Breeders' age, nest-site characteristics and climatic conditions but not density-dependent effects determine Bonelli's Eagle breeding performance: A long-term study (2002--2021).

This article presents a long-term (2002–2021) study of Bonelli’s Eagle (Aquila fasciata) breeding performance in the eastern Iberian Peninsula, focusing on the effects of breeders’ age, nest-site characteristics, climatic conditions, and density-dependent factors. The study found a significant decline in the number of occupied territories and breeding pairs, but no evidence that negative density-dependent effects influenced breeding success or productivity. Instead, higher productivity was associated with territories occupied by adult breeders, located in milder coastal climates with higher winter precipitation and temperatures, and earlier laying dates; the presence of subadult breeders negatively affected reproduction. Additionally, variability in fledgling numbers within territories was linked to previous breeding costs and weather conditions. The findings emphasize the importance of mitigating adult mortality and conserving suitable habitats to halt population decline and improve reproductive output in this threatened top predator.