Post-fledging survival, movements, and habitat associations of Gray Vireos in New Mexico

Annual population growth in songbirds can be particularly sensitive to post-fledging survival, but research and management are frequently biased toward the nesting stage. Post-fledging information is particularly scarce for species breeding in desert bird communities, many of which have collapsed in recent decades. During 2017–2019 at Sevilleta National Wildlife Refuge, New Mexico, USA, we used radio telemetry to monitor survival, movements, and habitat associations of 90 fledgling Gray Vireos (Vireo vicinior), a desert-dwelling species of conservation concern. We used logistic exposure models to investigate the relationship between fledgling survival and habitat features at two spatial scales. Overall, we estimated that 51 ± 8% of fledglings survived the monitoring period. All mortalities occurred during the first 12 days post-fledging and were attributed to predation and environmental exposure. In daily survival models focused on predation mortalities, age was the strongest predictor of survival. Daily survival rate was not related to any habitat variables we measured. Percent tree cover used by birds during the first 12 days post-fledging was similar to that of nesting sites and greater than that of random locations. Similarly, fledglings occupied individual trees and shrubs with lateral vegetation cover similar to that of nest locations. Minimum daily distance traveled, distance from nests, and variance associated with these measures, all increased with age. Except for the use of a larger area, habitats used by Gray Vireos during the post-fledging period were similar to those used for nesting in our study population, indicating that maintenance of large patches of moderately dense juniper is desirable for this species. More study is needed from populations in less pristine and more heterogeneous landscapes. More broadly, given the importance of first-year survival in demographic models and the declines of dryland birds, information is needed on the post-fledging period of many desert songbirds.