Eating Habits of Reptiles (Last Part)

The idea of a poisonous animal evolving a warning device that will work only if a potential enemy also evolves the sense to react to the warning is hard for some people to accept. I do not know why this should be so. Besides logic, a great store of anecdotal evidence supports its reality. Nearly any mature retriever dog, for instance, reacts instantly to the sound of a rattlesnake. While it is hard to be sure what a dog has learned from previous experience or from other dogs, it can, in most of the cases, be certain the learning process did not involve being bitten by a rattlesnake. If you saw your dog suddenly jump into the air and you went to the spot to see what had scared it, one of two things was most often there—a coiled diamondback, or a bush of a certain species of Crotalaria, the dry pods of which rattle when disturbed, almost like a rattler’s alarm. Only one of the several species of Crotalaria sounds authentically like a snake, and only that species used to make the dog jump. But the effect of a collision with that was electric, and for all the years of its life the dog rose like a bird when it stirred the fearful noise from a diamond back or from the bush that I think sounded the same to the dog.

That is of course not a scientific observation. And in any case it leaves unanswered the question of whether the reaction is innate in canines or is learned by associating the sound of the rattle with the bites or aggressive behaviour of snakes in general—or is learned from other dogs. That dogs are of Old World, and rattlesnakes of American origin, makes it seem unlikely that the pointer was born genetically able to associate the sound with the snake. On the other hand, the buzzing of rattlesnakes is really just an elaboration of a tendency of many kinds of snakes to vibrate the tail when approached by a potential enemy. The vibration is often soundless, but in dry leaves it makes a little rattling or humming noise. Possibly dog ancestors evolved the capacity to associate such a sound with ill-tempered or dangerous snakes. But the important point is that the rattle of the rattlesnakes makes little sense unless it can be thought of as an agent of advantage to the bearer. And the advantage in not being stepped on by a bison or chopped up by the teeth of a wolf seems pretty clear. That the bison and wolf might go away poisoned and die would be little comfort to the snake. Its profit would come from preventing the encounter from happening.

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