Animal Dummies and Models – how could ethologists live without them
Dummies and models of animals can be very useful especially in studies that focus on big animals and those that move around much. One such use of models involved those of cows; cows with a pure white and a pure brown coat and models of white cows with 8, 16, and randomly distributed 64 brown patches on the white background fur.
These dummy cows were then painted with a sticky glue and placed out in the open on a paddock that was used by real cows for grazing. Why this elaborate set-up by my friend Prof. Gabor Horvath and co-workers? Because Horvath and colleagues had earlier shown that many insect species exhibit polarotactic visual behaviour and can distinguish linearly polarized from unpolarized lights. In particular polarizing water surfaces, but also asphalt roads, black plastic sheets, marble grave stones and black limousines were attractive to them. So what about black/white spotted cows?
Prof. Horvath hit upon the idea to test the attractiveness of cows with differently polarizing coat patterns to tabanid flies (also known as gadflies), because the latter are considered a nuisance in animal husbandry as they annoy cattle and other grazers and prevent them from feeding peacefully. The results were unequivocal: the fully brown cow dummies had the largest number of tabanid flies stuck on them while the spottiest dummies had attracted the least number of flies. The researchers followed up their results with measurements from real cows to confirm if it was the degree of polarized light reflected from a cow’s coat that was involved. And lo and behold, dark brown cows reflected the highest amount of polarized light, but cows with bright and dark patches reflected light with different degrees of polarization and angles that interfered with the tabanids’ (= gadflies’) recognition of their target animal.
Horvath and colleagues then turned their attention to the question why zebras were striped. Could it be that the stripes were an adaptation to disrupt the polarization pattern and thus reduce the animal’s attractiveness to the biting flies? Once again they used near life-sized dummies, but this time of black, brown, white and zebra-striped horses. With the cattle results already in, it was perhaps not exactly surprising to find that the striped model was least attacked by the tabanids and that zebras could have evolved to have the characteristic white stripes on a black coat as an adaptive response to tabanid and other fly attacks.
Another kind of dummy, this time with a human inside, was used by Eigil Reimers and Sindre Eftestøl in order to find out at what distance reindeer on the Svalbard Archipelago would take flight when approached by a hiker or a polar bear. The dummy polar bear consisted of a human, totally wrapped in white cloth with three black spots painted on it on the head to indicate the bear’s black nose and its eyes. The hiker wore the normal outfit of a hiker. The observations were carried out during the day and there were, of course, the problems of size and contrast between dummy and real bear and dummy and hiker. However, reindeer were found to flee at significantly greater distances from the dummy bear than from the hiker, suggesting that the reindeer responses indicated a predator prey relationship that had not yet developed to the same extent between humans and reindeer on the Svalbard.
I couldn’t help thinking of these dummy experiments driving along country roads in Japan and seeing in the distance the cut-out and painted shapes of policemen or traffic wardens. If those dummies were thinking anything at all, they must have wondered if I’m dumb enough to fall for their ploy!
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2019.
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