Triste for Tat

The promiscuous Red-Winged Blackbird. (Courtesy Kirk M. Rogers)

For many winter-weary New Englanders, the first jubilant call of the red-winged blackbird is a sure sign that spring is finally here.

The males arrive first, scope out and claim the best nesting sites and vigorously defend them from interlopers. The guys that win the best territories are stronger and make better mates. When the females arrive, they critically examine the real estate, select the best territory for nest sites and food availability, and accept the resident male as their mate.

A female lets a male know she’s chosen his territory by building a nest and returning his call. But they aren’t the only blissful pair in his territory—the male may have as many as 14 other females nesting on his property. It appears that the roughest, toughest guys get all the chicks.

But that’s not the whole story. As many as 99 percent of female blackbirds mate with neighboring territorial males, or with roving bachelors that have no real estate of their own.

Scientists aren’t sure why, but in some places females don’t seek outside partners. While in others, females actively seek affairs. These cheaters actually produce more fledglings than faithful mates. Why would cheating females be more successful nesters? The most eligible males just might not have enough room for another girl in their territory. So female red-winged blackbirds looking for the very best genes will move in with neighboring guys and encourage secret trysts.