Give cavity nesters room

Slant-roofed wooden birdboxes are a common sight along farm fences or on posts in a field, but these “bluebird trails” attract more than just the flashy Eastern bluebird (Sialia sialis).

Bluebirds prefer to nest in tree holes but also readily adapt to life in a box, as do several other common species of “cavity nesters” found in our area. Tree swallows (Tachycineta bicolor), black-capped chickadees (Poecile atricapillus) and house wrens (Troglodytes aedon) all will move right into a box. In fact, the wren’s Latin genus name, Troglodytes, translates to “creeper into holes,” a nod to its habit of nesting in virtually any hollow including flower pots, old boots or even coat pockets.

Competition for boxes can be fierce, as the practice of removing dead trees has greatly reduced the availability of natural nesting sites for all cavity nesters. Add to that the pressure from aggressive non-native birds like house sparrows (Passer domesticus) and European starlings (Sturnus vulgaris), and you’ll find that improperly spaced bird boxes in a yard can lead to some pretty intense fights.

Experts recommend spacing bluebird boxes at least 300 feet apart. Birds squabble over boxes closer than that, with aggressive bluebird couples often winning out against the smaller swallows and wrens.

If you do see swallows and bluebirds competing for the same box, one placement strategy is to put two boxes very close together. While this seems counterintuitive, boxes that are no more than 5 to 10 feet apart — or even back-to-back on the same pole—can allow swallows and bluebirds to nest without competition from another pair of the same species.

Nature Note for 8/3/14