Crocodile Birds
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[edit] Definition
[edit] The crocodile bird in Classical texts
The first description of such behavior appears in Herodotus (5th century BC):
- The following are the peculiarities of the crocodile ... as it lives chiefly in the river, it has the inside of its mouth constantly covered with leeches; hence it happens that, while all the other birds and beasts avoid it, with the trochilus it lives at peace, since it owes much to that bird: for the crocodile, when he leaves the water and comes out upon the land, is in the habit of lying with his mouth wide open, facing the western breeze: at such times the trochilus goes into his mouth and devours the leeches. This benefits the crocodile, who is pleased, and takes care not to hurt the trochilus. (Herodotus, Histories, 2:68[1])
There are various points to note here. In the original claim, the bird is removing parasites from the mouth, rather than caring for the dental hygiene of the crocodile. Herodotus does not describe the bird which he calls the "trochilus" in any detail, so there is no reason to identify it as the Egyptian plover. Finally, note that Herodotus, who has been criticized by later historians for his gullibility, does not claim to have seen this himself.
The teeth-cleaning version of the story crops up in Aristotle in the 4th century BC:
- When the crocodile yawns, the trochilus flies into his mouth and cleans his teeth. The trochilus gets his food thereby, and the crocodile gets ease and comfort; it makes no attempt to injure its little friend, but, when it wants it to go, it shakes its neck in warning, lest it should accidentally bite the bird. (Aristotle, History of Animals, Book 9 ch. 6 [2])
In Pliny the Elder's Natural History (1st century AD), more details, even less credible, are given:
- When [the crocodile] has glutted itself with fish, it goes to sleep on the banks of the river, a portion of the food always remaining in its mouth; upon which, a little bird, which in Egypt is known as the trochilus, and, in Italy, as the king of the birds, for the purpose of obtaining food, invites the crocodile to open its jaws; then, hopping to and fro, it first cleans the outside of its mouth, next the teeth, and then the inside, while the animal opens its jaws as wide as possible, in consequence of the pleasure which it experiences from the titillation. It is at these moments that the ichneumon, seeing it fast asleep in consequence of the agreeable sensation thus produced, darts down its throat like an arrow, and eats away its intestines. (Pliny, Natural History Book 8 ch. 37 [3])
In the next chapter he describes how dolphins with sharp fins gut crocodiles by swimming underneath them.
We have not been able to find out at what point the trochilus was identified with the Egyptian plover; it is brightly-colored, conspicuous, and common on the banks of the Nile, and this may have stimulated the identification.
[edit] Discussion
There seems to be no evidence for the existence of the crocodile bird besides the tales of these classical authors. As their works are demonstably full of wild erroneous tales, none of them claims to have seen the trochilus, and few of them had visited Egypt, we need not give much weight to their accounts.
In the modern scientific literature on natural history, there are no accounts of this behavior[4]. Moreover, there appear to be no films or photographs of any bird grooming a crocodile's mouth. This would be surprising if this symbiotic relationship existed, given the eagerness of documentary film-makers and photographers to show us interesting facets of animal behavior; and more surprising when one reflects on how many camera-wielding tourists travel along the Nile each year. For a charming digital fake of an Egyptian plover in a crocodile's mouth, see here.
It is also hard to see how such a symbiotic relationship could have evolved, since it would seem that the first bird to hop into a crocodile's mouth would be eaten. Indeed, the supposed existence of the crocodile bird has been used as the basis of a creationist argument for this very reason (see the section on creationists and crocodile birds, below).
Despite the apparent non-existence of any such bird, the myth of the crocodile bird has proven very pervasive, possibly because of its intrinsic charm, and has even found its way into textbooks as an example of symbiosis.
[edit] Creationists and crocodile birds
Creationists often cite the crocodile bird amongst their little list of things which they think couldn't have evolved. In the case of the crocodile bird, they may for once be right; but biologists do not have to account for the evolution of nonexistent mythical creatures. Here is a sample creationist argument:
- Consider the crocodile bird. The crocodile holds its mouth wide open and the bird walks in and cleans the teeth and gums, removing ticks and other parasites. The arrangement is advantageous to both, but how did it get started? The instinct to walk into the open mouth of a crocodile will not be developed by Natural Selection unless the birds that do it are likelier to survive than the ones that don't, and this will not be the case until considerably more than 99.999% of all crocodiles had a built-in instinct to refrain from eating them, and the crocodiles would have had no reason to develop such an instinct until the birds had an instinct to groom them. [5]
In fairness to creationists, we should point out that for once they are not solely responsible for the propagation of the myth, and that the legend of the crocodile bird has found its way not only into creationist literature, but also into books intended to have a genuine educational purpose.
