Birds raise fewer young when spring arrives earlier in a warming world
Scientists finds conservation strategies should address avian responses
to climate-driven shifts

Date:
July 3, 2023
Source:
University of California - Los Angeles
Summary:
A new study of North American songbirds finds that birds can't
keep up with the earlier arrival of spring caused by climate
change. As a result, they're raising fewer young. By the end of
the 21st century, climate change will cause springlike weather to
begin 25 days earlier, but birds will only breed about seven days
earlier. That change could lead to an average reduction of 12%
in breeding productivity for songbird species.


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FULL STORY ========================================================================== Rising global temperatures are making it harder for birds to know when
it's spring and time to breed according to a new study published in
Proceedings of the National Academy of Sciences.

A large collaboration led by scientists at UCLA and Michigan State
University has found that birds produce fewer young if they start breeding
too early or late in the season. With climate change resulting in earlier springlike weather, the researchers report, birds have been unable to
keep pace.

And, the authors write, the mismatch between the start of spring
and birds' readiness to reproduce is likely to become worse as the
world warms, which could have large-scale consequences that would be catastrophic for many bird populations. Birds' breeding seasons begin
whenever the first green plants and flowers appear, which is happening
earlier and earlier as the climate warms.

"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, who led the research
as a postdoctoral researcher at UCLA and is now a postdoctoral fellow
at Michigan State. "Our results suggest that breeding productivity may
decrease about 12% for the average songbird species." The authors stress
that conservation strategies should address bird species' responses to climate-driven shifts.

Determining if the earlier springs will pose problems for migratory
birds has been a major goal of biologists for decades.

"For nearly 30 years, scientists have hypothesized that animals
could become mismatched from plants as springs begin earlier," said
Morgan Tingley, a UCLA associate professor of ecology and evolutionary
biology and the study's senior author. "While there have been a few very
good case studies of this phenomenon, it has remained a major mystery
whether advancing springs will pose a general problem for the majority
of species." When it comes to raising their young, timing matters for
birds. If they breed too early or too late, harsh weather could harm
their eggs or newborns. But timing relative to food sources matters too:
If birds are looking for food before or after its natural availability,
they might not have the resources to keep their young alive.

"Critically, we found evidence for impacts on bird reproduction of both
the absolute and the relative timing of birds," Tingley said.

Using data from a large-scale collaborative bird banding program run
by the Institute for Bird Populations, 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.

Then, the authors used satellite imaging to determine when vegetation
emerged around each site. They found that each species had an optimal time
to breed, and that the number of young produced decreased when spring
arrived very early, or when breeding occurred early or late relative to
when plants emerged.

While the majority of birds were adversely affected by variations in the
start of spring, several species -- the northern cardinal, Bewick's wren
and wrentit among them -- countered the trend, demonstrating improved
breeding productivity when spring began earlier. Those species are mostly non-migratory species that can respond more quickly to the emergence of
spring plants that signal the start of the breeding season.

By breeding earlier and without the time constraints imposed by migration,
the study noted, non-migratory species may also be able to reproduce
more than once per season.

But those species were the exceptions to the rule. Even most non-migratory species couldn't keep up with earlier spring arrivals. Overall, for every
four days earlier that leaves appeared on trees, species bred only about
one day earlier.

For migratory species, that discrepancy means that the time between
when they arrive at their breeding sites and breeding itself is likely
to get shorter as springlike conditions begin earlier. Birds need time
to establish territories and prepare physiologically for egg-laying and
rearing their young, so that change could cause even greater disturbances
to reproduction.

"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." The study received primary funding from
the National Science Foundation and was supported by researchers from
the University of Florida; Pennsylvania State University; University of
North Carolina, Chapel Hill; and the Institute for Bird Populations.

* RELATED_TOPICS
o Plants_&_Animals
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# Rainforests # Environmental_Awareness # Climate #
Environmental_Policy
* RELATED_TERMS
o Global_warming_controversy
o IPCC_Report_on_Climate_Change_-_2007 o
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o Kyoto_Protocol o Attribution_of_recent_climate_change o
Weather o Climate

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Story Source: Materials provided by
University_of_California_-_Los_Angeles. Original written by Holly
Ober. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Casey Youngflesh, Graham A. Montgomery, James F. Saracco, David
A. W.

Miller, Robert P. Guralnick, Allen H. Hurlbert, Rodney B. Siegel,
Raphael LaFrance, Morgan W. Tingley. Demographic consequences of
phenological asynchrony for North American songbirds. Proceedings
of the National Academy of Sciences, 2023; 120 (28) DOI:
10.1073/pnas.2221961120 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/07/230703160005.htm

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