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Birds are laying eggs earlier, a new study shows. Scientists blame the climate crisis

A drawer of eggs in the Field Museum's collection is pictured.

A drawer of eggs in the Field Museum's collection is pictured. (John Bates, Field Museum)



Estimated read time: 2-3 minutes

CHICAGO — Egg-collecting enthusiasts in the late 1880s knew the hobby was crucial for understanding the natural world, but likely never imagined that their research would help scientists more than 100 years later understand how birds are affected by the changing environment.

Using a modern and a Victorian-era collection of egg samples, researchers found that several bird species in the Chicago area nest and lay eggs almost a full month earlier now than they did a century ago, according to a study published Friday in the Journal of Animal Ecology.

The climate crisis is to blame, researchers say.

Of the 72 species documented in their data, a third have been nesting earlier and earlier, the team found. Birds that changed their nesting habits laid eggs around 25 days prematurely, on average.

The team studied egg collections from the Field Museum in Chicago, the Western Foundation of Vertebrate Zoology and the Chicago Academy of Sciences.

Scientists looked at rising temperatures to explain the shift in behavior.

Most of the birds in the data eat insects, and those insects eat plants, so the whole ecosystem is connected, said John Bates, curator of birds at the Field Museum and the study's lead author. And the results of this study are consistent with the patterns in insect and plant communities.

"These stresses haven't necessarily doomed anything to extinction, but they're definitely changing the conditions that all of these organisms are dealing with," said Bates. "And that may have really important ramifications — and anything like that has potentially big implications for humans, too."

Of the two analyzed egg collections, the first included data from around the year 1880 to 1920. The second set ranges from 1990 to 2015, leaving a hearty gap of missing information. The gap, researchers said, was a result of decreased interest in the hobby of egg collecting after 1920.

Mason Fidino, co-author of the paper and quantitative ecologist at Chicago's Lincoln Park Zoo, developed a model to incorporate the approximate change in nesting time during the missing era and overlaid those results with the changes in atmospheric carbon dioxide and temperature.

"What I think (the model) may imply is that there are a lot of factors involved in how birds are responding, even to something like moving their nesting dates forward," Bates said. "We need to do a better job of understanding what factors may be important."

Friday's report is yet another fascinating discovery from the vast trove of bird data held by the Field Museum and other zoology foundations.

Another study found that North American migratory birds appear to be shrinking in response to climate change. And a follow-up showed that birds that have bigger brains, relative to their body size, are not shrinking as much as their smaller-brained counterparts.

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Danya Gainor

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