Descriptive histological analysis of the upper, lower, and third eyelids and the conjunctiva-associated lymphoid tissue in birds of prey

Despite some common features, the upper, lower, and third eyelids of raptors from the orders Accipitriformes, Falconiformes, and Strigiformes exhibit significant morphological variation. The third eyelid and conjunctiva-associated lymphoid tissue (CALT) display the most diverse structures among the analyzed species. Owls stand out as a group of raptors with the most distinct eyelid morphologies, both compared to other raptors and within their own group. The small number of birds may lead to difficulties in distinguishing individual variation from species-specific traits, as we cannot be certain whether the observed differences result from genetic or environmental factors specific to the individual birds or if they are traits typical for the species. To address this issue, further studies involving a larger number of individuals from the same species are necessary to more accurately determine whether the morphological traits described in this study are consistent within the species or if significant variation exists among individuals.