As the world braces for rising global temperatures due to climate change, researchers at UCLA have found that bird populations might be among the most affected by the ever-changing seasons.

A new study of North American songbirds found that birds are struggling to keep up with the earlier arrival of spring, which has been gradually appearing earlier in the calendar year, driven by rising temperatures from global climate change.

As a result of spring arriving earlier than it had previously, songbirds are raising fewer young, UCLA researchers discovered.

Birds typically breed during the spring when the first green plants and flowers begin to appear, researchers said. The change in temperatures is accelerating when those plants appear and making it harder for birds to know when it’s time to begin breeding.

If birds begin breeding too early or too late in the season, they are unable to raise as many young as the weather can damage their eggs or harm their newborn chicks. Changes to the food source could also mean the birds are unable to feed their young.

And those challenges are only going to become greater as the planet continues to heat up and natural seasons begin to shift, researchers theorized.

“By the end of the 21st century, spring is likely to arrive about 25 days earlier, with birds breeding only about 6.75 days earlier,” said Casey Youngflesh, one of the research authors. “Our results suggest that breeding productivity may decrease about 12% for the average songbird species.”

A population decrease of that magnitude would be “catastrophic,” researchers said.

“For nearly 30 years, scientists have hypothesized that animals could become mismatched from plants as springs begin earlier,” said Morgan Tingley, UCLA associate professor of ecology and evolutionary biology. “Critically, we found evidence for impacts on bird reproduction of both the absolute and the relative timing of birds.”

In a collaboration with Michigan State University, researchers analyzed data of a bird banding program by the Institute for Bird Populations. By utilizing satellite imagery and looking at several migratory and “resident bird” species, they found that the total number of young produced measurably decreased when spring arrived very early or when breeding occurred at a different time from when plants began to emerge.

The data was compiled from 2001 to 2018 and included 41 bird species at 179 sites across North America. While some bird species managed to breed and raise their young with some success, the vast majority of the birds studied suffered “adverse effects.”

“Overall, for every four days earlier that leaves appeared on trees, species bred only about one day earlier,” a news release from UCLA reads.

While it doesn’t sound like much, timing is everything for birds to successfully breed and then raise their chicks. Small changes can have massive impacts on the globe and intervention is needed now, rather than later, researchers suggest.

“North America has lost nearly a third of its bird populations since the 1970s,” Tingley said. “While our study demonstrates that the worst impacts of timing mismatch likely won’t occur for several decades yet, we need to focus now on concrete strategies to boost bird populations before climate change takes its toll.”

To read the full study published in Proceedings of the National Academy of Sciences, click here.