Roost site characteristics of northern spotted owls in the nonbreeding season in central Washington

To evaluate habitat important to northern spotted owls (Strix occidentalis caurina) away from the nest stand, we used radio telemetry to locate adult owls at diurnal roosts during the nonbreeding season (September 1-March 15, 1994-1997). We recorded physiographic variables and measured within-stand structural characteristics within nested circular plots centered on roost trees. We then compared owl use plots to random plots selected within suitable habitat and inside the approximated home ranges of the 14 (7 male, 7 female) owls studied. Spotted owls selected older forest over young forest. Owls selected sites lower in elevation, with larger tree diameter at breast height (dbh), fewer trees/ha, greater canopy cover, less cover of low shrubs, and fewer pieces of down wood than random locations. Females used old-growth and mature forest to a greater degree than males. Fewer trees/ha, less cover of low shrubs, and fewer pieces of down wood/transect best discriminated roost sites from random sites. These characteristics are not indicative of stand conditions thought to maximize prey density. Results may indicate selection of specific sites for roosting. However, because spotted owls opportunistically take prey from diurnal roosts and often roost in foraging stands, they may also be selecting for site characteristics that facilitate the capture of prey.