Apparent Survival of Territorial Golden Eagles Using Non-Invasive Genetic Profiling

Conservation efforts for large raptors require robust estimates of fecundity, age at maturity and survivorship and population trajectories are often particularly sensitive to change in adult survival rates. Our study estimated apparent survival rates in territorial range-holding Golden Eagles Aquila chrysaetos in Scotland, based on DNA extracted from moulted feathers to profile individuals genetically: the first study for this species using the method. Feathers were collected at or close to nest sites involving 104 territorial individuals, across 4 years (2006-2009), with repeat-sampling in 21% of 442 occupied home ranges. Genetic profiles identifying individuals' detection/non-detection were analysed to estimate annual apparent survival rates using Cormack-Jolly-Seber models. Our models included sex, as male survival was expected to be lower through greater male parental burdens, and two regions, the Outer Hebrides and the Inner Hebrides/Highlands, that host separate sub-populations. Lower survival was expected in the Outer Hebridean archipelago through negative density-dependence created by globally high densities in this isolated sub-population. Estimates of male annual apparent survival rates (0.774-0.808) were markedly lower than females in both regions (0.878-0.882). Encounter rates of males (0.441-0.454) were also lower than females (0.639-0.754), probably because males spend less time near nest sites. Male life expectancy was ~50% lower in both study regions. We found no support for different regional survival. We recorded a few instances of breeding dispersal, mostly females moving to neighbouring territories. Illegal killing probably had negligible influence on apparent survival estimates, because the DNA method is not well-suited for detecting persecution in Scotland. Our estimates of apparent survival were probably close to true natural survival. Annual rates for females were similar to previous estimates derived for the same 'adult' age/status class, which utilised other methods but did not separate the sexes. Sex difference in adult survival should be a feature of future studies of raptors and its role in demography and conservation.