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Studies of bluebird nestlings have shown that their parents are not always the adults that are attending the nest. Intruding males will often land at a nest box to increase his chances to mate with a resident female, since he knows copulation takes place near her nest site. When a resident male discovers another male in his territory he not only chases him away but copulates with his mate right away. He wants to make sure it is his sperm that is fertilizing his mate. Question often ask, are bluebirds monogamous? Watching the bluebird’s behavioral habits around their nest box surely might indicate so. But then again, once we realizes that extra pair copulations are occurring and the young in the nest box can be from different parents, then all kinds of mixing is going on. I think it’s safe to conclude that bluebirds have been seen as monogamous but at times can be polygamous. I strongly believe bluebird’s pair up more for procreation than for permanent bonding.