Curious Naturalists [1968] by Niko Tinbergen

Author:Niko Tinbergen [Tinbergen, Niko]
Language: eng
Format: epub
Publisher: Doubleday/American Museum of Natural History [repr]
Published: 1967-12-31T16:00:00+00:00

CHAPTER EIGHT

DEFENCE BY COLOUR

While we were busy with our studies of camouflage, we were of course, aware of the fact that many animals are not camouflaged at all, but have colour patterns that are conspicuous. A Mallard drake, a Kingfisher, and a Swallowtail Butterfly cannot be said to be camouflaged. The Peacock butterfly is beautifully cryptic (protectively concealing) when at rest, but when disturbed it either flies off, or just flaps its wings without leaving, and in both situations it is extremely conspicuous.

Of course, bright colours are not always incompatible with camouflage. A cryptic animal may be very brightly coloured, yet if its natural surroundings are equally colourful, it may be difficult to see. For instance, the bright yellow, black-banded shell of a Cepaea snail is anything but dull, yet, as the work by Cain and Sheppard has shown, it is camouflaged in certain habitats and derives considerable protection from its pattern. Even with this reservation, however, there is no doubt that many animals are the opposite of camouflaged—they are conspicuous even in their natural environment.

This was known to the old naturalists and various hypotheses have been put forward. But, as with camouflage, experimental work testing these hypotheses has not been done until quite recently, and when we started our work there was still much uncertainty. Now we know a [Page 156] good deal more. Before continuing my account of the contributions made by my co-workers, in whose studies I have taken part in one way or another, let me review the various theories that have been tested so far.

In some cases conspicuous colours have, long before Darwin, been considered to be effective in mating. Nuptial colours of many birds and other animals were considered to stimulate the females of their own kind and thus to be a means by which their co-operation in mating could be ensured. This idea has been expounded by Lorenz, who suggested that bright colours, just as sounds, postures and scents do, often function as releasers’; they serve to release appropriate responses in other animals and thus act as means of communication between individuals. Some of our own experimental work has been done with a view of testing this idea. The releaser function of a number of conspicuously coloured structures in such diverse animals as birds, reptiles, fish, crustaceans, insects and even molluscs has now been demonstrated by experiments.

Other instances of conspicuous coloration have been regarded as a means of defence against predators. These were thought to act in a variety of ways. (1) The yellow-and-black banding of wasps for instance was thought to advertise some unpleasant or repulsive quality and predatory birds were thought to learn to avoid them after a nasty experience. (2) Those in themselves harmless or perhaps palatable insects that had colour patterns similar to obnoxious ones—e.g., hover flies wearing a wasp-like pattern—were assumed to derive protection from this resemblance, the idea being that predators would, after experience with wasps, leave the hover flies alone as well. This is the hypothesis of mimicry in its strict sense.

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