Chronic. The capacity for social learning is a skill that anthropologists bestow on the human species but which they believed, until recently, to have few prototypes in other species. More and more examples are listed – mainly in monkeys or in certain birds – where individuals copy the behavior of their elders or their peers.
A new species is now proposed as a model of competence, and more particularly in the field of protective behavior against human predations. It’s about sperm whales, the subject of a fascinating article that appeared this month in a biology journal (“Adaptation of sperm whales to open-boat whalers: rapid social learning on a large scale? “, Hal Whitehead, Tim D. Smith and Luke Rendell, Biology Letters, March 2021).
The authors rely on the archives of American whalers in the North Pacific Ocean during the XIXe century. They extracted a sample of 77,749 travel days, of which about 3% resulted in sperm whale spotting. By observing for each sighting whether the whaler succeeded in capturing the animal, the authors find a rapid drop in the success rate during the five to ten years after the first exploitation of each region of the ocean.
They could spread their distress to others
It seems that the whalers have become less efficient at hunting, or the sperm whales more efficient at escaping. But why, and how? The authors establish four alternative hypotheses. The first: less efficient whalers who exploited each region lagging behind the first, more enterprising. But looking at the success rate of these two groups of whalers in other parts of the Pacific, the authors do not find a systematic difference.
Second hypothesis: it would be the weaker sperm whales that succumb to the hunt first, leaving the more agile and clever to face the hunters on subsequent expeditions. This hypothesis does not seem capable of explaining such a sudden drop in the success rate, given the typical proportion of immature or old sperm whales in the population.
Third hypothesis: sperm whales learn from a first encounter with whalers how to better escape them during future encounters. This seems unlikely to explain the drop in the success rate given the low proportion of the total sperm whale population spotted each year.
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