Strontium Isotopes are Consistent With Low-Elevation Foraging Limits for Henst's Goshawk

Apex predators play critical roles in the ecosystems they inhabit. Unfortunately, little is known about movement patterns for many species. This information is critical for evaluating vulnerability to habitat loss and the adequacy of existing or proposed protected areas. Strontium isotope ratios (Sr-87/Sr-86) in prey remains reflect the geology where individuals lived and were killed, and can be used to identify foraging ranges for predators. We tested the degree to which Sr-87/Sr-86 in consumed lemurs (Lemuroidea) can be used to track foraging ranges for Henst's goshawk (Accipiter henstii) at Ranomafana National Park (RNP), eastern Madagascar, Africa. This large-bodied endemic accipiter is sparsely distributed and rarely observed outside of forest or at elevations >1,200m. A geologic boundary divides lower and higher elevations at RNP: Precambrian migmatite is at lower elevations within and to the east of RNP and Precambrian metasediments are limited to higher elevations in southwestern RNP. We collected foliage from trees and understory plants to establish Sr-87/Sr-86 for both geologies, and remains from 19 depredated lemurs from 4 hawk nests located along the eastern edge of RNP. Leaves from metasediments have greater Sr-87/Sr-86 than leaves from migmatite. Sr-87/Sr-86 for lemur bones suggests that 18 of the 19 predated individuals came from forests underlain by migmatite. Thus, strontium isotope data suggest that Henst's goshawk primarily hunted on migmatite at RNP, which supports a growing body of evidence that this species forages at elevations below approximately 1,200m. Most reserves in eastern Madagascar protect forest at higher elevations. Conserving remaining forest and revegetating denuded land at lower elevations will likely be critical for survival of this species. Understanding mobility patterns is crucial for managing predator populations. Isotopic analysis of prey is a noninvasive method for monitoring foraging ranges that complements existing approaches. This geochemical tool is readily adaptable to other systems and species. (C) 2017 The Wildlife Society.