The keratin layer of the beak becomes overgrown, resulting in elongated and often crossed beaks. The deformity showed up in adults birds, most often in the upper beak but sometimes in the lower beak or both. The abnormality — sometimes accompanied by elongated claws, abnormal skin or variations in feather color — impacts a bird’s ability to feed and clean itself.
Many of the birds with the deformities are eating at human-provided feeders, thankfully. Scientists are searching for the cause of such a large prevalence of cases. Environmental pollution is a likely candidate.