Prevalence of eye colobomas in wild birds: insights from a large-scale citizen science study

Colobomas are inherited defects affecting the membranes of the eye, leading to irregularities in the shape of the iris and pupil. While the causes and occurrence of colobomas have been studied extensively in humans and captive or domesticated animals, their prevalence in wild birds (which may represent interesting model organisms) remains largely unexplored. In this study, we developed a citizen science project which conducted fieldwork to assess the presence of eye colobomas in relation to species and sex, examining 58,651 individuals from 179 wild bird species across Europe. We identified 17 cases of colobomas in nine bird species during the screening. Although the overall prevalence was low (2.90 cases per 10,000 individuals), a notably higher prevalence was observed in several owl species (Strigidae), with rates exceeding 100 cases per 10,000 individuals. Among six sexed Eurasian scops owls Otus scops with colobomas, all were females, while in little owls Athene noctua, both positive cases were males. Our findings suggest that certain wild bird species could serve as valuable subjects for studying colobomas, though further research involving more extensive sampling and visual inspection, along with cytological and genetic analyses, is necessary to estimate coloboma prevalence across birds accurately.