Aug 18, 2021 | Featured in: Watching Backyard Birds, August 2021

Ask Birdsquatch: One Female and Two Male Western Bluebirds Tending One Nest?

Western bluebirds occasionally have nest helpers. The term for this is cooperative breeding, and it has been well documented.
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Dear Birdsquatch:

This sounds crazy, but I swear there were two daddy bluebirds in my nest box this summer. I saw only one female, but two males regularly brought food to the nestlings. Do you think Mrs. Bluebird had two husbands? Did she lay eggs from both males? The nest was in a hole in a tree in my yard, so I couldn't peek inside. I don't mean to be judgmental, but what the heck was going on in there?

—Elza B., Mill Valley, California

Dear Elza,

Western bluebirds occasionally have nest helpers. The term for this is cooperative breeding, and it has been well documented. Those helpers can be juveniles (usually males) from a previous brood, adult pairs (presumably after their own nest has failed), or adult males.

While western bluebirds do form pair bonds—one female and one male pair up to raise young for one season—genetic testing shows that nearly half of western bluebird nests contain young that are not fathered by the paired male. Mama bluebird gets around, and the young ones in the clutch often have multiple fathers. So, you're right: There probably was hanky-panky going on. But don't feel sorry for Mrs. Bluebird's husband: Western bluebird nests with helpers tend to fledge more chicks than nests without helpers, which is why cooperative breeding is generally a peaceful affair.



About Birdsquatch

Birdsquatch is WBB's tall, hairy, and slightly stinky columnist. He is a bigfoot who has watched birds all his life. His home range is unknown.

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