, but can be difficult to obtain given the size of most tracking devices. One exception is the miniaturized light-level geolocator, which records light intensity data that can be used to estimate locations once the device is retrieved. The golden-cheeked warbler (Setophaga chrysoparia; hereafter warbler) is a very small (<12 g) endangered migratory songbird that breeds in central Texas and overwinters in southern Mexico and Central America. I deployed geolocators on male warblers at five study sites in Texas to examine their movements during non-breeding periods and to quantify migratory connectivity for the species. I simultaneously quantified the potential impacts of geolocators on aspects of warbler survival and reproductive behavior at two of my study sites. Most warblers quickly resumed normal activities after geolocator deployment, showed no visible signs of injuries, and had similar body mass before and after carrying geolocators. I found few differences in pairing success, fledging success, and return rates, for warblers with and without geolocators, and the differences I observed were driven by age. I found that most warblers moved a considerable distance from their breeding site to another location outside their breeding range before initiating fall migration. In addition, fall migration was longer than spring, and second year warblers initiated fall migration earlier than after second year warblers. Eighty percent of warblers migrated over land and 20% migrated over the Gulf. Stopover duration varied along the warbler’s migration route. The highest concentrations of overwintering locations occurred in three areas, and many warblers used >1 winter location. Warblers exhibited weak migratory connectivity, however, given their relatively narrow migration pathway and small winter range, continued and increased conservation in non-breeding areas could help ensure population persistence and protect co-occurring species.
Description
Keywords
light-level geolocator, golden-cheeked warbler, migratory connectivity