ECOLOGY OF INTRODUCED SMALL MAMMALS ON WESTERN MAUNA-KEA, HAWAII

I studied the distribution, diet, and patterns of habitat utilization of introduced rodents (black rats, Rattus rattus, and house mice, Mus musculus) on western Mauna Kea, the habitat of several Hawaiian honeycreepers (subfamily Drepanidinae). Distribution and habitat utilization were investigated at four elevational ranges along a gradient of 1,600-3,000 m. Rodent distribution appears to be determined by microhabitat availability. Both rats and mice preferred microhabits of dense tree stands and tall grass over open spaces, and their abundance declined with the progressive reduction of these preferred microhabitats with increasing elevation. Black rats were rare, and their numbers were at least an order of magnitude lower than that of the palila (Loxioides bailleui) and common amakihi (Hemignathus virens). Rats had the lowest densities in areas of highest abundance of palila. Palila and black rats also showed segregated microhabitat preferences. Diets of feral cats (Felis sylvestris), mongooses (Herpestes auropunctatus), and mice showed no evidence that they prey on eggs, nestlings, or adults of endemic birds. These trends give no indication that introduced mammals could be important predators of honeycreepers and suggest that small mammals may be tracking a different set of resources or conditions from those of endemic birds.