Post-fledging survival of Marbled Murrelets Brachyramphus marmoratusestimated with radio-marked juveniles in Desolation Sound, BritishColumbia

摘要

For many birds, juvenile survival rates are the least-known demographic component. However, such estimates are important in the construction of population projection models. Here we report the first estimates of local survival for juvenile Marbled Murrelets Brachyramphus marmoratus, an alcid species of conservation concern in the Pacific Northwest. We estimated the survival of 34 radio-tagged individuals to be 0.8621 (95% CI 0.7250 - 1.001) during an 80 day period post-fledging. When extrapolated over a year, under the assumption of constant survival, this translates into an annual survival rate of 0.51. In the absence of information on the influence of the transmitters on survival, our estimates were calculated with the assumption that there were no effects. Our estimates do not include fledging or early post-fledging mortality. A high proportion of radioed juveniles were censored throughout the study, and we suggest that natal dispersal may account for this. The extrapolated annual survival rate is lower than values previously used in demographic models for this species, but this work provides the first data-based evaluation of juvenile survival for the Marbled Murrelet.