Thursday, 5 February 2009

The affair of the sap-sucking woodpeckers.

On page 51 of Oliver Rackham’s recent book ‘Woodlands’ he writes of the sap sucking habits of the American ‘sapsucker’ bird. Then he continues to describe the antics of the great spotted woodpecker in the same context. As Dr. Rackham is the leading scholar in landscape history his comments must be taken seriously. He says ‘it is curious that such a conspicuous activity was not noticed in bird or forestry books down the centuries’. Indeed it is so, if so. Rackham states that the activity has been noticed in Central Europe since the 1930’s. He did not observe it in England before the 1970’s.
What is the activity? The bird makes a series of small holes aligned horizontally on a tree trunk. The holes are about a centimetre wide and deep. The tree is healthy and sap exudes out of the holes which the bird then laps up with its rather long tongue. The birds may make many rows of such holes in a trunk. In young trees such as chestnut or lime the bark is often somewhat smooth and the holes are then very easy to see. I have seen them in the Forest of Dean but not here in southern France. Rackham states that the holes ‘ seem ’ to be caused by the bird. That suggests a note of caution. When I first saw these rows of holes in the Dean an RSPB colleague suggested it might be the work of nuthatches. They frequently jam acorns into cracks in bark in order to eat them. Could they make holes in smooth barked trees in order to do this? But a little research convinces me that the wood-pecker is indeed the artisan.
A friend, resident in Bishop’s Stortford, who is an excellent bird-watcher drew my attention to the note in Rackham’s work, with some comment of surprise since he had not seen the phenomenon and indeed as noted - it is not mentioned in the general English works on birds. But I have found reference to it on both Swiss and Belgian web sites. Also I read in my popular French bird guides that both the great spotted and the black woodpeckers feed on sève (i.e. sap), though it is not explained how. Is this a longstanding commonplace phenomenon on the continent? Is it a trick learnt by the birds just as milk bottle top opening was a trick acquired by tits and then passed on from bird to bird?
The great spotted species [ pic épeiche ] is amongst the commonest of our woodpeckers. I illustrate an immature bird. There are two others which look very similar, the middle spotted and the lesser spotted. The latter is very tiny, about the size of a chaffinch. The larger species is more the size of blackbird.