Home-Range Characteristics of Spotted Owls in Northern Arizona

Abstract

We studied home-range characteristics and movements of Mexican spotted owls (Strix occidentalis lucida) in northern Arizona. Mean home-range size was 648 ha for 8 individuals and 847 ha for 3 mated pairs. Pair home ranges contained a mean of 403 ha of old-growth forest. Home-range size was positively correlated with elevation, amount of old-growth forest, and percentage of old-growth forest within the home range. Topography did not directly constrain home-range size, but did influence location of activity centers; i.e., areas that received heavy and repeated use by owls. All owls had activity centers located in old-growth forests on steep slopes, and visited other portions of the home range infrequently. On average, 60 and 80% of individual locations fell within only 21 and 47%, respectively, of a home range. Two owls left the study area from November to April and >3 others remained on or near their summer range throughout the year. Owls showed seasonal shifts in use areas with the net result that year-round home ranges were larger than the areas used during any 1 season. J. WILDL. MANAGE. 53(4): 1159-1165 The spotted owl is most common in old-growth coniferous forests in the Pacific Northwest (Gould 1977, Marcot and Gardetto 1980, Forsman et al. 1984). Owl populations appear to be declining throughout this region as timber harvest reduces the amount of old-growth forest available (Gould 1977, Forsman et al. 1984). Little is known about the habitat requirements of the Mexican subspecies of the spotted owl, which inhabits rocky canyonlands and forested highlands in the southwestern United States and Mexico (Ganey et al. 1988). The Mexican subspecies is found primarily in unlogged mixedconifer forest in Northern Arizona, and could be influenced by timber harvest in this region (Ganey and Balda 1989). Information on habitat requirements of this subspecies is needed to evaluate the potential effects of timber harvest on owl populations and develop guidelines for habitat management. We report on home-range size, habitat composition within the home range, spatial use patterns, and seasonal movements of spotted owls in northern Arizona. We thank J. Stephenson for assistance in radiotracking owls; his careful work and attention to detail under difficult field conditions was greatly appreciated. N. L. Dodd and D. Aubuchon assisted in trapping and tracking owls in the White Mountains, and W. L. Eakle assisted in trapping. L. C. Ganey spent many hours analyzing home-range data. Radio transmitters and receivers were provided by D. R. Patton, T. G. Grubb, and G. C. Bateman; C. N. Slobodchikoff provided the home-range program. Comments by G. C. Bateman, P. R. Krausman, and 2 anonymous reviewers improved the pap r. This study was supported by the U. S. Forest Service (USFS), Southwest Region, through an agreement with the Arizona Game and Fish Department, Nongame Branch. We thank E. L. Fisher and R. L. Glinski for administering this agreement. Additional funding was provided by the National Wildlife Federation, the Arizona Wildlife Foundation, and the Arizona Wildlife Federation.