Demography of northern spotted owls on the H.J. Andrews study area in the central Cascade Mountains, Oregon

We initiated intensive monitoring of a North-ern Spotted Owl (Strix occidentalis caurina) pop-ulation in the central Cascade Mountains ofwestern Oregon in 1987. Our study was estab-lished to collect long-term demographic trendinformation in order to better understand thecurrent status of the Northern Spotted Owl pop-ulation in the western Oregon Cascades. In par-ticular, we wanted to determine if concerns aboutgradual population declines in conjunction withhabitat loss were well-founded (Thomas et al.1990. 1993a: USD1 1990).
The H. J. Andrews Study Area (HJA) was anideal location to examine these issues. Vegeta-tion on the area is typical of much of the forestand land-use conditions on the west slope of the Cascade range in Oregon. The area also has along history of Spotted Owl research. The first intensive study of Spotted Owl ecology, including home range size and habitat use, occurred on the HJA area and began in the early 1970s (Forsman 1980, Forsman et al. 1984). Several owl nest sites have been monitored periodically since that time. With this work came some of the first banded Spotted Owls, providing insights into the species' longevity. In addition, the first study of dispersal of juvenile Spotted Owls in Oregon was conducted on the HJA (Miller 1989), along with research on Spotted Owl prey species (Rosenberg 1991) and the influence of habitat fragmentation on owl populations (Johnson 1992).
Our objectives for this long-term monitoring study were to estimate survival based on capture-recapture methods, estimate age-specific fecundity based on direct observations of number of young fledged, and to use this information to calculate rate of population change (X) for the period 1987-1993. We also compared these results to empirical counts of territorial owls, and discuss owl population dynamics in light of remaining amounts of late seral stage forest on our study area.