Between-Habitat Movement of Dusky-Footed Woodrats and Vulnerability to Predation

Abstract

Management of northern spotted owls (Strix occidentalis caurina) in northwestern California is aided by knowledge of its prey base, the dusky-footed woodrat (Neotoma fuscipes). From late April through September 1990, we radiotracked 25 dusky-footed woodrats representing both sexes and a cross section of age classes (ad, subad, and juv). Animals were captured in sapling/poletimber shrubfields resulting from past clearcut timber harvest. In northwestern California woodrats reach their highest densities in this seral stage. During evening radiotracking sessions, we detected intermittent, short distance movements of juvenile and subadult males and females, and adult females from shrubfields into adjacent old-growth forests occupied by spotted owls. None of the radiotagged woodrats permanently emigrated to older-aged forests during our study period. Between-year emigration from shrubfield to old forest, however, was documented for marked individuals. Our telemetry results indicate that woodrats are not averse to crossing sharp ecotonal boundaries from shrubfields into adjacent old forest, into canopy openings in these forests, or into natural openings within dense shrubfields. A substantial number of our radiotagged woodrats were killed by predators, with carcasses most often (5 of 9 depredated woodrats) found in adjacent old forest. These observations suggest that during these between-habitat forays, woodrats may be more vulnerable to avian and mammal predators. Therefore, to some degree, the existence of brushy shrubfields adjacent to older forest may increase the availability of woodrats to predators, such as spotted owls, that exploit prey from a variety of habitats but spend the majority of their time hunting in late seral stage forests.