Primary Cavity-Site Selection by Birds

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Abstract
Current recommendations for snag management, which focus on characteristics of individual snags or stocking levels in forests managed for timber production, not only obscure the importance of forest characteristics surrounding a potential nesting site but also fail to meet the management objectives or abilities of the small landowner. During the summers of 1978 and 1979, a random sample of 816 snags (standing dead trees) was studied in central New York [USA]. Sixty-seven percent of the sample was in mature maple (Acer spp.)-ash (Fraxinus spp.)-elm (Ulmus spp.), the remainder was in 2nd growth woodland. A set of 21 characteristics of snags and 19 characteristics of forest sites was analyzed to determine which best predicted bird use. Use was defined as the presence of .gtoreq. 1 bird cavity in a snag or a forest site. Forest characteristics were sampled in randomly located 0.049-ha circles (N=61) in 1979. Stepwise logistic regression revealed that forest characteristics (total snag basal area, tree species diversity, and number of tree species) were more reliable predictors of bird use than were snag characteristics (diameter at breast height [dbh], amount of bark, height, and species). Snag management based on selecting suitable forest sites and on maintaining or creating suitable snags within those sites is recommended. Use of logistic regression models by field managers is discussed.

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