BETWEEN-HABITAT MOVEMENT OF DUSKY-FOOTED WOODRATS AND VULNERABILITY TO PREDATION

Management of northern spotted owls (Strix occidentalis caurina) in no rthwestern California is aided by knowledge of its prey base, the dusk y-footed woodrat (Neotoma fuscipes). From late April through September 1990, we radiotracked 25 dusky-footed woodrats representing both sexe s and a cross section of age classes (ad, subad, and juv). Animals wer e captured in sapling/poletimber shrubfields resulting from past clear cut timber harvest. In northwestern California woodrats reach their hi ghest densities in this seral stage. During evening radiotracking sess ions, we detected intermittent, short distance movements of juvenile a nd subadult males and females, and adult females from shrubfields into adjacent old-growth forests occupied by spotted owls. None of the rad iotagged woodrats permanently emigrated to older-aged forests during o ur study period. Between-year emigration from shrubfield to old forest , however, mas documented for marked individuals. Our telemetry result s indicate that woodrats are not averse to crossing sharp ecotonal bou ndaries from shrubfieIds into adjacent old forest, into canopy opening s in these forests, or into natural openings within dense shrubfields. A substantial number of our radiotagged woodrats were killed by preda tors, with carcasses most often (5 of 9 depredated woodrats) found in adjacent old forest. These observations suggest that during these betw een-habitat forays, woodrats may be more vulnerable to avian and mamma l predators. Therefore, to some degree, the existence of brushy shrubf ields adjacent to older forest may increase the availability of woodra ts to predators, such as spotted owls, that exploit prey from a variet y of habitats but spend the majority of their time hunting in late ser al stage forests.