Meeting Abstract

P1.132  Friday, Jan. 4  Comparative morphology of owl and hawk extraocular muscles FRASER, A*; SEGEV, T; GRAW, WA; SUCHOCKI, L; HALL, MI; Midwestern University; Midwestern University; Midwestern University; Midwestern University; Midwestern University fraser62@gmail.com

Every vertebrate has six extraocular muscles that attach to the optic globe for the purposes of eye movement. Birds have two additional muscles attached to superior and inferior nictitating membranes, transparent membranes that can be drawn over the eye for protection. Owls and hawks are both relatively large-bodied, predatory groups of birds. Both groups use visual cues to hunt and as such exhibit large relative and absolute eye sizes. Hawks appear to have extraocular muscle function similar to other vertebrates in that they utilize eye movements to observe visual space. However, owls do not utilize extraocular motion and instead have evolved elaborate neck movements to observe visual space. While owls do not appear to move their eyes at all, they do retain reduced extraocular muscles in the same configuration as all other vertebrates. To date owl extraocular muscles have not been described. In this study, we describe owl extraocular muscles by comparing them to hawks. We dissected and observed extraocular muscles of eight birds of varying body size, including two barn owls (Tyto alba), two Great Horned Owls (Bubo virginians), two Red-tailed Hawks (Buteo jamaicensis), and two Harris Hawks (Parabuteo unicinctus). The extraocular muscles were removed and weighed to obtain relative sizes, and then prepared for histology and individual muscle fibers were counted. We discovered that hawks consistently have larger extraocular muscles than do owls, even when accounting for eye size and body size differences. However, the two additional muscles attached to the nictitating membranes were also reduced in the Barn Owl, but not in the Great Horned Owl.