Birds lay eggs earlier as climate change changes

Of 72 bird species examined around Chicago, about a third are laying their eggs about 25 days earlier than a century ago, the researchers report in the paper published Friday in the Journal of Animal Ecology.

Those affected include the mourning dove, American kestrel and Cooper’s hawk.

So far, scientists have found no clear traits shared by these species, such as size or migratory status, that might explain why they change their schedules.

But “the majority of birds we examined eat insects, and seasonal insect behavior is also affected by climate,” said lead author John Bates, curator of the bird division at the Field Museum in Chicago.

How the life cycles of animals and plants are affected by climate change and seasonal disruptions is a question that “is becoming more and more front and center of people’s minds,” Bates said.

A few degrees of temperature above the long-term average can have a big impact on when insects emerge, when trees grow, when flowers bloom and, according to the new research, when eggs hatch.

Scientists believe these changes could be among many reasons for the steep decline in bird populations since the 1970s, with the United States and Canada losing about a third of their birds – or about 3 billion birds – according to a 2019 study in the journal Science. .

Bates and his colleagues studied more than 1,500 eggshell records held at the Field Museum in Chicago, many of which date back to the period between 1872 and 1920, when egg collecting was a popular pastime. These Victorian egg enthusiasts left detailed handwritten tags showing information such as bird species and date of collection.

The scientists then compared these records with more than 3,000 modern records, along with data describing carbon dioxide levels at nesting dates in time, for their analysis.

The findings echo similar findings from studies over the past few decades in the UK, which also found egg laying occurring earlier, as well as reported changes in the growing season.

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