woodpigeon probably represents a proportion of the total biomass approximately equal to the percentage of woodpigeons actually killed by the peregrine. The method of selection employed, if there is one, may in fact be nothing more spectacular than this: that the peregrine kills most frequently the species of bird it sees most frequently, provided it is a reasonably large and conspicuous one. The presence of abnormally large numbers of any species of bird invariably results in a higher proportion of that species being killed by the peregrine. If a dry summer enables more partridges to breed successfully, then more partridges will be taken by the peregrine during the following winter. If wigeon numbers increase when the cold weather comes, more wigeon will be killed. Predators that kill what is commonest have the best chance for survival. Those that develop a preference for one species only are more likely to go hungry and to succumb to disease.
Over the valley and the estuary, many gulls and lapwings are killed by the peregrine in October and November, chiefly from freshly ploughed land. From December to February woodpigeons are the main prey, especially in hard weather, when fewer lapwings are available. Woodpigeons are still taken in March, the killing of lapwings and gulls increases again, and more duck are killed than in any other month. Game-birds, moorhens, fieldfares, and waders, are taken occasionally throughout the winter. In rain or fog, game-birds and moorhens become the principal prey. Ducks are killed far less often than is popularly supposed. This is true of all countries, both in summer and winter; the peregrine is definitely not a ‘duck-hawk’. Domestic and feral pigeons figure highly in most lists of peregrine kills, but I have found none here. No peregrine I have seen has ever attacked them, or shown any interest in them at all.
The peregrine’s choice of prey can be affected by weather conditions. When a wet summer is followed by a wet winter, the land becomes waterlogged, ploughing is delayed, and the valley bathing-places are covered by flood-water. Peregrines then hunt over the grasslands to the south of the valley and between the two estuaries. They bathe in ditches or at the edge of flood-water. Some birds prefer to hunt over grassland, irrespective of weather conditions. These green-country peregrines arrive late in the autumn and stay till late April or early May. Possibly they come from the Lapland tundra, where the country, in summer, is like a huge emerald sponge. The wet marsh pastures, and the green fields of the heavy clay, are the colour of home to them. They range over vast distances, they fly high, they are much harder to find and follow than the comparatively sedentary peregrines of the valley. Lapwings, gulls, and fieldfares, feeding on worms in wet pastures, are their favourite prey. Clover-eating woodpigeons are taken from January to March. Nest-building rooks are often attacked.
It seems unlikely that the peregrine can have a discriminating sense of taste. If it has a preference for a certain species, it is probably because of the texture of the flesh and the amount of tender meat on the bones. Rooks, jackdaws, gulls, sawbill ducks and grebes, are all more or less distasteful to the human palate, but are eaten by the peregrine with apparent relish.
Conspicuousness of colour or pattern increases vulnerability and influences the peregrine’s choice of prey. Birds moving from place to place are always vulnerable, whether they are flying to and from their roosts along known ways, or merely passing over the territory on migration. Recent arrivals are attacked at once, before they can learn refuges. The odd are always singled out. The albinos, the sick, the deformed, the solitary, the imbecile, the senile, the very young; these are the most vulnerable.
Predators overcome their prey by the exploitation of weakness rather than by superior power. As in the following instances:
Woodpigeon
The white wing and neck feathers are visible at a great distance. White shows up against all ground-colours. The peregrine sees and reacts to white more rapidly than to any colour. Eight per cent of the birds killed in the territory were either mainly white or showed conspicuous white markings. Woodpigeons are also betrayed by the loud clatter of their wings at take-off. In spring, their display flight makes them still more obvious. Their flocks gain height too slowly, and the individual birds do not keep close enough together. They are strong in level flight; they are quick to see danger from below and to swerve suddenly aside; but when attacked from above, their reaction is less violent, they dodge with difficulty, their straight flight is slow to bend. Because they are so much shot at and disturbed by man they are often forced to fly beneath the hunting hawk. They are loose-feathered and easy to pluck. In every respect they are an ideal species for the peregrine to prey upon. They are noisy, conspicuous, numerous, heavy, well-fleshed, nourishing, and not hard to kill.
Black-headed gull
White gulls are the most conspicuous of all winter birds. Against dark ploughland they are visible even to the feeble human eye when half a mile away. That is why the peregrine kills so many adult gulls, and so few juveniles. Gulls can rise quickly to evade the stoop, but they are easily driven to panic by attack from below. Their whiteness blends with the sky. It may make them invisible to the fish they live on when at sea. Relying on camouflage, perhaps they are slow to adapt themselves to unexpected danger from beneath. It was once believed that peregrines detested gull-flesh. Many gulls are killed by Finnish peregrines during the summer, and gulls are frequently taken on the coast of Norway, and in Scotland.
Lapwing
They are well hidden when feeding in a field, but the flocks always fly up when a peregrine goes over. As soon as they rise, their black and white tails are a target to the falcon’s eye. Their spring display flight makes them careless of danger and less alert to predators. They have the reputation of being hard to kill, but the peregrines I have seen have outflown them fairly easily.
Wigeon
Peregrines prefer wigeon to any other species of duck. It is the commonest coastal duck, in winter, and its broad white wing-markings and loud whistling calls make it very conspicuous. Like all duck, it flies fast and straight, but it cannot dodge easily from the stoop. In March the paired birds are slow to react to the peregrine’s approach. When wildfowling finishes in February, the peregrine kills more duck and is often seen hunting on the coast at nightfall.
To summarise, these are the characteristics that make birds vulnerable to peregrine attack: white or light-coloured plumage or markings, too great a reliance on cryptic colouring, loud repetitive calling, audible wing-beats, straight inflexible flight, prolonged and high song-flight (e.g. skylark and redshank), display and fighting by males in spring, feeding too far from adequate refuge, the habitual use of the same feeding and bathing places, flying to and from roost along known ways, the failure of a flock to bunch together when attacked.
The quantity of food eaten by wild peregrines is difficult to estimate accurately. Captive peregrines are given four to five ounces of beef daily (or its equivalent). Wild juveniles probably eat more than this. A wild tiercel will kill and eat two lapwings each day, or two black-headed gulls, or one woodpigeon. A falcon may eat two woodpigeons – though not wholly – or one larger bird, such as a mallard or a curlew.
During March, a greater variety of prey is taken, including a wider range of bird species and a surprisingly large number of mammals. Moult is beginning, and the time for migration is near. An increased blood supply is needed for the growth of new feathers. The peregrine seems to be always eating. Two birds are killed daily, as well as mice, worms, and insects.
The eyes of a falcon peregrine weigh approximately one ounce each; they are larger and heavier than human eyes. If our eyes were in the same proportion to our bodies as the peregrine’s are to his, a twelve-stone man would have eyes three inches across, weighing four pounds. The whole retina of a hawk’s eye records a resolution of distant objects that is twice as acute as that of the human retina. Where the lateral and binocular visions focus, there are deep-pitted foveal areas; their numerous cells record a resolution eight times as great as ours. This means that a hawk, endlessly scanning the landscape with small abrupt turns of his head, will pick up any point of movement; by focusing upon it he can immediately make it flare up into larger, clearer view.
The peregrine’s view of the land is like the yachtsman’s view of the shore as he sails into the long estuaries. A wake of water recedes behind him, the wake of the pierced horizon glides back on either side. Like the seafarer, the peregrine lives in a pouring-away world of no attachment,