Eating and Cleaning

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Science  05 Oct 2001:
Vol. 294, Issue 5540, pp. 15
DOI: 10.1126/science.294.5540.15a

Classically, the shapes and sizes of birds' bills are held to be adaptations to the type of food they eat. Clayton and Walther show that a second selective factor may be operating as well. For 52 species of Peruvian birds, they measured the abundance and diversity of ectoparasitic chewing lice that were infesting the birds' plumage. The abundance of lice was less in birds in which the upper mandible overhung the lower. An overhanging bill appears to be a more efficient tool for shearing lice by pressing them against the host's body. Thus, parasite infestation may be a selective force acting on bills, such that their morphologies might represent a compromise between the optimal shapes for feeding and for preening.—AMS

Oikos94, 455 (2001).

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