Warbler Bird Species Recognize Imposter Eggs of Cuckoos

Warblers Ward off Imposters

April 19, 2011 by  
Filed under Features

Cuckoos have never been very popular amongst other birds species. They are known to be lazy parents and have become sophisticated in their methods of camouflaging their own eggs to look like those of other species, so that they are able to introduce their own eggs into the nest and have the other birds raise their chicks. But host birds are beginning to wise up to the counterfeit eggs being laid in their nests and have developed their own skills to fight off imposter eggs.

Studies conducted at the University of Cambridge, led by Claire Spottiswoode, revealed that host birds, especially warblers, have become more vigilant in regard to recognizing imposter eggs. Most birds use one of two methods. They either teach themselves to be able to recognize the imposter eggs purely by sight, or they have taught themselves to change the coloring of their own eggs, making it more difficult for the cuckoo to copy. During the research studies, scientists placed the eggs in the nests of bird species that were closely related to warblers. It seemed to show that the red-faced cisticola was quite apt in noticing an imposter egg purely by sight, while the tawny-flanked prinia was not very confident in noticing a difference. In its defense, the prinia is able to lay a rainbow color of eggs, complete with variable patterns, which deter cuckoos from the challenge of laying eggs in their nests. In addition they are able to recognize the imposter egg due to their defenses and eject the eggs immediately. The rattling cisticola is no longer the target of the cuckoo, as it has been able to use both defenses, that of recognition and color changing of eggs, to establish which of the eggs are imposters.

Researcher Dr. Martin Stevens expressed his findings of the outcome of the studies, saying: “Our experiments have shown that these different strategies are equally successful as defenses against the cuckoo finch. Moreover, one species that has done a bit of both – the rattling cisticola – appears to have beaten the cuckoo finch with this dual strategy, since it is no longer parasitized. The arms race between the cuckoo finch and its host emphasizes how interactions between species can be remarkably sophisticated especially in tropical regions such as Africa, giving us beautiful examples of evolution and adaptation.”

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