[Tweeters] Wood Duck Aggression

Lee Rentz lee at leerentz.com
Sun Apr 14 21:38:20 PDT 2013

As of tonight, all three of our duck nest boxes have incubating females: one is a Wood Duck with approximately 18 eggs; the second is a Hooded Merganser with an unknown number of eggs; and the third is a Wood Duck incubating eggs from both species (they often do this, in our long experience watching these two very different duck species that have similar nesting habitats, nesting habits, and incubation time. Nature seems to have designed both species to benefit from this arrangement).

Last night there was a fascinating event that we had never seen before. A swallow (not sure if Tree or Violet-green) entered the nest box at twilight, when there was not a duck inside (the all night incubation started tonight), to roost for the night. I checked on it periodically through the night, watching our video feed, and found that the swallow had changed its location frequently within the box, but always lay on the wood chips at the bottom.

In the morning, a Wood Duck arrived shortly after daybreak, stuck its head inside the box and seemed surprised to see the swallow. After a few seconds, it entered the box and flopped down atop the swallow. After a bit of squirming for perhaps 20 seconds, the duck left, but the swallow remained.

Shortly after that, a female Wood Duck (not sure if it was the same one) entered the box, settled down, then repeatedly pecked at the swallow, at one point grabbing it with its bill and shaking the swallow a bit. The swallow died, and the duck covered it up after laying another egg.

What I found interesting was the swallow's behavior. It seemed sick, because it did not resist the duck's attack. But then I recalled that some birds–including swallows–enter a state of torpor at night and can take 20 minutes to fully awaken. Could it have been a state of torpor that prevented the swallow from fleeing the box in the face of danger? Any thoughts in Tweeterdom?

Lee Rentz
lee at leerentz.com
Shelton, WA

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