Survival rates of young birds during the period between nest departure and their first breeding season is an important but difficult statistic to measure because of low natal site fidelity, especially for long-distance migrants. From 2002 to 2008, we conducted a capture-mark-resight study of Eastern Kingbirds (Tyrannus tyrannus), a Nearctic-Neotropical migrant, at Malheur National Wildlife Refuge, Oregon, to estimate juvenile (SJ) and adult (SA) survival. The return rate of juvenile kingbirds was high (0.224) and not significantly different from program MARK's estimate of SJ (0.291). On average, and for both sexes, program MARK's estimate of SA for birds banded as nestlings (0.64) was similar to that for birds first banded as adults (0.65). Enumeration methods and MARK yielded similar estimates of SA, especially for males banded as adults. We attribute the similarity of resighting rate of birds banded as nestlings to SJ and the similarity of SA estimated using program MARK and by enumeration methods to the high site fidelity of most juvenile and adult kingbirds at our ecologically isolated study site. An independent estimate of SJ calculated using local estimates of population growth and average annual production of young per year suggested that true SJ and SA were probably slightly higher than program MARK's estimates because of undocumented permanent emigration, especially of birds first banded as adults. Demographic balancing suggests that true SA and SJ were roughly 0.70 and 0.30, respectively. In general, our multiple estimates of SJ were similar. However, program MARK estimates of SJ tended to be lower than those produced by demographic balancing. Because of the difficulty in differentiating permanent emigration and mortality, and the affect it has on empirical estimates of survival, we urge researchers to use multiple methods of survival estimation, when possible, to validate the precision of their estimates.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics