Ecology of an Invasive Predator in Hawaii

Cats (Felis catus) brought to Hawai`i in the 1700s now occupy most habitats throughout the islands, including montane and sublapine zones. We studied home range, population genetics, diseases, and diet of feral cats on Hawai`i Island. Feral cats on Mauna Kea live in low densities and exhibit some of the largest reported home ranges. While 95% kernel home range estimates for 4 males ( x = 1418 ha) were nearly twice as large as 3 female home ranges ( x = 772 ha), one male maintained a home range of 2050 ha. Population genetics revealed that Mauna Kea may be a source population for feral cats on Mauna Loa and Hawai`i Volcanoes National Park (HAVO). Assignment tests provided strong evidence for male-biased dispersal from Mauna Kea to Mauna Loa. Mauna Kea cats exhibited high seroprevalence for toxoplasmosis (37.3%) and feline leukemia virus (FeLV; 16.2%) distributed among all age and sex classes. Feline immunodeficiency virus (FIV) occurred only in adult males comprising 8.8% of the overall population. We found that cats on Mauna Kea primarily consumed birds, present in 69% of digestive tracts, whereas birds were in only 28% of samples from HAVO. Within HAVO, prey use differed between K ī lauea and Mauna Loa. On Mauna Loa, more feral cats consumed small mammals (89%), primarily rodents, than on K ī lauea Volcano (50%). Mice (Mus musculus) were the major component of the feral cat diet on Mauna Loa, whereas Orthoptera were the major component of the diet on K ī lauea. A digestive tract from Mauna Loa contained a mandible set, feathers, and bones of an endangered Hawaiian Petrel (Pterodroma sandwichensis). Abundant birds on Mauna Kea may maintain large numbers of feral cats that disperse long distances. Abundant rodents found in Mauna Loa digestive tracts may also support cats that then take advantage of breeding petrels.