Bill deformity in a Pearly-eyed Thrasher from Montserrat, West Indies

Abstract

The causes of bill deformities in birds have been summarized in an excellent review by Pomeroy (Brit. Birds 55:49-72, 1962). Causes include genetic mutations, disease, accident, poor nutrition, and, in caged birds, an absence of bill-filing substrates (e.g., stones, coarse bark). In wild birds, however, bill deformities are most often associated with injury to the bill. Easterla and Todd (Auk 88: 677•678, 1971) reported such an apparent injury in a free-living Yellow-headed Blackbird {Xanthocephalus xanthocephalus} from Clay County, Missouri. The blackbird apparently had suffered a fractured mandible (dentary), resulting in a longitudinal fissure and jagged broken edge. The injury allowed unchecked growth and abnormal development of the rhamphotheca (horny sheath covering the bony mandibles).

Citation

Arendt, Wayne J.; Arendt, Angela I. 1986. Bill deformity in a Pearly-eyed Thrasher from Montserrat, West Indies. North American Bird Bander 11:51–52.