Baltimore Oriole Photo by somebody

Bluebird Cartoon

illustration comparing a situation when a bluebird will not let a chickadee nest in a nearby nest box with a large entrance hole, to a situation where the bluebird is allowing the chickadee to nest in a nest box with a small entrance hole.

When paired boxes have identical entrance hole sizes, small birds like chickadees may be excluded from nest sites

Cornell Lab of Ornithology

Cornell Lab of Ornithology