Responses of an Endangered Songbird to an Extreme Drought Event

Given natural variation in weather conditions and increased risk of drought associated with climate change, understanding how birds respond to fluctuations in precipitation is a necessary step toward development of more-effective, long-term management strategies for species of conservation concern. We compared behaviors and reproductive output of the federally endangered Vireo atricapilla (Black-capped Vireo, hereafter Vireo) during an extreme drought event and a year with moderate rainfall. During the drought, Vireos had lower pairing and territory success, delayed nest initiation, fewer re-nesting attempts, and lower nest-success. Brood parasitism by Molothrus ater (Brown-headed Cowbirds), which is one of the main threats to Vireo population persistence, was also greater during the drought year. Nest placement varied between years, with Vireos using the evergreen Juniperus asheii (Ashe Juniper) as a nest substrate more often when conditions were dry and the deciduous Diospyros texana (Texas Persimmon) under moderate conditions. Removal of Ashe Juniper and Brown-headed Cowbirds from Vireo habitat are common management practices used to support Vireo conservation efforts. Our results suggest that regional weather patterns should be considered when making decisions regarding Ashe Juniper removal. In addition, increased Brown-headed Cowbird removal may be warranted in dry areas during drought years.