Population dynamics of introduced rodents in Hawai'i Volcanoes National Park 1986-1990

Abstract

We determined seasonal and geographical distribution patterns for four species of introduced rodents in Hawai‘i Volcanoes National Park from 1986-1990. We surveyed black rats (Rattus rattus), Polynesian rats (R. exulans), Norway rats (R. norvegicus) and house mice (Mus musculus) along an elevation gradient ranging from 90–1,820 m above sea level in five different sites using baited snap traps. Rodent community structure differed by elevation: there were more mice at montane sites and more Polynesian rats in the lowlands. We found that breeding occurred throughout the year for all species at all sites but that seasonal peaks in reproductive activity were common. Reproduction tended to be more common in the summer months at higher elevation sites and in the winter months at lower elevations. Rodents of all species were more abundant in our study in the winter than in the summer, but the differences were not significant. The overall sex ratio did not vary from a 1:1 ratio, but seasonally there were differences in sex ratio which varied with species and site. We calculated the minimum distance traveled from an assessment line and found that larger-bodied species traveled longer average distances. Pelage color in black rats was darkest in wet forest which may have adaptive value. Black and Polynesian rats were widespread in almost all habitat types, whereas mice were limited to dry and mesic sites; Norway rats were the rarest component of our sampling and found only in wet montane forest (‘Ōla‘a Forest).