INFERRING BREEDING SUCCESS THROUGH RADIOTELEMETRY IN THE MARBLED MURRELET

Abstract: Demographic parameter estimates are essential for understanding population ecology and developing management plans for species of concern. We inferred measures of breeding success using radiotelemetry in the marbled murrelet (Brachyramphus marmoratus), a secretive, forest-nesting seabird, from 1998 to 2001 in Desolation Sound, British Columbia, Canada. Our estimates of mean annual nesting success and fecundity (0.19–0.23 female offspring/adult female/yr) are among the highest reported for the species. We suspect that our estimates are high compared to previous estimates in our study area (Manley 1999), primarily because of our higher success in areas inaccessible to ground-based human observers. We detail how behavior-based inferences of activity at different reproductive stages did not differ between confirmed nest sites and suspected nest sites that were physically inaccessible to us. We were able to accurately predict initiations of breeding and incubation success from the duration of adults' repeated daily shifts from the ocean to their inland nest sites. Chick-rearing success was accurately predicted by visitation rates of adults during provisioning. We discuss the assumptions and potential biases of our methods and their effects on our results. Our method may overestimate early breeding failure, but it likely provided unbiased fecundity estimates for our population. Accurately inferring breeding success through radiotelemetry is costly and labor intensive. However, radiotelemetry could provide crucial demographic information once thought impossible to obtain for secretive breeding species.