Birds Are Laying Eggs Earlier Likely Due to Climate Change

It’s an annual harbinger of spring: Birds singing, building nests, and laying eggs. But the timetable has been gradually changing. A new study finds that many bird species are building their nests and laying eggs nearly a month earlier than they did a century ago. Researchers compared bird egg information from museum collections with recent bird behavior observations and found that about one-third of the bird species that nest in Chicago have moved their egg-laying to an average of about 25 day

In addition to that set of data, the researchers had information collected on eggs from 1990 to 2015 by Bill Strausberger, a research associate at the Field who studied cowbirds, and from Whelan, who had amassed modern songbird nesting data. They filled in any gaps in data by creating a statistical nesting model for those missing years. Then they compared the century-old egg information to the contemporary nesting details. They found that about one-third of the 72 bird species for which they had old and new data were nesting earlier in the year. The actual extent varied a bit among species.