Nest-Site Preference of Northern Goshawks in Southcentral Wyoming

Abstract

In 1992, we studied the nest-site preference of goshawks (Accipiter gentilis atricapillus) nesting in lodgepole pine (Pinus contorta) forests of the Medicine Bow National Forest, southcentral Wyoming. For 39 active pairs of goshawks, we described nesting habitat at 3 spatial scales: nest tree, nest-tree area (0.04 ha circle centered at nest tree), and nest stand (homogeneous forest stand surrounding nest). Nest stands ranged from 0.4 ha to 13.0 ha (x = 2.7 ha, SE = 0.4). We compared habitat characteristics at nest-sites to those measured at random sites. The mean diameter at breast height (dbh) of nest trees was larger (P < 0.001) than the mean dbh of trees in either the nest-tree area or the nest stand. Nest trees also were taller (P < 0.001) and had greater dbh (P < 0.001) than trees in random stands. Slopes at goshawk nests were more (P = 0.04) moderate (x = 11%, SE 1.1, range 1 to 34%) compared to those available. Aspects at goshawk nests were similar (P = 0.61) to those available. The tree density in goshawk nest stands was lower (P = 0.045) than random stands. However, nest stands had a higher (P < 0.001) density of large trees compared to random stands. Trees in nest stands also were taller (P < 0.001) with greater (P = 0.006) heights to live canopy compared to trees in random stands. The mean density of small trees at nest stands was less than (P = 0.001) one-half those present in random stands. Nest stands were not old-growth in the classic sense of being multi-storied stands with large diameter trees, high canopy closure, and abundant woody debris. Rather, nest stands were in even-aged, single-storied, mature forest stands with high canopy closure (x = 65%, SE 1.4) and clear forest floors. We recommend changes in procedures for identifying mature and old-growth lodgepole pine forests and describe silvicultural methods for creating goshawk nest stands.