The cuckoo is a nasty bird, but you have to give it credit for cleverness. The cuckoo mother lays her egg in the nests of other bird species, and when it hatches, the baby cuckoo immediately pushes the other eggs out. From then on, the foreign newborn enjoys full-time feeding from its host parents--who are usually half its size. The European cuckoo makes begging noises many times louder than the parents' normal chicks, fooling mom and pop into thinking they've got a desperately hungry nest. And that's not the only trick.
Now, two behavioral biologists at Rikkyo University in Tokyo, Japan, have found another diabolical cuckoo ploy. An Asian species, called the Horsfield's hawk-cuckoo, has bright orange patches on its wings. When the host parents arrive at the nest, the cuckoo chick opens its wings and wiggles these patches. Because the patches look like the gaping mouths of chicks, Keita Tanaka and Keisuke Ueda wondered if the parents might be fooled into thinking there are more mouths to feed. To test the idea, they kept track of how often cuckoos were fed in 24 nests, but they painted the wing patches of some of the chicks black.
Having the orange patches indeed made a difference. Parents fed cuckoo chicks with black patches about 15% less often than they fed those with orange patches, the team reports 29 April in Science. The parents sometimes even tried to stuff food into the faux mouths.
Tanaka and Ueda believe the ploy may be especially valuable to hawk-cuckoos because they parasitize nests that tend to be close to the ground. Here, a visual cue would allow the cuckoos to fool the parents without loud noises that might attract predators.
The study uncovers "a wonderful bit of natural history," says Rebecca Kilner, a behavioral biologist at the University of Cambridge, U.K. She points out that rather than keeping quiet to avoid attracting predators, the hawk-cuckoo may have chosen a host that is less responsive to louder begging and may only be fooled by visual cues.
Related sites
A video of the hawk-cuckoo chick in action
Tanaka's hawk-cuckoo page
Kilner's
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