Relationships of Surrounding Riparian Habitat to Nest-Box Use and Reproductive Outcome in House Wrens

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Abstract
I assessed relationships among habitat structure, nest-site selection, and reproductive outcome of House Wrens (Troglodytes aedon) by establishing three nest-box grids in riparian woodlands in southeastern Wyoming. Over a 3-year period, 37% of the boxes contained House Wren nests; 20% contained unused nests built by male House Wrens; and 42% were never used by wrens. Direct discriminant analyses separated three box-use groups (unused, 1-year use, 2- to 3-year use) and three nesting outcome possibilities (failure all years, 1-year success, 2- to 3-year success) along gradients of habitat cover and foliage density. Compared with unused boxes, those selected repeatedly by House Wrens were located in habitats with sparser understories. Similarly, wrens were more likely to fledge offspring from boxes chosen in sparsely foliated habitats. I conclude that characteristics of the surrounding habitat influenced wren reproductive outcome and suggest that boxes in open habitats were actively selected based on their higher probability of success. Predation was the major cause of nesting failure. By nesting in open habitats, House wrens may be more adept at detecting and deflecting cavity-nest intruders before nests are discovered and destroyed.