Response of avian communities to herbicide-induced vegetation changes

The relationships between avian communities and herbicide modification of vegetation were analyzed on early-growth clear-cuts in western Oregon that had received phenoxy herbicide treatment 1 or 4 years previously. For both 1 and 4 years post-spray, vegetation development was greater in the third height interval (> 3.0 m) on untreated sites. All measures of vegetative diversity on untreated sites exceeded those on treated sites. Overall density and diversity of birds were similar between treated and untreated sites. Several bird species altered their foraging behavior on treated sites, i.e., birds using deciduous trees increased use of shrubs on treated sites. The primary effect of herbicide application was a reduction in the complexity of vegetation, a condition due primarity to the removal of deciduous trees. Small patches of deciduous trees scattered in clear-cuts treated with phenoxy herbicides can maintain an avian community similar to that on untreated sites.