Camouflage by edge enhancement in animal coloration patterns and its implications for visual mechanisms

Animal camouflage patterns may exploit, and thus give an insight into, visual processing mechanisms. In one common type of camouflage the borders of the coloured patterns are enhanced by high contrast lines. This type of camouflage is seen on m any frogs and we use it as the basis for speculating about vision in a small, frog-eating snake. It is argued that a simple categorization of intensity profiles, such as that invoked by a mechanism that detects phase-congruence, occurs at an early stage of snake vision. We show that edge-detectors using a phase-congruence strategy will be unable to distinguish between ‘natural’ step-edges and the enhanced border profiles commonly seen on cryptic animals, and that the camouflage will be effective over a wide range of spatial scales.

[1]  J. Behler,et al.  National Audubon Society Field Guide to North American Reptiles and Amphibians , 1979 .

[2]  John F. Canny,et al.  A Computational Approach to Edge Detection , 1986, IEEE Transactions on Pattern Analysis and Machine Intelligence.

[3]  D Marr,et al.  Theory of edge detection , 1979, Proceedings of the Royal Society of London. Series B. Biological Sciences.

[4]  M V Srinivasan,et al.  Bi-partitioning and boundary detection in natural scenes. , 1987, Spatial vision.

[5]  D. Burr,et al.  Feature detection in human vision: a phase-dependent energy model , 1988, Proceedings of the Royal Society of London. Series B. Biological Sciences.

[6]  P. Gregory.  Feeding habits and diet overlap of three species of garter snakes (Thamnophis) on Vancouver Island , 1978 .

[7]  H. Cogger.  Reptiles and Amphibians of Australia , 1975 .

[8]  C. W. Radcliffe,et al.  Effects of Chemical and Visual Stimuli Upon Chemosensory Searching by Garter Snakes and Rattlesnakes , 1981 .

[9]  Robyn A. Owens,et al.  Feature detection from local energy , 1987, Pattern Recognit. Lett..

[10]  J. Lythgoe.  The Ecology of vision , 1979 .

[11]  C. Carpenter.  Comparative Ecology of the Common Garter Snake (Thamnophis s. sirtalis), the Ribbon Snake (Thamnophis s. sauritus), and Butler's Garter Snake (Thamnophis butleri) in Mixed Populations , 1952 .

[12]  H. B. Kettlewell.  The Phenomenon of Industrial Melanism in Lepidoptera , 1961 .

[13]  H. B. Cott,et al.  Adaptive Coloration in Animals , 1940 .

[14]  Michael F. Land,et al.  Cone mosaic observed directly through natural pupil of live vertebrate , 1985, Vision Research.

[15]  R O Wong,et al.  Morphology and distribution of neurons in the retina of the american garter snake Thamnophis sirtalis , 1989, The Journal of comparative neurology.

[16]  D. Hubel,et al.  Receptive fields, binocular interaction and functional architecture in the cat's visual cortex , 1962, The Journal of physiology.