ScienceShot: Why Some Male Marsh Harriers Dress in Drag

All's fair in love and war, even among marsh harriers, a bird of prey found in western France. Some male harriers are colored almost exactly like females, with mainly brown plumage and white heads and shoulders, instead of the overall gray of adult males. It's not because they are immature, as is the case in many bird species, but because they spend their life in drag, a type of permanent mimicry known in only one other species of bird. Since some 40% of males in one population of the raptors "dress" like females, scientists surmised that there must be an advantage. And indeed, true males aren't as aggressive toward these female-mimics, the researchers discovered after setting out decoys in breeding males' territories. Since they don't have to worry about serious fights with their male neighbors, the female-like males can horn in on the breeding males' territories and their mates, the scientists report online today in Biology Letters. Intriguingly, the female-plumage-mimics not only look like females—they even behave like them, too: They attacked the female decoys the scientists set out, while largely ignoring male decoys. They also attacked the decoys of female-mimics as the female-colored male is doing in the photo above.

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