Western Kingbird (Tyrannus verticalis) with bill deformity in Memphis, Tennessee, USA

Bill deformities have been documented in many avian species across the globe and can be caused by environmental or genetic conditions that may also reflect ecosystem health. We describe the first case of bill deformity in the genus Tyrannus, in a young male Western Kingbird (Tyrannus verticalis) that fledged from a nest in an industrial park in Memphis, Tennessee, USA. The upper mandible of the bill was curved to the left and below the plane of the normal lower mandible making it unlikely that the individual would be able to forage normally and survive to adulthood. Genetic testing for evidence of hybridization with Scissor-tailed Flycatchers (T. forficatus) showed no sign of introgression, and it is unclear what caused the deformity.