I've heard they parasitize Prothonotary Warblers, which are
cavity nesters.
>
So that makes me ask: is it the case that cowbirds parasitize
only open bowl-shaped nests? Do they ever go after cavity
nests? I'm afraid I don't know much about them.

Bob Mauritsen
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Chris Maack
Anchorage, AK
CMaack at compuserve.com