Distribution and Abundance of Sandhill Cranes Wintering in Western Texas

Abstract

Population characteristics and nest-site preferences of 11 species of cavity-nesting birds were studied in the Olympic National Forest (ONF) of northwestern Washington in the spring and summer of 1979-80. We characterized breeding populations in four different forest successional stages where either high or low densities of snags occurred. Species richness (N = 13 vs. N = 9), densities (P < 0.01), and diversities (P < 0.01) of cavity-nesting birds increased with increasing snag densities. Active cavity-nests were five times more numerous on the 1980 plots (Snag Plots) than the 1979 plots (Clean Plots). Snag densities on the Snag Plots varied from 13.8/ha in a clear-cut to 97.1/ha in 25-50-year-old second-growth stand. Clean Plots contained from 0.5 snags/ha in a clear-cut to 37.3/ha in old-growth. Hairy woodpeckers (Picoides villosus), a primary cavity-nester, selected western hemlock (Tsuga heterophylla) snags for nest sites. In contrast, broken-topped Douglas-fir (Pseudotsuga menziesii) snags were preferred by secondary cavitynesters. The average diameter at breast height (dbh) for active nest trees was substantially greater than the mean dbh for sampled snags in the ONF. Snags appear to be a limiting factor for breeding cavity-nesting bird populations. We discuss management recommendations for cavity-nesting birds in the ONF. J. WILDL. MANAGE. 49(1):255-263 The rapid harvesting of old-growth and shortening of harvest rotation cycles in the Pacific Northwest western hemlock-Douglas-fir forests disrupt avifauna. Several authors have shown that snag removal during intensive forest management is highly detrimental to cavitynesting birds (Balda 1975, Thomas et al. 1976, Evans and Conner 1979, Short 1979). Snag removal eliminates nest and roost sites that are crucial for successful breeding and overwinter survival. Although specific nest-site characteristics have been studied in other parts of the western United States (Bull and Meslow 1977, McClelland 1977, Mannan et al. 1980, Raphael and White 1984), only this study reports intensive research on cavity-nesting populations in the moist coastal climate of Washington. The objectives of our study were to: (1) estimate densities and diversities of cavity-nesting birds in four forest successional stages in northwestern Washington; (2) compare the influence of high and low snag densities in the successional stages on cavity-nesting populations; and (3) determine the nest-site requirements for breeding cavity-nesting birds. This research was funded by the U.S. For. 'Present address: Washington Department of Game, 5405 N.E. Hazel Dell Ave., Vancouver, WA 98665. This content downloaded from 207.46.13.166 on Thu, 07 Jul 2016 04:14:24 UTC All use subject to http://about.jstor.org/terms