18 April 2004

(30) Learning

There are those who tell me that the feats of corvids are not that exceptional: other birds are able to do the same as these corvids. Then they come up with stories of Galapagos finches that use 'tools' (sticks to probe into wood and catch caterpillars or termites), starlings and parrots that are able to mimick many sounds (from nature, machines, humans, other beings), herons that use 'bait' to catch fish, and so on.

I already knew these stories of other bird species and many, many more. What intrigues me, is that corvids, especially crows, ravens and jays are able to perform ALL of these 'tricks'. What I and others experienced is, that they are quick in the uptake of some new 'technique' if there is a chance it will give them an advantage in getting food. They can be seen to be intent upon watching other (bird) species and learn whatever way these other creatures catch food. And immitate the tricks almost impeccably, after a few trials. Or else they discover or invent some new manoeuvre to do the same. All this in such a short time that one can almost be sure they do it with insight, thinking, and not simply with a lot of luck.

The last thing I would expect of any bird that is not water fowl, is to hunt in water. Ducks, geese, swans, boobies, cormorants,water-hens, gulls and all those birds with protective fatty layers in their body and oiled feathers are able to swim and dive without any problem. Kingfishers are able to dive in quickly and have to get out of the water as fast as possible. Eagles can snatch fish from the surface of a lake, but when they accidentally ( a heavy salmon ) land into it they haphazzardly have to peddle with their wings to the nearest shore to prevent a certain death by drowning.
Although I've never seen them do it myself, I know of at least two stories where people claim they have seen ravens or crows dive in and/or swim under water to hunt.

One story is from "A Notebook of Birds 1907-1980" (Macmillan, London 1981, pages 17 & 18). It's from John Hughes:
" In early June 1973 I witnessed a pair of Carrion Crows, Corvus Corone, plunging into the River Severn at Shrewsbury, Salop, to catch fish. One crow jumped feet first from a concrete ledge into the water and remained totally immersed for a few seconds before reappearing with a fish in its bill. The second crow received the captured fish and dashed it several times on the ledge. The dead fish was then taken to some young crows perched on the roof of a nearby building. The whole operation lasted about 20 minutes and was repeated several times, each time successfully. The crows took turns in the fishing and killing operations."
Then the commentary of the editors:
" There are many instances of Carrion Crows taking fish and other food from water (...) but this observation is exceptional. The success rate was high even for terns Sterna or kingfishers (Alcedinidae) while the fact that two crows should have learned to plunge right under water is very remarkable."

The other story I took from "Life Histories of North American Jays, Crows and Titmice" by Arthur Cleveland Bent (the Dover Publications edition, New York 1988, two volumes bound as one, page 194). I must admit I have my doubts about this story, but perhaps I simply misunderstood it. Here it is ( by Kumlien,1879):

" I have, on different occasions, witnessed them [-northern ravens-] capture a young seal that lay basking in the sun near its hole. The first manoeuvre of the ravens was to sail leisurely over the seal, gradually lowering with each circle, till at last one of them dropped directly into the seal's hole [-into freezing cold water, as I understand it! A.-], thus cutting off its retreat from the water. Its mate would then attack the seal, and endeavor to drag and drive it as far away from the hole as possible. The attacking raven seemed to strike the seal on the top of the head with its powerful bill, and thus break the tender skull."