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 June 2017 issue.
Why don’t birds build better nests? It seems like some always fall out of trees in storms, and it is not unusual for me to see baby birds that must have fallen out of nests. — Adam Cox, Harrisburg, Pennsylvania
First, the baby birds you are seeing likely aren’t accidentally falling out of nests. It is perfectly normal for most songbirds to be unable to fly when they leave the nest. A nest full of young birds being visited continually by parents filling hungry mouths is at high risk of being found by predators. It is much safer for birds to leave the nest as soon as they are feathered and able to cling to branches and move around. Parents will move them to different locations, giving each a better chance to survive.
That being said, many nests are clearly not fortresses, offering only minimal support and protection for eggs, young, and parents. This is thought to be due to a number of factors, often related to time constraints. Migratory birds in particular have a limited period during the breeding season to find and secure a territory and to mate and raise their young. Most long-distance migrants have only enough time to raise a single brood. If too many hours are spent nest-building and the nest fails, the birds won’t have enough time to attempt a second nest, and the breeding season will be lost.
Nest-building activities can attract predators or brood parasites such as cowbirds to the nest site, so spending less time on construction may minimize that risk. Too much time and energy invested in collecting nest materials and constructing a nest may leave adults less fit and able to properly care for young. Under some circumstances, more substantial nests may also be more visible to predators. Thus, there is a trade-off between the costs and benefits of having a more secure, bigger, or “better” nest.
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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