Beak abnormality hinders provisioning ability and reduces body condition of a female House Wren (Troglodytes aedon)

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.

Functional traits and foraging behaviour: Avian vampire fly larvae change the beak and fitness of their Darwin's finch hosts

“…In this study: (1) We predict that Darwin's finch beaks with enlarged nares will be used more often to glean and pick prey exposed on the surface, and less often for techniques that require high pressure on the beak, such as chipping, prying and probing for prey hidden beneath bark; (2) If birds with malformed beaks have convergent foraging behaviour, there may be shifts in foraging overlap between previously diverged species. We predict greater interspecific foraging niche overlap in birds across species with extreme naris size enlargement; (3) We expect to find a smaller coefficient of variation in naris size in beaks used for subsurface prey extraction than surface prey removal; and (4) Although we do not measure prey size or items consumed, we predict that birds with malformed beaks will have lower body condition, not least because of known associations between foraging efficiency and beak size and shape in Darwin's finches (Grant & Grant, 2014a), as well as lower body condition in other avian species with malformed beaks (Hodges et al, 2019).…”