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Cooperative Breeding in the Bird World

Dear Bird Folks,

In one of your recent Facebook postings there was a photo of two male bluebirds on a single nest box. You claimed that both males, and a female, were attending the baby birds. I hate to question you, but isn’t it possible that one of the males in the photo just happened to be sitting on the box when the photo was taken and had nothing to do with the babies?

– Frank, Chatham, MA


Yo, doubting Thomas,

Or in your case, doubting Frank. I can’t believe you are questioning me. When have I ever written anything that wasn’t 100% accurate? Oh, right. I forgot about last month’s Gull Shark story. Okay, that’s one. Actually, when I received that photo I was also skeptical, so I wrote to the photographer (Sandra from Dennis, MA). Sandra confirmed that she witnessed both males, and a female, attending and feeding baby birds. How about that? Here we have an actual case of ménage à bluebird. But that’s not the most amazing part of the story. The astonishing thing is that I posted something on Facebook. Me! I still can’t figure out which button opens the trunk of my car, but I somehow managed to post something on Facebook. It’s shocking.

What is going on in the nest box in Dennis is known as “cooperative breeding.” I know cooperative breeding sounds like something that was forced onto the people in the old Soviet Union, but it’s actually a natural occurrence. Over 300 different bird species participate in some kind of cooperative breeding, which is when one or more extra birds help raise some other bird’s babies. In the avian world these extra birds are known as “helpers.” (In the human world they are known as “mothers-in-law.”)

The concept of cooperative breeding has intrigued researchers for years. After all, why would a bird want to forgo its own breeding season and instead help raise somebody else’s kids? Aren’t birds programmed to do whatever it takes to pass their genes on to another generation? Why would birds suddenly sign up to be an au pair? What’s in it for them, besides getting paid under the table?

It’s a little tricky, but for the most part helpers are young birds that, for a variety of reasons, aren’t able to breed at that particular point in time. But the helpers don’t volunteer their services to just any random birds; they typically give their assistance to their own mothers. By doing this, the helper’s genes are also passed on, at least in part. Another reason why some birds assist their parents is because in certain locations good breeding territories are hard to find. By remaining with their parents the helpers will have first dibs on the territory should something happen to the parents. You know, like the human child whose only goal in life is to outlive the parents, so he or she (but most likely, he) will end up with the family house.

One of the most noted cooperative breeders is the Florida Scrub Jay. As their name suggests, Florida Scrub Jays are restricted to scrubby woodlands in, of all places, Florida. Holding a prime territory is key to their breeding success. Any jay that attempts to breed in a non-prime territory has little chance of attracting a mate. So instead of wasting everybody’s time, the loser birds simply stay home and help their parents. Do helpers actually increase the chance of nesting success? Yes, in this case, it appears they do. Helpers are beneficial for two reasons. Not only do they provide supplementary food for the nestlings, which in turn means less stress for parents, but the extra eyes provide additional predator detection. And if a predator is detected, the helper birds will readily join in the screaming. Yes, screaming. Don’t forget these are jays and no bird enjoys screaming more than a jay.

What is interesting about the bluebirds in the photo (Remember the photo?) is that they are Eastern Bluebirds. Cooperative breeding is rare with Eastern Bluebirds. (Conversely, Western Bluebirds regularly have helpers, but we aren’t talking about them right now.) Occasionally, an Eastern Bluebird couple will end up with a helper, but these helpers are almost always juvenile bluebirds from an earlier brood. But unlike the scrub jays, these young bluebirds aren’t much help at all. Oh, they want to help, but they mostly end up being counterproductive. They are like the company you’ve invited over for dinner who try to assist with the cooking, but just get in the way. You finally have to tell them to go sit down and eat the clam dip.

Now comes the head scratcher part, Frank. The bluebirds in Sandra’s photo are all adults. There is no obvious juvenile. So what gives? Something weird is going on in Dennis, I mean weirder than usual. My guess is that the extra male in this ménage à bluebird is a late hatchling from last year and he wasn’t able to find a nest site of his own. Remember, unlike robins and cardinals, bluebirds can’t simply build a nest in the nearest bush. Their nesting options are limited to old woodpecker holes or birdhouses. If they can’t find a hole, they can’t nest. Since one of these male birds couldn’t raise a family of his own, he decided to do the next best thing and help his parents be successful. It will be interesting to know if the bluebird parents appreciated his help or if he just got in their way. I’ll have to send Sandra a note to see if she can smell clam dip. If she does, we will have our answer.