Morphological Study of the Iris Musculature in Diurnal and Nocturnal Raptors Estudio Morfológico de la Musculatura del Diafragma en Aves Rapaces Diurnas y Nocturnas

& Elisabetta GiannessiCOLI, A.; STORNELLI, M. R.; BARSOTTI, G.; CECCHERELLI, R.; GIANI, E.; LENZI, C. & GIANNESSI, E. Morphologicalstudy of the iris musculature in diurnal and nocturnal raptors. Int. J. Morphol., 34(2):503-509, 2016.SUMMARY: In literature it is established that the iris musculature consists of striate muscle fibers in birds while in mammals itconsists of smooth muscles. Some authors report the presence of smooth muscle tissue also in the iris of some species of birds. In thepresent study we report on the iris muscle tissues (type of tissue, direction and mean diameter of muscle fibers or cells) in f ive species ofAccipitriformes (diurnal raptors) and four species of Strigiformes (nocturnal raptors) because they show different way of life dependingof their predatory behavior. This morphological study was carried out from raptors died or euthanized at the Wild Life Rescue C entre ofSea and Water birds in Livorno (Italy). From histological examination of iris serial radial sections we find both striated and smoothmusculature even if with marked differences among analyzed species, not directly correlated with diurnal or nocturnal lifestyle . Striatedfibers are always present, mainly with cross direction, throughout the iris stroma, while the histological differences concern the smoothcells. Indeed, harrier and sparrow hawk (Accipitriformes) and great horned owl and little owl (Strigiformes) show a compact layer ofcross smooth muscle cells throughout the iris stroma. In the other species analyzed smooth muscle cells are slightly detectable asscattered or not detectable. Since the cross smooth muscle tissue allows to maintain a myotic state for extended periods of time, ourresults might be correlated more to the predatory behavior than the taxonomic order.KEY WORDS: Iris; Striated musculature; Smooth musculature; Morphology; Raptors.