We’ve all observed social contagion in humans: When one person laughs, it’s hard not to laugh too, or if someone screams “Fire!” in a movie theater, everyone stampedes toward the door.

The Adouin’s gull discovered a particularly good beach for breeding in Spain in 1981, and within six years, half the world’s population of the bird was breeding there, climbing all the way to 73 percent by 2006. But foxes discovered the birds. Although the foxes only killed a few adult birds, the population crashed as birds moved elsewhere. In 2017, only three percent of the world population bred at the beach.

In a new study published in PNAS, External Professor and UC Davis professor emeritus Alan Hastings and colleagues analyzed the fluctuating population with a detailed mathematical model and found that it could be explained by the departure of a few individual birds influencing others to leave too, until only a few die-hard patriots of that particular beach remained.

Read the study “Social copying drives a tipping point for nonlinear population collapse” at doi.org/10.1073/pnas.2214055120