Secretive flight behaviour of Golden Eagles (Aquila chrysaetos) in the vicinity of their nest

Abstract

Cover photo: Golden Eagle Aquila chrysaetos. Photo: Henning Dunker.

During breeding, most birds have to visit and leave the nest regularly to forage or to provision young. Nesting activity may help competitors or predators to locate the nest and offspring, selecting for parents to behave secretively. The present study reports observations of secretive flight behaviour of Golden Eagles Aquila chrysaetos during a long-term study in Norway based on more than 1500 hours of observation in the nesting areas of 16 pairs of eagles. By a combination of absence from the nest and secretive flights, the eagles seemed to avoid being observed near their nest, as shown by observations of 14 cases of secretive flights from 10 nesting areas. Silhouettes against the sky near the nest seemed to be avoided by the eagles, either by downhill flight in the forest below the nest and skyline, or by a fast approach to the nest, the latter either by a sideway descent or by falling like a stone from a high altitude above the nest within a few seconds. Secretive behaviour may help to avoid long-distance discovery and nest predation, in particular by intruding non-territorial eagles, but also by other raptors and Ravens Corvus corax, as well as to avoid disturbance by humans. Secretive behaviour creates serious challenges for monitoring of Golden Eagle populations, where each pair of eagles usually have several nest sites and where often less than 50% of the pairs are breeding in a given year.