Many species of birds are now building nests and laying eggs at a time of year their counterparts from a century ago would have considered outrageously early. Around a third of birds in the Upper Midwest region are now laying their eggs an average of 25 days earlier than they did in the past, according to a new study published in the Journal of Animal Ecology. Researchers examined a collection of more than 50,000 eggs, most of them collected before 1920, held in Chicago’s Field Museum the Washington Post reports. The collection includes extensive information on dates and observations of bird behavior.
Researchers say there is strong correlation between the change in nesting dates and rising carbon dioxide in the atmosphere, the Guardian reports. "It was shocking to find this,” says study lead author John Bates, curator of birds at the Field Museum. "What we can see is clearly pointing in the direction that climate change is having a significant effect on the behavior of birds. It’s another piece of the puzzle we are trying to figure out in terms of impacts." Researchers found that there was a bigger shift in egg-laying dates for migratory species than year-round residents.
Other studies have found that many bird—and insect—populations are in steep decline. Bates says spring weather is becoming more volatile, and that is taking a toll on bird populations. "If you’re a bird and you nest earlier, you put yourself at risk of these cold snaps that can still arrive in spring, which then affects the plants and insects." (Read more birds stories.)