Study shows which birds might be impacted most by climate change 

Climate is changing faster than most of the world’s birds can adapt.

Casey Youngflesh, an assistant professor in Clemson University’s Department of Biological Sciences, led a study that examined how a bird’s pace of life — the rate at which it grows, develops, reproduces, and how long it lives — is related to environmental conditions and what that reveals about how they might respond to a changing climate.

The study included 7,477 species of birds — essentially all the world’s resident, non-marine birds — and used global climate data from 1950 to 2022.

Youngflesh and his collaborators from Michigan State University found that a key link exists between how much an environment varies over time and how long birds tend to live. Specifically, species tend to live longer in environments that are more variable from year-to-year, a type of bet-hedging strategy that has long been theorized. 

However, these longer-lived species may be at greater risk as well. All else being equal, these species experience greater change per generation that their shorter lived counterparts. Because more generations means faster adaptation potential, these species are more likely to lag behind in their response to climate change.

“One of the key things that varies among different bird species is pace of life. We were specifically interested in the role of the environment  in potentially driving those differences,” Youngflesh said. “Where do we see ‘slow species’? Where do we see ‘fast species’? And why?”

Live fast, die young strategy

Birds with a “fast” pace of life have shorter lifespans and have as many young as they can during that time, something Youngflesh calls a “live fast, die young” strategy. Birds with a “slow” pace of life have longer lifespans and low rates of reproduction. 

“For a ‘slow’ species, if one year is bad, you’re going to live on to reproduce another year —you’re waiting it out. If you’re a bird that lives 30 years, you could handle a couple of bad years,” he said. “But if you’re a ‘fast’ species and there are several bad years in a row, that might be catastrophic. They may not get an opportunity to breed and raise their young.”

These results have important implications for understanding how species are likely to respond  to climate change. 

While organisms with a slower pace of life (longer lifepans) are expected to be more robust to environmental variability, these species will tend to adapt to directional change at a slower rate. Fewer generations over a given period means fewer opportunities for selection to operate and thus slower evolutionary adaptation. Similarly, for a species that is used to large fluctuations in temperature year-to-year, a small change in temperature might be less meaningful than to a species that experiences very little fluctuation in temperature over time.

All change is not equal

“A one-degree Celsius change in temperature is not equal in all environments,” Youngflesh said. “We are making the case that we need to contextualize rates of climate change in terms of both the historical variability of environmental systems and species’ pace of life.”

Compare two birds in the study: a sulphur-crested cockatoo, which had the longest generation length of any species in the study at 27.2 years, and the double-barred finch, which had the shortest generation length at 1.4 years.

“There might be 19 generations of double-barred finch for every one generation of sulphur-crested cockatoo,” Youngflesh said. “So, the sulphur-crested cockatoo has fewer opportunities for selection to operate and thus slower evolutionary adaptation, all else being equal. Species experiencing higher rates of environmental change per generation are likely to be those that suffer the greatest consequences of climate change. Concerningly, we found that most species, regardless of their pace of life, are likely experiencing rates of change faster than they are likely able to adapt.”

Youngflesh said the study tells scientists which species might be most susceptible to climate change and could be used to prioritize conservation and management efforts such as habitat restoration or preservation for the most sensitive species.

Detailed findings were published in Ecology Letters in an article titled, “Environmental variability shapes life history of the world’s birds.”