Mexican Spotted Owl reproduction, home range, and habitat associations in Grand Canyon National Park

Abstract

Mexican spotted owls (Strix occidentalis lucida) are nocturnal avian predators that are widely distributed in the southwest U.S. and northern Mexico. In 1993, the lucida subspecies was listed as threatened in response to concern over the loss of forest habitats to which the owl is widely associated. However, in the northwestern corner of their range spotted owls primarily inhabit steep-walled rocky canyons. Owl populations inhabiting this region have received less attention than populations using forests, although, canyon populations are important to the persistence of the subspecies, and are subject to different environmental pressures. I investigated the breeding ecology and home range characteristics of Mexican spotted owls within Grand Canyon which supports both forest and rocky canyon habitat. During the study from 2004 - 2006, female fecundity (mean = 0.86), calculated as the number of female fledglings per paired female, was relatively high compared to values reported previously for Mexican spotted owls. Five adult male owls were radio-tracked during the breeding season. I used minimum convex polygons and fixed kernel estimates to describe home range size (mean = 356 ha and 372 ha, respectively) and generated adaptive kernels to describe areas of concentrated use within home ranges. I used GIS to describe vegetation and geology cover types associated with owl use areas. This information was used to determine if spotted owls used landscape cover types disproportionately to their availability. At a landscape level, spotted owl telemetry locations were positively correlated with piñyon-juniper vegetation that occurred within canyons as well as with the Redwall and Muav geologic layers (p <or equal to 0.05). Home ranges were located toward the heads of tributary canyons and spotted owls were rarely observed above the rim on forested plateaus. To identify nest core areas that might aid in the species conservation I delineated 40 ha "protected core areas" around spotted owl nest sites and show that these conservation zones correlated closely to areas of concentrated use I identified using an adaptive kernel (30% isopleth) home range analysis.