Spatial Vision in Birds: Anatomical investigation of spatial resolving power
Avian eyes are big both in relative and absolute terms, thus the importance of vision to birds is obvious. Even though the general eye plan is rather conservative throughout the group, there is a great variation in visual capabilities. In this thesis I present four studies on different aspects of sp...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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Department of Biology, Lund University
2015
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| Online Access: | https://lup.lub.lu.se/record/7865188 https://portal.research.lu.se/files/5742181/7865272.pdf |
| Summary: | Avian eyes are big both in relative and absolute terms, thus the importance of vision to birds is obvious. Even though the general eye plan is rather conservative throughout the group, there is a great variation in visual capabilities. In this thesis I present four studies on different aspects of spatial vision in parrots, procellariiform seabirds and birds of prey. In Paper I we studied retinal ganglion cell topography and anatomical spatial resolution in two Australian parrots, budgerigar and Bourke’s parrot, inhabiting open terrain. Differently than expected, we did not find a horizontal visual streak, an elongated area of increased ganglion cell density, which would be predicted by the “terrain theory”. In addition, we found that anatomical spatial resolution based on ganglion cell density is lower than behaviourally determined visual acuity. In Paper II, we compared spatial resolution and optical sensitivity in two procellariiform seabirds with contrasting nesting and foraging strategies. As predicted, the Leach’s storm-petrel had lower visual acuity than the Northern fulmar, however similar optical sensitivity at the level of single rod photoreceptor. Additionally, both species had a well-pronounced horizontal visual streak that supports the “terrain theory”. In Paper III, we studied the development of the visual and olfactory system in the Leach’s storm-petrel juveniles. Our results indicated, that fine-tuning of retinal ganglion cell topography does not happen early in development, and that the ganglion cell layer continues to mature throughout the nest period. In addition, we found that two-weeks old juveniles lack basic phototactic and optokinetic reflexes. In Paper IV we used transmission electron microscopy and immunohistochemistry to investigate the presence of double cones in the foveae of the red kite, common buzzard, Eurasian sparrowhawk and peregrine falcon. The double cone-free zones in the central fovea differed in size between species. We also found double cone-free zone in the temporal fovea ... |
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