Habitat Selection by Spotted Owls during Natal Dispersal in Western Oregon

Abstract

The probability of successful natal dispersal may influence the viability of northern spotted owl (Strix occidentalis caurina) populations within fragmented forests. We tested 6 null hypotheses examining the relations between habitat selection, forest fragmentation, and the probability of mortality for juvenile northern spotted owls during natal dispersal in western Oregon, 1982-85. Older forest (old-growth and mature stands) was the vegetation type used most frequently during transience (35.3%) and colonization (61.2%), and spotted owls selected closed-canopy forests over open-canopy forests during both phases of dispersal (P < 0.05). The hypotheses that spotted owl habitat selection was independent of forest fragmentation were not rejected for either transient (P = 0.51) or colonization (P = 0.43) dispersal. Likewise, net dispersal distance was independent of forest fragmentation (P = 0.92). Use of open sapling stands during transient dispersal decreased the probability of mortality (Wald test = 2.21, P = 0.03), whereas use of clearcuts during colonization dispersal increased the probability of mortality (Wald test = 1.95, P = 0.03). Net dispersal distance did not affect the probability of mortality (P = 0.67), yet a negative relation existed between dispersal distance and the amount of clearcut used during transient dispersal (P < 0.005). These results provide additional evidence of the selection of older forests by spotted owls and how their natal dispersal may be affected by harvesting such forests; particularly, that use of clearcuts may decrease the probability of successful natal dispersal.