Management and conservation implications of Blakiston's fish owl (Ketupa blakistoni) resource selection in Primorye, Russia.

Abstract

The Blakiston's fish owl (Ketupa blakistoni) is a large owl associated with riparian old-growth forests in northeast Asia. Despite its status as a charismatic endangered species, specific conservation and management efforts for the species in Russia are limited. This is because resource use by these secretive owls is poorly known. To address this information deficit, I analyzed resource selection by these owls within a 20,213 km2 study area in Primorye, Russia. Resource selection studies often begin by defining the spatial extent of a home range and then quantifying use of available resources within that home range. For animals that use habitat that are defined by linear environmental features, such as Blakiston's fish owl, traditional home range estimators often overestimate home range size, which can lead to spurious conclusions about resource availability and selection. I used a synoptic model of space use to define Blakiston's fish owl seasonal and annual home range size and within-home range resource selection, and compared results to traditional home range estimators. I also examined nest tree and foraging site selection at 14 nest and 14 foraging sites using linear discriminant analysis. I then identified areas with the highest predicted probability of use by owls to prioritize areas for conservation and management. Fish owl home range was different among most seasons, and estimated home range sizes based on the synoptic model were more biologically-realistic than kernel density-based home range estimators. Mean annual home range size (± standard error) for all fish owls was 15.0 ± 3.7 km2 (n = 7) using the synoptic model, and 38.8 ± 15.4 km2 using kernel density estimators. By season, winter home range was 7.0 ± 3.3 km2 vs. 5.9 ± 2.3 km2 (n = 3 owls; synoptic model vs. kernel density estimator); in spring 13.9 ± 5.2 km2 vs. 29.5 ± 20.4 km2 (n = 7); in summer 11.6 ± 2.8 km2 vs. 33.2 ± 11.9 km2 (n = 6); and in autumn 25.2 ± 13.4 km2 vs. 85.1 ± 56.0 km2 (n = 5). Fish owls selected home ranges that were within valleys, were close to water, and had a greater number of river channels than available sites. Old trees and riparian old-growth forest were the primary discriminating characteristics at both nest and foraging sites, respectively. Large trees were likely necessary as owl nest sites because of the bird's large body size. Moreover, old forests have many large trees that facilitated recruitment of large woody debris in rivers, which created suitable habitat for the owl's primary prey: salmonid fish. Based on resource selection functions I predicted that 54 fish owl territories could occur within my study area. I found that the reserve network contained only 21% of primary fish owl habitat and potentially contained only 7 fish owl territories. I also found that 39% of primary habitat was within current logging leases, which was capable of supporting habitat equivalent to 18 fish owl territories. The remainder of primary habitat (40%) was on federal land not presently protected or within logging leases, and potentially contained 29 fish owl territories. The current protected area network, by itself, will be insufficient to conserve fish owls because so few owl territories are actually protected. Therefore, I developed specific conservation recommendations within logging leases based on the observed resource selection patterns by the owls. My recommendations include protecting specific locations within potential territories, maintaining integrity of riparian areas, modifying road construction techniques, and closing old logging roads to reduce human access. These simple measures have the potential not only to conserve fish owls but also many other species, making this owl an effective umbrella species for the riparian ecosystems of the region.