Maggie's Farm

Conventional wisdom says you should put up your bluebird boxes in pairs. The 2 boxes in each pair should be only 10-15 feet apart, while pairs should be set 50-75 feet apart. The reasoning behind this is that tree swallows will move into one box of each pair, then chase off any other tree swallow that attempts to nest within about 20-30 feet. The second box of the pair is within that radius, so it will be left swallow-less and some other species of bird, like bluebirds, can move in.

I hear that some recent studies have contested the above conventional wisdom, but it certainly seems to work on the bluebird boxes at the local nature center. They have about 110 boxes set up in pairs. Every year, one box of every pair has tree swallows, and the other doesn't. The bluebirds, chickadees, house wrens, and other birds that occasionally use that size nestbox never lack for available boxes.