ADULT AND JUVENILE SURVIVAL OF BLACK-CAPPED VIREOS WITHIN A LARGE BREEDING POPULATION IN TEXAS

Abstract

We used mark-recapture and information-theoretic model selection methodologies to estimate survival and recapture probabilities for the federally endangered Black-capped Vireo (Vireo atricapilla) at Fort Hood Military Reservation, Texas, during 1997–2006. Adult survival was time-dependent and ranged from 0.36 to 0.60. Although we found no support for sex-specific differences in adult survival, recapture probability was greater for males (0.83) than females (0.58). Adult survival differed among three study areas, which could be indicative of site-specific differences in habitat quality. Survival of juveniles from their hatching year to the following spring was dependent on age at banding. Survival of juveniles banded as nestlings or soon after fledging was low (0.10). The survival estimate for juveniles banded after postfledging independence was substantially higher (0.42). Because juvenile survival is difficult to estimate for passerines, it is often set at an arbitrary value such as one third or half of adult survival. Our survival estimate for juveniles banded after postfledging independence was higher than suggested by either of these commonly used guidelines. We acknowledge that our survival estimates are probably biased low because we could not differentiate between dispersal and mortality. Adoption of a study design that includes core areas where vireos are marked and resighted in subsequent years as well as surrounding resight-only areas would presumably improve survival estimates for both adults and juveniles. More robust estimates of survival could greatly improve population viability analyses for this endangered species.