HABITAT SELECTION BY NORTHERN SPOTTED OWLS - THE CONSEQUENCES OF PREYSELECTION AND DISTRIBUTION

We tested three predictions of a hypothesis that states Northern Spott ed Owls (Strix occidentalis caurina) select habitat according to the d istribution of their primary prey. Our predictions were that Northern Spotted Owls should (1) select larger (> 100 g) species among the asse mblage of available prey, (2) select habitats according to the distrib ution of large prey, and (3) the owl's reproductive success should be influenced by the availability of large prey. We also evaluated the po tential energetic value of several prey species. We found that Norther n Spotted Owls (n = 11 pairs and 1 single male) in northwestern Califo rnia differentially selected the dusky-footed woodrat (Neotoma fuscipe s), a moderately large sigmodontine rodent ((x) over bar mass = 232 g) . When foraging, owls selected late seral forest edge sites where dusk y-footed woodrats were more abundant. Although the relationship betwee n site selection, prey abundance, and the owl's breeding success was n ot statistically significant, the average abundance of dusky-footed wo odrats at sites foraged by breeding owls ((x) over bar = 11.4 woodrats 100-trap-nights(-1)) was greater than at sites foraged by nonbreeding owls ((x) over bar = 4.7 woodrats 100-trap-nights(-1)). We estimated that a male Spotted Owl would require 150,015 to 336,232 kJ over a 153 -day period while helping to produce one young, and concluded that the selection of woodrats provided a potential energetic benefit over the use of other prey. These findings provide a partial explanation for t he owl's affinity for late seral forests.