Climate change could be making birds shrink in size, study finds

05 Décembre, 2019, 02:08 | Auteur: Therese Cote

Researchers are now examining the same data set to better understand why the wing length of so many species increased over the last several decades.

A study published on Wednesday involving 70,716 birds killed from 1978 through 2016 in such collisions in the third-largest US city found that their average body sizes steadily declined over that time, though their wingspans increased.

Birds across species have slowly been shrinking, The Washington Post reports.

New analysis of a robust bird-size data set suggests migrating songbirds are getting smaller as climate change continues to raise global temperatures.

Every night during the spring and autumn migration seasons, nocturnal birds making their way through Chicago run into the windows of big buildings.

"Migration is an incredibly taxing thing they do", Mr Weeks said, explaining that the smaller body size means less energy available for the birds to complete their long journeys. Numerous birds hit the hulking glass McCormick Place, North America's largest convention center.

"Wing length is an incredibly ecologically-important trait in birds", Brian Weeks, lead study author and an assistant professor of environmental science at University of MI, told UPI.

Migratory songbirds in IL are no exception to Bergmann's rule, which posits specimens representing that same species tend to be smaller in warmer climates and bigger in colder climates.

Willard began collecting the dead birds after someone casually mentioned they were hitting windows, including at McCormick Place, North America's largest convention center, which is just a mile away from the Field Museum.

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"Periods of rapid warming are followed really closely by periods of decline in body size, and vice versa", Weeks said. "I found a couple dead birds and I brought them back to the museum-I've always wondered if there had been no birds that morning whether I would have ever bothered to go back".

In birds, tarsus length is considered the most precise single measure of within-species variation in body size. The average body mass fell by 2.6%.

For the latest study, David Willard, a Field Museum ornithologist, measured the length of the leg, the wing, the beak and the weight of each bird carcass kept at the museum. Temperatures at the birds' summer breeding grounds north of Chicago increased roughly 1 degree Celsius (1.8 degrees Fahrenheit) over the course of the study.

The consistency of the body-size declines reported suggests such changes should be added to the list of challenges facing wildlife in a rapidly warming world.

"It's clear that there's a third component-changes in body size and shape-that's probably going to interact with changes in range and changes in timing to determine how effectively a species can respond to climate change".

As the birds' bodies got smaller, their wings gradually got longer, the scientists said in a paper published Wednesday in the journal Ecology Letters. The number of birds we get each day is highly variable depending on whether it's a big day of migration.

Several species of sparrow, warbler and thrush make up the majority of the dataset - with thousands of individuals of each species documented as lethal collisions. "The results of this study highlight how essential long-term data sets are for identifying and analyzing trends caused by changes in our environment", says Willard, a collections manager emeritus at the Field Museum and one of the authors of a new study in Ecology Letters presenting these findings, along with lead author Brian Weeks and senior author Ben Winger from the University of MI.

The authors say the study is the largest of its kind and that the findings are important to understanding how animals will adapt to climate change.



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