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Century-old museum collection reveals birds nesting earlier

Bird Nesting Study
Posted at 11:21 AM, Apr 08, 2022

CHICAGO — It’s springtime, and the birds are chirping as they begin to build their nests.

Researchers say the hands-on clock is turning back, though it happens like clockwork each year. Many species of birds are nesting and laying eggs much earlier than a century ago.

Locked inside a 650 square-foot vault at the field museum in Chicago is a treasure trove of potential ecological data.

Everything is organized by taxonomy. Drawers line the walls containing 21,000 sets of eggs or clutches - how many eggs an individual female will lay at a time. In total, the archive contains more than 300,000 eggshells.

“We've got eggs of a whole bunch of different species of birds,” said John Bates, an evolutionary biologist and curator of birds at the Field Museum of Natural History in Chicago. “The eggs around you here were collected from the 1870s to about the 1920s,” he said.

He’s also the first author of a new study published in the Journal of Animal Ecology that analyzed egg nesting.

By comparing contemporary observations with eggs preserved in museum collections, scientists discovered that a third of their bird species have shifted when they lay eggs.

“Birds in the Chicago region are laying their eggs as much as 25 days earlier than they were 140 years ago,” said Bates.

Researchers found the correlations by overlaying the shifting in nesting with carbon dioxide measurements in the atmosphere over that time - tracking changes in the earth’s climate.

“We always talk about climate change as being so important to humans, but it's really important to biodiversity too,” said Bates.

Twenty-five days may not seem like much – but the impact could be far-reaching. These changes in nesting dates might result in birds competing for food and resources that they never had before.

It could cause a ripple effect across the ecosystem, impacting species' survival.

“This study is just a really small example of some of the things that are clearly happening out there in a very small part of the world.”

The research also highlights the importance of museum collections in providing baseline data for understanding and forecasting future ecological trends.

“We've really only scratched the surface of the kinds of things we can actually look at,” said Bates.

There are about 5 million eggs in all the world's collections.

“The people that collected these eggs in 1897 had no idea about the kind of study that they're being used for now in 2022,” he said.

But egg collecting fell out of favor in the 1920s, and 30’s, which Bates says makes comparisons to modern eggs more challenging.

“There are about 10,800 species of birds, and we actually don't even know what the eggs look like. They're not cataloged anywhere for probably about 30% of those species.”

Besides serving as a warning about climate change, Bates says the study highlights the importance of monitoring birds, insects, and microbes moving forward.

“We're seeing, as a result of the COVID pandemic, what can happen on a global basis with viruses that have been around for millions of years. And so, we can't divorce ourselves from the ecosystems around us,” said Bates.

It’s a reminder that even the smallest changes can have far-reaching impacts.