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1.
Anat Rec (Hoboken) ; 296(12): 1954-70, 2013 Dec.
Article in English | MEDLINE | ID: mdl-24249399

ABSTRACT

Vultures are highly reliant on their sensory systems for the rapid detection and localization of carrion before other scavengers can exploit the resource. In this study, we compared eye morphology and retinal topography in two species of New World vultures (Cathartidae), turkey vultures (Cathartes aura), with a highly developed olfactory sense, and black vultures (Coragyps atratus), with a less developed sense of olfaction. We found that eye size relative to body mass was the same in both species, but that black vultures have larger corneas relative to eye size than turkey vultures. However, the overall retinal topography, the total number of cells in the retinal ganglion cell layer, peak and average cell densities, cell soma area frequency distributions, and the theoretical peak anatomical spatial resolving power were the same in both species. This suggests that the visual systems of these two species are similar and that vision plays an equally important role in the biology of both species, despite the apparently greater reliance on olfaction for finding carrion in turkey vultures.


Subject(s)
Birds/anatomy & histology , Eye/anatomy & histology , Retina/anatomy & histology , Animals , Birds/classification , Retinal Ganglion Cells/cytology , Species Specificity
2.
Article in English | MEDLINE | ID: mdl-23475299

ABSTRACT

Despite the large body of literature on ecomorphological adaptations to foraging in waterfowl, little attention has been paid to their sensory systems, especially vision. Here, we compare eye shape and retinal topography across 12 species representing 4 different foraging modes. Eye shape was significantly different among foraging modes, with diving and pursuit-diving species having relatively smaller corneal diameters compared to non-diving species. This may be associated with differences in ambient light intensity while foraging or an ability to tightly constrict the pupil in divers in order to facilitate underwater vision. Retinal topography was similar across all species, consisting of an oblique visual streak, a central area of peak cell density, and no discernible fovea. Because the bill faces downwards when the head is held in the normal posture in waterfowl, the visual streak will be held horizontally, allowing the horizon to be sampled with higher visual acuity. Estimates of spatial resolving power were similar among species with only the Canada goose having a higher spatial resolution. Overall, we found no evidence of ecomorphological adaptations to different foraging modes in the retinal ganglion cell layer in waterfowl. Rather, retinal topography in these birds seems to reflect the 'openness' of their habitats.


Subject(s)
Anseriformes/physiology , Ecosystem , Eye , Feeding Behavior , Retina/physiology , Vision, Ocular , Adaptation, Physiological , Animals , Anseriformes/anatomy & histology , Diet , Diving , Eye/anatomy & histology , Retina/cytology , Retinal Ganglion Cells/physiology , Species Specificity , Swimming , Visual Acuity
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