Pity the poor bird that wants to sleep in. Lackadaisical male Great Tits are more likely to be cheated on by their partners than those that get up early, scientists reported recently .
The Great Tit is a common Eurasian songbird that’s closely related to North American chickadees. Males usually roost right above the empty nest cavity and wake up before their mates. This allows them to defend their spouses in the pre-dawn hours, when most of the seduction and extra-pair copulations are believed to occur, says lead author Timothy Greives, a biologist at North Dakota State University.
But when the fellas try and get some extra shut-eye, females are apt to cozy up to their neighbors, Greives found. And since the hanky panky is all done covertly, many of the snoozers end up raising chicks that aren’t their own.
Though some birds naturally rise later than others of the same species, Greives and his team of U.S. and German researchers artificially amplified this behavior. For the experiment, they caught nearly three-dozen Great Tits in southern Germany and gave half of them melatonin, a hormone that regulates the body’s circadian rhythm. This caused the tits to sleep in; on average, they spent only an extra 10 minutes in the roost, and still awoke 12 minutes before dawn.
But those few precious minutes were enough time for males to be cuckolded at a significantly higher rate than their earlier-rising rivals. For the most part, the team came to their conclusions by performing paternity tests, though they did observe one female swooping back home before dawn—a likely indicator of illicit action. “It’s not unlike these daytime TV shows, where they do genetic tests and say who’s the daddy,” Greives says. He found that males with the extra melatonin raised an average of 1.9 “illegitimate” chicks, versus 0.7 among un-doped tits. The melatonin males (naively) completed their daddy duties, showing that their ability to raise offspring wasn’t affected.
Grieves and company then turned their attention to the ladies. But when it was the females waking up late, the males didn’t budge. (Greives says that the tit-for-tat behavior—males cheating on sleeping females—could still occur: He might not have seen it due to the study’s small sample size.) Of course, that doesn’t mean that male Great Tits are saints. They may pursue adulterous relationships at other times, and, at the very least, are charmed by any rogue female that comes their way.
Scientists once believed that songbirds were monogamous because both males and females raise the young. With DNA testing becoming more accessible, however, it has become clear that nearly all songbirds—the —engage in extra-pair copulations, Greives says. And as crazy as this lifestyle may be, it serves the purpose of helping birds spread their genes far and wide.
So to all the Great Tit fellas out there: The next time you decide to give your eyes (and sperm) a rest, remember that your bloodline is taking the hit.