Long-term breeding demography and density dependence in an increasing population of Golden Eagles Aquila chrysaetos

Abstract

International audienceFew studies have quantified the dynamics of recovering populations of large raptors using long-term, spatially explicit studies. Using data collected over 37 years in the western Italian Alps, we assessed the trends in distribution, abundance, fecundity and breeding population structure of Golden Eagles Aquila chrysaetos. Using the spatial distribution of territory centroids in 2007, we found that the spatial distribution of eagle territories was over-dispersed up to 3 km. Although population size and total productivity increased from 1972 to 2008, the proportion of pairs that laid eggs showed a strong decline, falling to no more than 50% after 2003. On average, 15% of successful nests produced two fledglings, and productivity also declined over time. No significant relationship between population growth rate and total population size was detected, but the percentage of pairs that bred and breeding success showed evidence of density dependence, as they declined significantly with increasing density. Our results suggest that density dependence, operating across heterogeneous habitats, is currently regulating this population, while the carrying capacity may still be increasing. This may explain the apparent paradox of reduced breeding effort despite increasing total productivity

The demography of a newly establishedOspreyPandion haliaetuspopulation inFrance

“…Although several recovering raptor populations such as the Golden Eagle Aquila chrysaetos in the Alps (Fasce et al . ), the Griffon Vulture Gyps fulvus in central France (Sarrazin & Legendre ), the White‐tailed Eagle Haliaeetus albicilla in northern Germany (Krüger et al . ), the Bearded Vulture Gypaetus barbatus in northern Spain (Oro et al .…”

“…Evidence for density‐dependence on productivity and proportion of breeders was found in the Golden Eagle (Fasce et al . ) and in the Bearded Vulture (Carrete et al . , Oro et al .…”

Government-sponsored Falconry Practices, Rodenticides, and Land Development Jeopardize Golden Eagles (Aquila chrysaetos) in Western China

“…However, the number of young that reached minimum fledging age (the standard measure of productivity for raptors, Steenhof et al 2017) was significantly lower in the W study area. Average fledging production for the C (mean ¼ 0.56, range ¼ 0.25-0.85) and E (mean ¼ 0.54, range ¼ 0.24-0.82) study areas were within the range reported in long-term studies from Alaska (mean ¼ 0.62, range ¼ 0.05-1.21;McIntyre and Schmidt 2012), Idaho (mean ¼ 0.79, range ¼ 0.34-1.38;Steenhof et al 1997), and Italy (mean ¼ 0.55, range ¼ 0.27-2.00; Fasce et al 2011), whereas average fledgling production in the W study area (mean ¼ 0.26, range ¼ 0.12-0.39) was similar to the lowest levels documented in other studies. Table 6.…”

Top‐down limitation of mesopredators by avian top predators: a call for research on cascading effects at the community and ecosystem scale

“…First, generalist mesopredators have bounced back as a result of lower hunting pressure and adaptation to anthropogenic resources in modified landscapes (Bino et al 2010), sometimes at the expense of the vulnerable specialist mesopredators (Lindstr€ om et al 1995, Henden et al 2010, Elmhagen et al 2015. In parallel, several top predators, including large carnivorous mammals and avian top predators, have recolonized previously deserted areas (Fasce et al 2011, Chapron et al 2014, Graci a et al 2015. In quite a few cases, recolonization has been assisted by reinforcement or reintroduction programmes (Dalbeck & Heg 2006, Evans et al 2009, Morandini et al 2017.…”