| The U.S. Forest Service collected nesting data on bird use of aspen, conifer and mixed stands in the Routt and Medicine Bow National Forests between 1987 and 1989. Aspen, the most abundant tree in North America, is an important nest substrate for many bird species. I evaluated this habitat and found active nest sites of 39 species of small nongame birds on 15 undisturbed study plots, 9 in aspen, 3 in conifer, and 3 in mixed stands. Nest site parameters, nest success, adult behavior, and stand-level parameters were measured. The nesting period (average time from laying to fledging) survival rates of the 8 most common species in order of sample sizes in aspen stands (years pooled) were house wren=0.27, American robin=0.79, tree swallow=0.51, warbling vireo=0.47, western wood-pewee=0.27, northern flicker=0.16, red-naped sapsucker=0.09, dark-eyed junco=0.80. The data were also pooled into nesting and life-history guilds. Nest success was compared within a habitat between species and guilds and between habitats for species and guilds. Dark-eyed juncos were the only common birds to use all 3 habitat types. Nest site use patterns were compared between species and guilds using univariate tests. Binary logistic regression models of nest success (success=at least one nestling) using nest site and stand-level parameters as explanatory variables. None of the species or guilds had a stand-level model converge with more than one significant explanatory variable. Only tree swallows, small migrants and residents, and secondary cavity nesters had significant models using nest site variables. Relationships with nest success and parameters thought to greatly influence nest predation were examined with univariate tests. |
