Abstract
Apex predators are threatened globally, and their local extinctions are often driven by failures in sustaining prey acquisition under contexts of severe prey scarcity. The harpy eagle Harpia harpyja is Earth’s largest eagle and the apex aerial predator of Amazonian forests, but no previous study has examined the impact of forest loss on their feeding ecology. We monitored 16 active harpy eagle nests embedded within landscapes that had experienced 0 to 85% of forest loss, and identified 306 captured prey items. Harpy eagles could not switch to open-habitat prey in deforested habitats, and retained a diet based on canopy vertebrates even in deforested landscapes. Feeding rates decreased with forest loss, with three fledged individuals dying of starvation in landscapes that succumbed to 50–70% deforestation. Because landscapes deforested by > 70% supported no nests, and eaglets could not be provisioned to independence within landscapes > 50% forest loss, we established a 50% forest cover threshold for the reproductive viability of harpy eagle pairs. Our scaling-up estimate indicates that 35% of the entire 428,800-km2 Amazonian ‘Arc of Deforestation’ study region cannot support breeding harpy eagle populations. Our results suggest that restoring harpy eagle population viability within highly fragmented forest landscapes critically depends on decisive forest conservation action.
Highlights
Apex predators are threatened globally, and their local extinctions are often driven by failures in sustaining prey acquisition under contexts of severe prey scarcity
Considering that we found no active nests in landscapes that had succumbed to > 70% forest loss (n = 34, excluding nests in riparian forest remnants), we determined an approximate threshold above which harpy eagles can no longer tolerate landscape-scale deforestation
Our data and analyses showed that forest loss is associated with severe reductions in prey delivery rates and prey biomass by adult harpy eagles to their eaglets; nestlings reared in highly fragmented areas received less food with longer intervals between consecutive feeding bouts
Summary
Apex predators are threatened globally, and their local extinctions are often driven by failures in sustaining prey acquisition under contexts of severe prey scarcity. Apex predators are sensitive to changes in the spectrum and availability of food because of their high metabolic requirements[12] They depend on stable and secure prey populations to fuel their relatively high daily survival and breeding requirements[13]. Harpy eagles are typically very long-lived; a 54 years-old wild-caught adult individual was still alive with the publication of the latest s tudbook[34] They usually show strict nest site fidelity, breeding in the same specific T-shaped emergent nest tree for several consecutive d ecades[35,36]. Studies of their breeding biology are still considered a high research priority[33] Their global distribution has contracted by 41% since the nineteenth century, and currently, 93% of their distribution range is within Amazonian Forests, their last s tronghold[10]. Leading causes explaining their rapid decline are habitat loss[10], and shooting by settlers and, to a lesser extent, reprisal for killing livestock[38,39]
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