Main aerial top predator of the Andean Montane Forest copes with fragmentation, but may be paying a high cost

Abstract

Large raptors are the most mobile top predators in fragmented landscapes and, consequently, they are key components of ecosystems. However, large raptors (e.g. eagles), requiring large areas of forested habitat, are also among the most threatened groups of raptors in the world and are directly and indirectly affected by habitat loss and fragmentation. The Black-and-chestnut Eagle ( Spizaetus isidori ) is a forest dependent species with a long period of natal dispersal. Here, we aim to assess home range size, mortality, and habitat selection of juvenile Black-and-chestnut Eagles during their natal dispersal in three populations within fragmented landscapes of the Tropical and Subtropical Andean Montane Forests of South America. During the first year of natal dispersal, juveniles occupied large home ranges (mean = 996.3 km 2 ; SD± 606; range = 294–2130 km 2 ). While juvenile eagles made their natal dispersal through fragmented landscapes, they consistently selected areas with higher remaining forest cover, medium elevations, and steeper slopes than the mean available in the landscape. Our study showed that juvenile eagles can tolerate a certain level of fragmentation during the natal dispersal period, although they also face high mortality during this same period. Four of the six (67 %) tagged juvenile eagles died during the study period. The high mobility of juvenile eagles may help maintain key ecosystem functions within fragmented landscapes of South America. In order to maintain viable populations of this top predator, it is urgent to mitigate non-natural mortality, mainly from direct human persecution, in fragmented landscapes. • Andean Montane Forests has lost around a half of its original vegetation cover. • Black-and-chestnut Eagle ( Spizaetus isidori ) is a highly mobile avian top predator. • Black-and-chestnut Eagle copes with fragmentation of the Andean Montane Forests. • Eagle mortality is very high and it is probably derived of habitat loss and fragmentation. • Understanding how top predators cope with fragmentation is needed for management.