Viktoriia Radchuk, an evolutionary ecologist at Berlin's Leibniz Institute for Zoo and Wildlife Research, wanted to know how animals were responding to climate change.
So she scoured the results of more than 10,000 animal studies — on species from frogs to snakes, from insects to birds to mammals — looking for information on how changing environments were affecting animal behavior. Based on the available data, she decided to focus on birds in the Northern Hemisphere.
As detailed in a new paper in Nature Communications, Radchuk and her co-authors found that many birds are adapting to climate change — but probably not fast enough. "Which means, on average, these species are at risk of extinction," she says.
The data focused on common and abundant bird species, such as tits, song sparrows and magpies (which are also the most well documented in studies). They showed that some bird populations are breeding, laying eggs and migrating earlier, which makes them better prepared for earlier onsets of spring — a significant effect of climate change.
Radchuk explains that when temperatures warm, plants flower earlier, and insects also develop earlier.
"For many birds, insects are their food source, which means that birds [should] time their egg laying to correspond to the peak of prey abundance," she says, so their chicks have lots of food. Some birds have been shifting to earlier dates.
"We've known for a long time that global climate change is happening. We've known for a long time that animals are changing in response to this. But what we really haven't known is how well the animals are keeping up with the selection," says Melissa Bowlin, an ecologist at the University of Michigan-Dearborn who was not involved with the study.
The paper, which is largely based on studies from the past 30 years, comes to a stark conclusion: "The temperature is changing so fast that evolution isn't able to keep up," Bowlin says.
The abundance of the species in the studies is evidence that they are already better able to adapt to changing environments, says Radchuk. "So we would expect that the species that are rare and in danger already — from habitat fragmentation or invasive species or any other environmental change — would be even more sensitive to climate change."
Bridget Stutchbury, a field biologist and ornithologist at York University in Toronto, is hopeful because birds have shown resilience in the past.
"At least for birds, many of the studies are done on species that are relatively short-lived, and they reproduce very easily," she says. "Those traits allow them to adapt and respond quickly to changes."
Stutchbury points to the bald eagle, whose U.S. population in the lower 48 states declined to 417 pairs in the 1960s but then rebounded to nearly 10,000 in the mid-2000s, after the federal government banned DDT and helped protect their habitat. "They can recover very quickly if we can put the environment back on track for them," she says.