AVIAN RESPONSE TO NEST BOX ADDITION IN 2 FORESTS OF THE COLORADO FRONT RANGE

Numbers of birds on 54 circular plots (50-m radius) were counted in tw o Colorado forest sites for 2 yr, then four artificial nest boxes were added to each of 27 of the plots, and counts continued for 2 more yr. Combined abundances of eight box-using species increased more than th reefold on experimental plots compared to unmanipulated control plots, apparently as a result of the box additions. Common cavity-nesting sp ecies that responded most strongly to nest box additions included the Mountain Chickadee (Parus gambeli), Pygmy Nuthatch (Sitta pygmaea) and House Wren (Troglodytes aedon). Combined abundances of open-nesting s pecies did not change on experimental versus control plots during the experiment. Results of this study suggest that secondary cavity-nester s were limited by the quantity or quality of available nest sites, but that increased numbers of cavity-nesting species had no affect on abu ndances of open-nesting species.