The cormorants have chosen this lake, the biggest gravel pit in the Colne Valley, for their roosting place. There is a group of islands in the southern end which they have made their own. The birch trees there are sickly and dying, frosted with droppings. On these short winter afternoons, upwards of a hundred and twenty birds may be seen perching there, high and low, clustered in the trees like so many huge black fruits.
Today, for the first time all week, the sky is blue. Far off to the south and east, beyond Hillingdon and Ealing, the brown breath of London rises as smog; but northwards along the valley, beyond Rickmansworth and away to the west, the horizon looks comparatively clear. Here at Harefield there is as yet little of man in the atmosphere, except for the light planes constantly circling and landing at Denham aerodrome.
Since the wind comes generally from the west, the aeroplanes usually head straight across the valley and over the lake. They fly so low that you can see into the cockpits. Once over the main road, wings wavering somewhat if the pilot is a pupil, and with the undercarriage barely seeming to clear the trees, each one then drops abruptly and vanishes behind the ridge.
When they disappear like that you are half afraid, having seen too many cheap films, that after a short delay you will hear a low-budget explosion and see a low-budget pall of smoke. But no. Disaster is always held, once more, at bay.
No mechanics service the cormorants which use the lake. Neither do the birds bother with pilots’ licences or subscriptions to the flying club. They have no need of manuals or airworthiness regulations. In flight they are perfect.
The style is basic rather than graceful, but beautiful none the less. It gets them very efficiently from one feeding area to the next, lets them escape from enemies, and allows them to perch and rest on any projection that takes their fancy.
The feet are broad and webbed; the dark skin and toes look rather clumsy wrapped round a stub of branch, but the bird appears quite comfortable and will remain there for a long time, perhaps with wings opened, slowly digesting its last gluttonous meal. The plumage is oily and dark, and the head has a peculiarly reptilian slant. It is easy to remember that the cormorant is a relatively primitive bird. Archaeopteryx might have looked out on the world through such an eye as that.
The earliest specimen of the cormorant tribe yet found in Britain turned up in Hampshire, a fossil some fifty million years old. Even at that time the technical problems of making a cormorant fly had been completely solved, the complex equations of lift, thrust, and drag neatly dealt with and given tangible form in the bird’s shape and plumage. The wingbeats that pass over the gravel works, over the pylons and the arterial road are the very same that passed over Eocene lakes and estuaries, over a Hampshire that would seem as strange to us today as the farthest comer of Brazil. In another fifty million years there will probably be similar-looking birds, perhaps even in this very spot, digesting fish and drying their wings on a planet where mankind and all its works are preserved, if at all, as fossils.
The cormorants care nothing for their illustrious ancestry. They care only about the next cropful of fish.
A bird at the end of the island planes down to the water. Swimming low, its back awash, it dives with a pouncing leap. Underwater, where we cannot see it, the most important form of locomotion is brought into play. The cormorant is said to pursue fish with the feet alone, without using the wings except occasionally as brakes. It can dive to a great depth, staying submerged for as long as seventy-one seconds, but prefers to surface to swallow its prey.
And there it is. It has come up a few yards farther out, clutching what looks like a roach. The head is tipped back; the jaws open, and down the fish goes. The neck bulges for a moment, and then, its appetite whetted, the cormorant dives for more.