Abstract
Beak abnormalities have been reported in a wide range of species but typically affect only a small portion (<1%) of wild bird populations. Most research has focused on the prevalence, morphology, and causes of beak deformities, resulting in relatively little information on the consequences of these deformities for individual birds. Birds with abnormal beaks likely struggle to feed themselves, a situation that can only be exacerbated during the breeding season when they must provide food for not only themselves but also their offspring. We captured a female house wren (Troglodytes aedon) with abnormal mandibles during the 2016 breeding season. The female was lighter and smaller than normal, and her clutch size smaller and incubation and nestling periods slightly longer than normal. Using video recordings at the nest, we found that early in the nestling period the female's provisioning rate was lower and her time spent brooding greater than normal, yet she succeeded in rearing a smaller-than-average brood. We conclude that the female's abnormal beak was a severe handicap negatively affecting both her condition and her provisioning ability; however, it did not preclude her from raising a brood of nestlings.