Einstein Science Reporting for Kids
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6-Aug-2004

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Share the nest, get more food



The moss covered mud nest of a flycatcher or “Eastern Phoebe” near Ithaca, NY. You can see a single, baby Brown-headed Cowbird and several young flycatchers. The cowbird chick begs intensively by raising its head higher and more frequently than the young flycatchers. Image © Mŕrk E. Hauber.
Click here for a high resolution photograph.

Sharing the nest helps some baby birds grow faster, according to new research. A team of scientists studied the babies of "brown-headed cowbirds" -- birds that lay eggs in the nests of other kinds of birds, such as flycatchers. The researchers found that baby cowbirds grow faster when they are raised in a nest with two flycatcher parents and two flycatcher babies than when they are raised in a nest with two flycatcher parents and no other babies.

The scientists say that three begging babies in one nest (one cowbird parasite and two flycatchers) motivates the parents to bring back more food – squished flies – than the hunger cries and body language from one baby cowbird.

When sharing a nest with two flycatcher babies, a cowbird baby usually gets more than its fair share of the squished flies.

Scientist Rebecca Kilner thinks the cowbirds grab more of the food because they perk up and opened their mouths quicker once the parents return with beaks full of food.



In experiments that mimic the actions of birds in the wild, scientists placed cowbird eggs (brown speckles) in flycatcher nests. Cowbird eggs typically hatch four to five days earlier than the flycatcher eggs. One or more flycatcher (phoebe) chicks regularly survive alongside the cowbird. Despite the differences in color and size between the cowbird and flycatcher eggs, flycatcher parents do not eject cowbird eggs. Image © Mŕrk E. Hauber.
Click here for a high resolution photograph.

The scientists returned to the nests regularly to weigh the babies and measure one of their leg bones called the tibia. In their paper appearing in the 06 August 2004 issue of the journal Science, the scientists report that nest-sharing cowbird babies grew faster than cowbird babies raised without other babies in the nest.

Cowbirds are not the only birds to lay their eggs in other birds' nests. Cuckoos also force other kinds of birds to raise their babies but, unlike cowbirds, baby cuckoos kill their neighbors in the nest soon after hatching. This study shows that sharing the nest provides personal benefits to cowbird chicks -- they attract more food from adults. The research could help explain why the babies of about half of the world's "parasite birds" -- those that regularly make other birds raise their young -- share the nest with other baby birds.

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Q & A: A related Q & A with two kids and the corresponding author.

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