|
Lorenz's Water Shrews - from "King Solomon's Ring" (1952)
In a territory unknown to it, the water-shrew will never run fast except under pressure of extreme fear, and then it will run blindly along bumping into objects and usually getting caught in a blind alley. But unless the little animal is severely frightened, it moves, in strange surroundings, only step by step, whiskering right and left all the time and following a path that is anything but straight. Its course is determined by a hundred fortuitous factors when it walks that way for the first time. But after a few repetitions, it is evident that the shrew recognises the locality in which it finds itself and that it repeats, with the utmost exactitude, the movements which it performed the previous time. At the same time it was noticeable that the animal moves along much faster whenever it is repeating what it has already learned. When placed on a path which it has already traversed a few times, the shrew starts on its way slowly, carefully whiskering. Suddenly it finds known bearings, and now rushes forward a short distance, repeating exactly every step and turn which it executed on the last occasion. Then, when it comes to a spot where it ceases to know the way by heart, it is reduced to whiskering again and to feeling its way step by step. Soon another burst of speed follows and the same thing is repeated, bursts of speed alternating with slow progress. .... Once the shrew is well settled in its path-habits it is as strictly bound to them as a railway engine to its tracks and is unable to deviate from them by even a few centimetres. If it diverges from its path by so much as an inch, it is forced to stop abruptly, and laboriously regain its bearings. The same behaviour can be caused experimentally by changing some small detail in the customary path of the animal. ... [The shrews] were accustomed to jump on and off the stones which lay in their path. If I moved the stones out of the runway, placing both together in the middle of the table, the shrews would jump right up into the air in the place the stone should have been; they came down with a jarring bump, were obviously disconcerted and started whiskering cautiously right and left, just as they behaved in an unknown environment. And then they did a most interesting thing: they went back the way they had come, carefully feeling their way until they had again got their bearings. Then, facing round again, they tried again with a rush and a jump and crashed down exactly as they had done a few seconds before. Only then did they seem to realise that the first fall had not been its own fault but was due to a change in the wonted pathway and now they proceeded to explore the alteration, cautiously sniffing and bewhiskering the place where the stone to have been. This method of going back to the start and trying again always reminded me of a small boy who, in reciting a poem, gets stuck and begins again at an earlier verse. [Lorenz 1952 p127]. |