Case study: Beak deformity of a Monticola solitarius individual in Gavdos, Crete

Abstract

Beak deformities in the wild are a rare sight as the deformity reduces the individual’s ability to feed, maintain the plumage and attract mates while increasing the susceptibility to infections, thus significantly impacting the individual’s fitness. The etiology of a beak abnormality can be caused by anatomical maldevelopment, and/or a keratin disorder caused by nutritional deficiencies, infections (bacterial, viral, fungal, or parasitic) or exposure to environmental toxins, primarily agrochemicals. We report here the case of an extreme, debilitating crossbill deformity of a male blue rock thrush trapped on the island of Gavdos during a bird ringing survey in May 2022. The individual was estimated as being at least one year old based on its plumage and in a good body condition, with normally developed and maintained feathers. The survival of this individual, seemingly incapable of using its beak to manipulate food items is difficult to explain, especially since Gavdos does not provide soft easily manipulated food apart from olives and some berries and figs. The only other food that could provide sustenance on Gavdos are snails and possibly, bees and other insects. However, the extent of the deformity would severely impede preying on a hard-bodied prey such as snails or beetles, with preying on moving venomous prey that needs to be first stunned such as bees even less likely. The survival of this individual demonstrates a fascinating adaptive response to environmental conditions through problem solving, as well as the plasticity of the dietary niche capable of sustaining an individual.