Paired Boxes

The biological theory for paired nest boxes is that a nesting species, (e.g. bluebirds) will tolerate another species (e.g. tree swallows) nearby but won't tolerate a pair of its own kind in their territory. The suggested distance between paired nest boxes is one to three fence posts, say 5 to 15 metres. At present the distance apart does not seem significant, and further experimentation would be needed to determine if it is important.

Some monitors deal with paired boxes as follows: They carry around extra nest boxes with them when they monitor. When they notice a pair of tree swallows in the vicinity of an active bluebird nest, they set up a second nest box a fence post or two away. These monitors have had good success using this system with the tree swallows taking over the second nest box immediately, rather than chasing out the bluebirds as had often been the case in previous years. The second nest box could be taken down at the end of the season or left up as desired.

In a few cases, the species taking over the second nest box of the pair will be house sparrows or house wrens, when the species using the first nest box is bluebirds or tree swallows. In certain areas where there is no competition, monitors may find one nest box of a pair empty.

Occasionally monitors have found that bluebirds and tree swallows still fight over paired nest boxes, and several cases have been noted where bluebirds and tree swallows have switched boxes from where they had originally started to nest.

In general, the technique of using paired best boxes appears to give a higher nesting success ratio for both bluebirds and tree swallows.