Adaptive significance of avian beak morphology for ectoparasite control

2005/04/22 by Dale H. Clayton, Dale H Clayton, Brett R Moyer +9 · 183 citations
Environmental Science · Immunology and Microbiology · #Amphibian and Reptile Biology #Anatomy #Beak #Biology #Bird parasitology and diseases #Feather #Vector-borne infectious diseases #Zoology

paper · open access · doi:10.1098/rspb.2004.3036

published in Proceedings of the Royal Society B Biological Sciences 272(1565), 811-817 (Royal Society)

openalex publication_date 2005/04/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

The beaks of Darwin's finches and other birds are among the best known examples of adaptive evolution. Beak morphology is usually interpreted in relation to its critical role in feeding. However, the beak also plays an important role in preening, which is the first line of defence against harmful ectoparasites such as feather lice, fleas, bugs, flies, ticks and feather mites. Here, we show a feature of the beak specifically adapted for ectoparasite control. Experimental trimming of the tiny (1-2 mm) maxillary overhang of rock pigeons (Columba livia) had no effect on feeding efficiency, yet triggered a dramatic increase in feather lice and the feather damage they cause. The overhang functions by generating a shearing force against the tip of the lower mandible, which moves forward remarkably quickly during preening, at up to 31 timesper second. This force damages parasite exoskeletons, significantly enhancing the efficiency of preening for parasite control. Overhangs longer than the natural mean of 1.6mm break significantly more often than short overhangs. Hence, stabilizing selection will favour overhangs of intermediate length. The adaptive radiation of beak morphology should be re-assessed with both feeding and preening in mind.

Citations

• Ectoparasite virulence is linked to mode of transmission
• Experimental demonstration of the energetic cost of parasitism in free-ranging hosts

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