Female common merganser. Photographed Dec 28, 2025, from Olympic Discovery Trail
From Cornell Lab of Ornithology: Common Mergansers usually nest in natural tree cavities or holes carved out by large woodpeckers. Sometimes mergansers take up residence in nest boxes, provided the entrance hole is large enough. On occasion they use rock crevices, holes in the ground, hollow logs, old buildings, and chimneys.
Wow. Am I alone in being amazed to learn these large ducks can nest in holes carved out by woodpeckers and also sometimes wedge themselves into chimneys?
Sorry, but there’s nothing common about these birds.
Tracy Abell 
Well, if you’ve ever seen a piliated woodpecker going at it, you’ll understand why the hole can be quite large. The effort that they put into getting that next elusive insect a few millimeters deeper inside the decaying tree can add up. I have a piliated woodpecker that shows up behind our house as he/she makes the rounds.
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Oh, lucky you, Jasper! I love piliated woodpeckers and have only seen one. They do make large holes. Still, it boggles my mind to think of a duck wedging itself into one. 🙂
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The duck might be using the logic of, “If I have a very hard time getting into this crevice, then a predator might not bother trying to attack me.”
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