Michigan's two-track roads and rivers: edge effects for Ovenbirds and Red-eyed Vireos?

Abstract

Declines in neotropical songbird populations have often been attributed to fragmentation, especially the related effects of decreased patch size and increased amount of exposed edge. Negative edge effects have been proposed to be the result of a variety of causes such as increased nest predation and parasitism and decreased prey availability. Studies on edge effects have been largely inconclusive and few generalizations have been made about how edges and edge effects should be defined. Little is known about the degree to which roads, especially narrow un-maintained roads, have corresponding edge effects to fragmentation-sensitive bird species. This study used mist-netting to look at the separate and combined effects of two-track road edges and river edges on ovenbirds (Seiurus aurocapillus) and red-eyed vireos (Vireo olivaceus) in Northern Michigan. Negative edge effects within 50 meters of two-tracks were found for red-eyed vireos but not ovenbirds (p=<.05 and .9, respectively). However the results suggest that ovenbirds may actually experience edge effects for a minimum of 100 meters; further studies should evaluate greater distances from two-track edges. Red-eyed vireo distributions were not influenced by proximity to rivers (p=.9), but female and hatch-year ovenbirds were caught most frequently at sites with riparian habitat (p=<.05) although, within those sites, only hatch -year ovenbirds were caught with greater frequency at nets within 50 meters of the river (p=<.05). This distribution suggests that riparian habitat may counteract two-track edge effects. To be most effective, conservation efforts in Northern Lower Michigan and similar areas should focus on, but not be limited to habitats with river systems.