Uncertainty and Precaution in Estimating the Population Size of the Philippine Eagle Available to Purchase

Other than the special case of the endangered California Condor (Gymnogyps californianus), no other large raptor has a distributional range as small as that of the Philippine Eagle (Pithecophaga jefferyi). Whereas the extent of occurrence (EOO) of the rather bigger Harpy Eagle (Harpia harpyja) is 15.5 million km² and that of the rather heavier Steller’s Sea-Eagle (Haliaeetus pelagicus) is (when breeding) 3 million km², the Philippine Eagle is crowded into a comparatively restricted 550,000 km² (BirdLife International 2024); indeed, the four islands that make up the bird’s range—Luzon, Samar, Leyte, and Mindanao—have a combined area of only 215,000 km². Given that large predatory species live at relatively low densities and necessarily possess large ranges (Colinvaux 1978), the situation of the Philippine Eagle is particularly unusual. Of three early estimates of the species’...