Parental Recognition of Offspring in the Cliff Swallow

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Abstract
We examined variation in the calls and facial patterns of Cliff Swallow (Hirundo pyrrhonota) chicks to test the prediction that, in species in which dependent young intermingle, coloniality necessitates parent-offspring recognition and thus favors the evolution of highly variable "signature" traits. The calls of Cliff Swallow chicks were found to be highly distinctive: interindividual variation was significantly greater than intraindividual variation for five measured parameters. Playback experiments indicated that parents could locate their chicks by these signature calls alone. We found that chick faces were individually distinctive as well. Chick faces could be readily distinguished by human observers, although we did not test whether or not Cliff Swallow parents actually use this information. Studies of several swallow species implicate coloniality as the variable in this family that separates species with distinctive chick signatures and strong parental recognition [Cliff Swallows and Bank Swallows (Riparia riparia)] from species in which these traits are weak or absent [Northern Rough-winged Swallows (Stelgidopteryx serripennis) and Barn Swallows (Hirundo rustica)].