Birds of a feather dance together? 

Alex Eben Meyer

View full image

For years, behavioral ecologists believed they understood how the greater sage-grouse, a prairie-dwelling North American bird, chose its mates. After all, when males fought more frequently, they mated more too. The conclusion: Females are attracted to aggression.

But a new study by researchers from Yale and the University of California suggests this may have been a classic case of correlation, not causation—and that females are choosing mates based on other characteristics altogether.

“The same individuals are fighting a lot, and they’re mating a lot. But what that doesn’t tell us is the mechanism. What’s actually going on? How are females making their mating decisions—and how is fighting influencing them, or not?” says lead author Samuel Snow ’21PhD, who conducted the research as a graduate student in Yale’s Department of Ecology and Evolutionary Biology and is now a postdoctoral fellow at the University of British Columbia.  

To find out, researchers analyzed 18 days’ worth of video during mating season. Crucially, they didn’t just track how often males fought and mated. They used a statistical method called a relational event model (adapted from mathematical sociology, where it was developed to understand conversational turn-taking) to understand what else happened before and after mating events. What they found disputed decades of evolutionary theory.

“The females are not paying attention to the fights,” Snow says. “In fact, when the females are there, the males . . . are less likely to start fights, and they end their fight sooner.” 

The researchers found that the females likely choose mates nearly entirely based on male displays during a lek, a type of bird dance.

If not to attract mates, why are the males fighting? It may be about male-male dynamics. Male sage-grouses often interrupt a mating pair mid-copulation; being able to fend off such a competitor—or having the reputation to avoid being targeted—could help secure mating. While important, that doesn’t seem to impress the females. In fact, by fighting instead of flirting, the most aggressive males lost out. 

The findings challenge a century of evolutionary theory. Much early research on sexual selection focused on the sage-grouse and its relatives and claimed females preferred aggressive mates. These ideas shaped theories of human behavior—such as the idea that women are biologically inclined to choose aggressive, competitive men.

As a result, Snow says, the takeaway goes far beyond prairie birds: It’s a call for better research methods to capture complexity, “as opposed,” he says, “to relying on assumptions.”