Post-fledging survival, movement patterns, and habitat associations of Bendire's Thrashers (Toxostoma bendirei) in the Chihuahuan Desert

Abstract

Knowledge gaps about the basic demography of a species facing population declines impede conservation efforts. For many passerine species, the survival rate of the post-fledging stage is unknown but may directly contribute to population trajectories. Bendire’s Thrasher (Toxostoma bendirei) exhibits steep population declines in the southwestern United States, yet little is known about the basic breeding biology of this species. We examined juvenile Bendire’s Thrasher survival during the post-fledging period and movement patterns from the nest site. We attached transmitters to 25 nestlings and tracked 19 fledglings using radio-telemetry. Using the known fate survival method, we modeled fledgling weekly survival in relation to age, time, and body condition, as well as habitat characteristics recorded at tracking locations. The top ranked model indicated that weekly survival increased with age since fledging (β = 0.225, 95% CI: 0.109, 0.340), and survival was low (< 50%) during the first 10 days post-fledging. Predation pressure on fledglings was strong because they were not capable of flight for the first several days after leaving the nest. Distances moved from the nest increased with fledgling age, and in general, fledglings remained with family units (siblings and adults) on or near the breeding territory until the family unit dispersed. Further investigation into the post-fledging stage, in combination with other life cycle stages, will be critical for future conservation and population growth of Bendire’s Thrashers within the Chihuahuan Desert.