A comparative study of corneal sensitivity in birds of prey

To determine and compare the corneal sensitivity in healthy wild diurnal and nocturnal birds of prey (BP) indigenous to Catalonia (Spain), and to establish if age is a determining factor in corneal sensitivity in those species.

Ophthalmic examination was performed in 105 BP. Only birds with no ocular abnormalities were included in the study (n = 81): 21 diurnal BP (Falco tinnunculus: 16 fledglings, 5 adults) and 60 nocturnal BP (20 Athene noctua [9 fledglings, 11 adults], 20 Strix aluco [15 fledglings, 5 adults], and 20 Otus scops [6 fledglings and 14 adults]). Corneal touch threshold (CTT) was determined for each eye in five different corneal regions. Five attempts to cause a blink reflex were made in each region, and when three or more reflexes were positive, the pressure was deemed the CTT. Statistical analysis was performed using a Student's t-test for independent data or an anova model. The results between species and age groups were compared using the Generalized Estimated Equations model.

There were no significant differences between any of the corneal regions (P = 0.25), or between the right (CTT = 4.9 ± 1.7 cm) and left (CTT = 4.8 ± 1.7 cm) eye in any of the species (P = 0.692). No difference was found between diurnal and nocturnal species (P = 0.913). Considering all the species, a significant difference was found between the mean CTT of fledglings (5.4 ± 1.2 cm) and adults (4.1 ± 2 cm), P < 0.001. A significant difference was found between fledglings and adults of A. noctua (P < 0.001) and S. aluco (P = 0.002).

There is no significant difference in CTT between the different corneal regions in all the species studied. Corneal sensitivity is similar between diurnal and nocturnal birds of prey. Age is a determining factor in the CTT of A. noctua and S. aluco, with fledglings having a significantly higher CTT.