In a new study, “Climate Change Affects Bird Nesting Phenology: Comparing Contemporary Field and Historical Museum Nesting Records,” published in the Journal of Animal Ecology, scientists were able to determine that about a third of the bird species nesting in Chicago are laying their eggs a month earlier than they did 100 years ago by comparing eggs preserved in museum collections to modern observations. Researchers think the culprit in this shift is climate change.

John Bates, curator of birds at the Field Museum and the study’s lead author, says, “The majority of the birds we looked at eat insects, and insects’ seasonal behavior is also affected by climate. The birds have to move their egg-laying dates to adapt. Egg collections are such a fascinating tool for us to learn about bird ecology over time. I love the fact that this paper combines these older and modern datasets to look at these trends over about 120 years and help answer really critical questions about how climate change is affecting birds.”

Bates advises, “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.”