LACK OF EDGE EFFECT IN NESTING SUCCESS OF BREEDING BIRDS IN MANAGED FOREST LANDSCAPES

We assessed avian nesting success in two forested landscapes (Chippewa and Superior National Forests) in northern Minnesota. We found 311 ne sts of 33 species in the Chippewa study area and 36 nests of 13 specie s in the Superior study area. Each nest was classified into one of thr ee general habitat types: open (clearcuts with vegetation <2 m high), regenerating aspen (2-8 m high), or forested (trees >8 m high). Mayfie ld nesting success for the most common species in the Chippewa (all of which had open-cup nests) averaged 0.43. Nesting success ranged from 0.18 for the Red-eyed Vireo (Vireo olivaceus) to 0.76 for the Yellow W arbler (Dendroica petechia). Nest predation was the most common mortal ity factor, causing 89.2% of known failures Nest predation among groun d-nesting birds was significantly higher in the Chippewa (55%) than in the Superior (15%) study area (P = 0.038). Nest predation was highest (P = 0.015) in the forest (62.2%) and lowest in open (42.2%) and rege nerating (47.4%) habitat types. Only canopy cover explained difference s in nesting success. which was higher in more open canopies. Distance to forest edge, nest height, and nest concealment had no effect on ne sting success in both forested and open habitats. Brown-headed Cowbird (Molothrus ater) parasitism was low (9.6% in the Chippewa study area) , and parasitized nests were relatively unsuccessful (only 1.7% yielde d cowbird fledglings). Neither cowbirds nor nest parasitism was observ ed in the Superior study area.