INFLUENCE OF PRIMARY PREY ON HOME-RANGE SIZE AND HABITAT-USE PATTERNSOF NORTHERN SPOTTED OWLS (STRIX OCCIDENTALIS CAURINA)

Correlations between the home-range size of northern spotted owls (Str ix occidentalis caurina) and proportion of their range in old-growth f orest have been reported, but there are few data on the relationship b etween their home-range size and prey. The primary prey of spotted owl s are wood rats and northern flying squirrels (Glaucomys sabrinus). Wo od rats are larger and heavier than flying squirrels, and their popula tion densities tend to be much greater than those of flying squirrels. We present data indicating that the home ranges of spotted owls are s maller where their diet consists predominantly of wood rats than where it consists predominantly of flying squirrels, and the proportion of the diet consisting of wood rats and flying squirrels explained signif icant variation in home-range size. We also found a significant correl ation between home-range size and abundance of wood rats. These data i ndicate that prey species are a better predictor of home-range size th an the proportion of older forest within spotted owl home ranges in th e Klamath Province of northwestern California and southwestern Oregon, an area that is predominantly late-successional forest. Differences i n habitat use were also related to prey species. Where spotted owls fo raged for wood rats, the results indicated a preference for habitat ed ges, but where they utilized flying squirrels no such patterns were ap parent.