Domestic cats have been introduced to many of the world‘s islands where
they have been particularly devastating to insular wildlife which, in most
cases, evolved in the absence of terrestrial predatory mammals and feline
diseases. We review the effects of predation, feline diseases, and the life
history characteristics of feral cats and their prey that have contributed to the
extirpation and extinction of many insular vertebrate species. The protozoan
Toxoplasma gondii is a persistent land-based zoonotic pathogen hosted by
cats that is known to cause mortality in several insular bird species. It also
enters marine environments in cat feces where it can cause the mortality of
marine mammals. Feral cats remain widespread on islands throughout the
world and are frequently subsidized in colonies which caretakers often
assert have little negative effect on native wildlife. However, population
genetics, home range, and movement studies all suggest that there are no
locations on smaller islands where these cats cannot penetrate within two
generations. While the details of past vertebrate extinctions were rarely
documented during contemporary time, a strong line of evidence is
emerging that the removal of feral cats from islands can rapidly facilitate the
recolonization of extirpated species, particularly seabirds. Islands offer
unique, mostly self-contained ecosystems in which to conduct controlled
studies of the effects of feral cats on wildlife, having implications for
continental systems. The response of terrestrial wildlife such as passerine
birds, small mammals, and herptiles still needs more thorough long-term
monitoring and documentation after the removal of feral cats.
