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

The Field Museum's egg collection is filled with hundreds of eggs with the inner contents blown out. Most were collected about 100 years ago. Each egg is stored along with handwritten notes about what bird it came from and exactly what day it was collected. There's not much to the collection after the 1920s when egg collecting was no longer so popular with scientists or hobbyists. "These early egg people were incredible natural historians, in order to do what they did. You really have to know the birds in order to go out and find the nests and do the collecting," says Bates. "They were very attuned to when the birds were starting to lay, and that leads to, in my opinion, very accurate dates for when the eggs were laid."