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How an uninvited bird guest fools its hosts

Click here for a high resolution photograph.

When a female Horsfield's hawk-cuckoo lays an egg, she leaves it in the nest of other birds, where the chick will be raised by foster parents. Animals have many different strategies for survival, and the hawk-cuckoo chick's isn't particularly kind. It pushes the other baby birds out of the nest, so that it can receive all the attention from its foster parents.

Researchers have now discovered a way that this bird tricks its foster parents so they don't notice that the other babies are missing. They report their findings in the 29 April issue of the journal Science.

Click here for a high resolution photograph.

The puzzling thing about the hawk cuckoo and other "parasite" birds that evict the other babies from the nest is that bird parents usually need to see more than one open mouth in order to start feeding their young. That's why baby birds are often seen all with their beaks wide open: together, the beaks send a "feed us" signal to the parents.

But, if the hawk cuckoo is the only chick in the nest, how does it get the parents to feed it?

Keita Tanaka and Keisuke Ueda of Rikkyo University in Tokyo, Japan wondered if the answer might involve the two bright yellow patches on the Horsfield's hawk-cuckoo's wing. When the cuckoo chick makes these patches quiver, it might look to the parents like two extra open mouths.

The researchers tested their idea by hiding the chicks' wing patches with black paint. They found that the chicks received less food from the parents. A logical explanation is that the quivering yellow wing patches were indeed tricking the parents into feeding the chick more food.

Even though the wing patches aren't really shaped like open beaks, they are somewhat close in color. The authors propose that in the dark nest, the parents can't tell the difference.