First Description of Bilateral Anophthalmia (Eyelessness) in a Western Bluebird Nestling

We report on the first documented case of bilateral anophthalmia, the congenital absence of both eyes, in a Western Bluebird (Sialia mexicana). The nestling was found in May 2022 in a nest box hung in an English walnut (Juglans regia) orchard that was part of the Putah Creek Nestbox Highway in Yolo County, California. The anophthalmic chick was part of a brood of four, of which the other three appeared normal. Anophthalmia is rarely encountered in wild birds; a literature search produced only two other records for passerines, one of bilateral anophthalmia in an American Robin and one of unilateral anophthalmia (congenital absence of one eye) in a Western Bluebird. In non-passerine birds, anophthalmia has been linked to selenium exposure and other environmental contaminants. Given the rarity of anophthalmia, documenting occurrences of birds with this and other congenital malformations may provide valuable information to clarify the costs and benefits of conserving wildlife in agricultural landscapes.