Survival Estimates and Cause of Mortality of Golden Eagles in South-Central Montana

Abstract

Golden Eagles are a long-lived, wide-ranging bird of conservation concern in North America. To create a comprehensive conservation strategy, managers and researchers need to know the primary causes of mortality and must have reliable survival estimates. We monitored nesting Golden Eagles in a 2700 km2 area of south-central Montana from 2010–2017. As part of our effort, we fitted 16 adult and 13 nestlings with platform terminal transmitters for satellite telemetry. We determined causes of mortality from recovered Golden Eagles and, using multi-state models in program MARK, we estimated monthly and annual survival probabilities. We confirmed five total mortalities, including two cases of lead toxicity, one occurrence of intraspecific aggression, and two mortalities with unknown cause. The monthly survival estimate of adult Golden Eagles in our study area was 0.994 and the annual adult survival probability was 0.930. The monthly survival probability estimate from birds transmittered as nestlings was 0.991 and the annual survival estimate was 0.897. Lead toxicity and intraspecific aggression are known causes of Golden Eagle mortality, but the birds we tracked died from lead toxicity at a higher rate than would be expected based on results from other studies. The survival probability estimates from the Golden Eagles we monitored were higher than reported estimates from other locations. Further, the information we provide can assist with the development of population matrices and increase our knowledge on causes of Golden Eagle mortality.