In the future, Wiens says he’d like to understand what’s happening at these extinction sites in greater detail. While those hot temperatures are most associated with decline, they’re not necessarily the direct cause of species dying out. Instead, it’s probably something more complicated. For example, warmer temperatures might affect the availability of food or lead to an increase in disease, and then those factors lead a population to decline. Also, for the niche shifts, Wiens says it’s unknown whether those are the result of species simply adjusting—say, hanging out in the shade more—or evolving a tolerance to new conditions.