A wasp nest and a dead bluebird in a nest box

wasps
Western Bluebirds guard a nest box. Photo by Steven Grogger

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In the column “Since You Asked” in every issue of BirdWatching, Contributing Editor Julie Craves answers readers’ questions about birds and bird behavior. Here is a question from our September/October 2018 issue. 

A European paper wasp grates wood fibers to be used building a nest. Photo by pjt56 (Wikimedia Commons)

I just repaired some bluebird houses and found an abandoned paper wasp nest and a dead bluebird in one. Did the wasps sting the bird to death? The bird nest was complete, so I assume the birds were in the house before the wasps arrived. If that’s the case, why didn’t the bird eat the wasps before they became too numerous? — Dan Innamorato, via the Internet

Wasps typically will not attempt to build a nest in a box already occupied by bluebirds, although it depends on the species of wasp and probably the availability of appropriate nesting sites for the insects. A wide variety of North American birds have been known to eat bees and wasps, but most reports I have located involve smaller and more docile species of stinging insects than the fairly aggressive European paper wasp, which commonly uses nest boxes. A bluebird might be more apt to abandon a box invaded by wasps rather than try to eat its way out of the situation.

Similarly, bluebirds would not try to nest in a box that already contained wasps. Without a nest to defend, the wasps would probably not attempt to sting the bluebird. Although I’ve not found any data regarding how many wasp stings it would take to kill a bird, the stings would have to penetrate the feathers, perhaps requiring multiple attempts. It seems improbable that wasps could kill a healthy adult bluebird that could simply flee the scene.

It’s hard to say what the sequence of events might have been in this situation. I agree the bluebirds were the first occupants. The dead bluebird may have been the nest owner and died before eggs were even laid. Or the bird could have died in the box after it was used. Parasites, starvation, or hypothermia are all causes of adult bluebird deaths. I think it’s most likely that at some point after that, the wasps found the box and built a nest.

For tips on how to prevent wasps from building nests in nest boxes, see this post from 2016.

 

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Julie Craves

Julie Craves

Julie Craves is an ecologist and the retired director of the Rouge River Bird Observatory in Dearborn, Michigan. She answers readers’ questions about birds in her column “Since You Asked” in every issue of BirdWatching. A tireless researcher and bird bander with a keen interest in the stopover ecology of migrant birds, she is also a personable writer with a gift for making everything she writes readable and entertaining. Her first article in Birder’s World (now BirdWatching), “Forest Fire-tail,” a profile of the American Redstart, appeared in June 1994. Send a question to Julie. Read her blog at http://net-results.blogspot.com.

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