As climate change transforms habitats and natural cycles across the globe, animals will adapt; adaptation is what allowed most species to develop over millions of years. But a new study in Nature Communications comes to a frightening conclusion: Modern plants and animals may not be able to adapt fast enough to survive the pace of human-driven climate change.

Animals generally adapt in one of two ways: either morphologically, such as increasing or decreasing in body mass to better regulate heat, or phenologically, such as adjusting the time they perform life events like mating, reproducing, hibernating, and migrating.

But how are animals adapting to human-driven climate change?

Quantitative ecologist Victoria Radchuk and her colleagues at the Leibniz Institute for Zoo and Wildlife Research evaluated abstracts from over 10,090 scientific studies and drilled down on 71 long-term, high-quality studies. By looking at whether changes in phenological traits and morphological traits were associated with increased offspring, the team assessed animals' adaptation to climate change. Because birds tend to be the easiest animals to track, and because their offspring can also be followed for several generations, avian species dominated the work.

According to their findings, the current pace of change within these species is not enough to keep pace with the expected rate of a changing climate. That’s especially concerning since many of the bird species in the study, including the magpie and great tit, are common birds in their regions. If they can’t keep pace, it’s easy to imagine that less common or geographically isolated species will have an even harder time keeping up. 

“Adaptive responses among rare or endangered species remain to be analyzed,” coauthor Stephanie Kramer-Schadt, also of the Leibniz Institute, says in a statement. “We fear that the forecasts of population persistence for such species of conservation concern will be even more pessimistic.” 

Birds are flexible animals: They can fly to new territory and adjust behavior patterns such as their nesting periods. Because birds have short life spans, adaptive changes can accrue quickly. The impact on long-lived mammals, reptiles, and other classes of animals could also be significant, though few long-term studies exist on how these groups of animals are adapting.

Wildlife ecologist and coauthor Steve Beissinger from the University of California, Berkeley, says that while the situation looks grim, it’s not all negative. “Climate change is definitely, probably, happening at a rate faster than has been experienced in the lifetime of most of these species. That’s the concern,” he says. “But the good news is they are showing flexibility, and we’re producing evidence that their responses are adaptive. The bigger question is whether they can keep it up. That’s a little harder to answer.”

That’s because the types of high-quality long-term studies needed to answer these queries are expensive and difficult to keep going. Beissinger thinks that over the next decade more studies will begin to help scientists understand how well certain species will weather changes in climate. It will also mean teasing out the impacts of other pressures like habitat loss and fragmentation, pollution, competition with invasive species, and other factors that might be changing some of their behavior. 

The main point of the latest study, Beissinger says, is that birds are currently adapting to anthropogenic climate change. That and other recent findings, like the fact that the global heating is unlike any Earth has experienced in 2,000 years, should shift the public debate from whether climate change is happening to how we will respond.  

“The debate’s over,” he says. “You can ask the plants and the animals. They stopped debating and started reproducing earlier, flowering earlier, and returning earlier as the climate has changed. It’s now a question about how fast Homo sapiens can actually respond.”