In the column “Since You Asked” in every issue of BirdWatching, Contributing Editor Julie Craves answers readers’ questions about birds and bird behavior. Here is a question from our April 2016 issue:
A robin built a nest near my window, laid an egg, and then left. Will she come back? — Jamie Young, Springfield, Pennsylvania
Yes! The robin will lay one egg each morning until her clutch is complete — usually four eggs. After the last egg is laid, she will incubate for 12 to 14 days. By not sitting on her eggs until all are laid, she ensures that each will hatch around the same time and that none of the chicks will have a size advantage over nestmates.
Most songbirds utilize this strategy, although some sit on eggs for varying lengths of time prior to completing the clutch, often not really warming the eggs enough for them to begin development.
Some species, including many raptors, start incubating as soon as the first egg is laid, resulting in chicks of different sizes. If food is limited during the nestling period, only the older, stronger chicks will survive.
About Julie Craves
Julie is supervisor of avian research at the Rouge River Bird Observatory at the University of Michigan Dearborn and a research associate at the university’s Environmental Interpretive Center. She writes about her research on the blog Net Results, and she maintains the website Coffee & Conservation, a thorough resource on where coffee comes from and its impact on wild birds.
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