House Wrens are complicated, mysterious cheaters

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I got my start in ornithology studying the love lives of House Wrens. House Wrens pair up to raise their babies in a manner compellingly analogous to the human “nuclear family;” but, like most birds, both partners also often “cheat” on each other (i.e., copulate with other birds). This means that the male wren may have chicks in other nests besides his own, and he may end up caring for chicks that are not biologically related to him. (Note: edited. The original version of this sentence had a mistake.)

This sets up a number of interesting questions, such as: why cheat on your partner? Are the chicks sired by outside birds somehow better? Do males know when they are caring for chicks who aren’t their own? The answer to the latter question seems pretty clear (no, the males do not know), but the former two are more challenging.

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What we know about one nest

On July 1, 2013, we caught a female junco who we banded MABY.

MABY

MABY

An already-banded male, ARKM, seemed very upset about this. Sometimes juncos do hang around when we band their mates—it’s rather sweet to see them reunite when the banded birds are released—but ARKM’s behavior seemed different to me, so after we released MABY, I lurked behind a tree and watched.

Sure enough, ARKM went down to the ground: he had a nest.

ARKM and MABY's nest, just under the rock.

ARKM and MABY’s nest, just under the rock.

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