Feral Pigs Facilitate Hyperpredationby Golden Eagles and Indirectly Cause the Decline of the Island Fox.
G.W. Roemer, T.J. Coonan, D.K.Garcelon, J. Bascompte, and L. Laughrin. 2001
Animal Conservation, 4: 307-318.
accommodation in BathABSTRACT: Introduced speciescan compete with, prey upon, or transmit disease to native forms, resultingin devastation of indigenous communities. A more subtle but equally severeeffect of exotic species is as a supplemental food source for predatorsthat allows them to increase in abundance and then overexploit native preyspecies. Here we show that the introduction of feral pigs (Sus scrofa)to the California Channel Islands has recently attracted and sustainedan unnaturally large breeding population of golden eagles (Aquila chrysaetos),a native predator. The resulting increase in predation on the island fox(Urocyon littoralis) has caused the near extirpation of three subspeciesof this endemic carnivore. Prior to the 1990's, golden eagles were onlytransient visitors to the Channel Islands. New evidence, including an increasein eagle sightings, observations of a family group, and the discovery ofthe first golden eagle nest in 1999, confirm that eagles recently colonizedthe northern islands and that their population has expanded. A two prey- single predator logistic model supports the premise that golden eaglesare sustained by the large population of feral pigs and caused the populationdeclines of the island fox. Fox populations on the northern Channel Islandshave declined by 90% in only six years and have an estimated 50% chanceof persistence over the next decade. If feral pigs and golden eagles arenot removed from the islands, hyperpredation on foxes will likely causetheir extirpation.
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