Early spring due to warming climate declining birds' population, study finds

Birds produced fewer young if they started breeding too early or late into the season

Published - July 04, 2023 03:14 pm IST

Warming climate is making birds produce fewer offspring by advancing spring-like weather, hence the birds’ breeding season, and the birds not being ready to reproduce.

Warming climate is making birds produce fewer offspring by advancing spring-like weather, hence the birds’ breeding season, and the birds not being ready to reproduce. | Photo Credit: B. Jothi Ramalingam / The Hindu

Birds are producing fewer offspring as their readiness to breed is at odds with the onset of spring, the breeding season of songbirds, which is arriving earlier due to a warming climate, says new research.

Suggesting that breeding productivity may decrease by about 12% for the average songbird species, the research said that the mismatch between an early spring onset and the birds' readiness to breed is likely to get worse as the world warms.

Birds produced fewer young if they started breeding too early or late into the season, the research led by scientists at University of California Los Angeles (UCLA) and Michigan State University, US, found.

With climate change resulting in earlier spring-like weather, the birds have been unable to keep pace, the researchers said in their study published in the journal Proceedings of the National Academy of Sciences (PNAS).

"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 the study's first author, Casey Youngflesh, currently a postdoctoral fellow at Michigan State.

For birds, timing matters when it comes to raising their offspring. The harsh weather while breeding too early or late could harm their eggs or newborns.

What also matters is timing regarding food sources - looking for food before or after they're naturally available could mean the birds do not have the resources to keep their young alive.

In this study, the researchers calculated the timing of breeding and the number of young produced for 41 migratory and resident bird species at 179 sites near forested areas throughout North America between 2001 and 2018, using data from a large-scale collaborative bird banding program.

Then, using satellite imaging, they determined when vegetation emerged around each site.

The scientists found that, overall, for every four days earlier that leaves appeared on trees, hinting spring onset, species bred only about one day earlier.

They found that the majority of birds were adversely affected by variations in the start of spring, even as some non-migratory bird species - the northern cardinal, Bewick's wren and wrentit among them - were found countering the trend.

However, the scientists said they were exceptions to the rule, because most non-migratory species couldn't keep up with earlier spring onsets.

For migratory species, earlier spring onset conditions meant even shorter breeding timeframes as after arriving at their breeding sites, birds need time to establish territories and prepare physiologically for egg-laying and offspring-rearing, before they start breeding.

The authors stressed that conservation strategies should address bird species' responses to climate-driven shifts.

"North America has lost nearly a third of its bird populations since the 1970s," said Morgan Tingley, a UCLA associate professor of ecology and evolutionary biology and the study's senior author.

"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," said Tingley.

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