INFLUENCE OF FOREST EDGE ON NEST-SITE SELECTION BY TREE SWALLOWS

We examined the influence of forest edge on nest-site selection by Tree Swallows (Tachycineta bicolor) at nest-box grids in uniform habitats. Tree Swallows occupied nest sites at distances of 3-100 m from forest edge, while House Wrens (Troglodytes aedon) and most Eastern Bluebirds (Sialia sialis) used boxes within 30 m of forest edge. Mean distance to forest edge for the distribution of nest boxes used by Tree Swallows was greater than those means for Eastern Bluebirds and House Wrens, but mean distances to forest edge for next boxes occupied by the latter two species were not different. Partial correlation analysis showed that settlement dates at nest boxes by single Tree Swallows (often known to be males), and dates of pair formation, were correlated negatively with distance to forest edge (i.e., Tree Swallows settled first at nest boxes that were farthest from forest edge). Also, when a pair of Tree Swallows had a choice of more than one nest box in which to breed (i.e., their territory included more than one nest box), they selected most frequently the nest box farthest from forest edge. Whereas predation by raccoons (Procyon lotor) and black rat snakes (Elaphe obsoleta) at Tree Swallow nest boxes occurred at distances from forest edge up to 80 m, House Wrens destroyed eggs and usurped nest boxes from Tree Swallows only within 20 m of forest edge. Further, although Eastern Bluebirds did not usurp nest boxes from Tree Swallows, both species are known to compete aggressively for boxes. Therefore, Tree Swallows may select nest sites farther from forest edge to avoid the costs of aggression or nest destruction that may be incurred during interactions with competitors, especially House Wrens.