in most of East Anglia and the Midlands, and by 1900 they were only to be found in Cornwall, Wales, the Lake District and Western Scotland. By 1954 the situation had somewhat improved, and the birds had recolonised many of the areas occupied in 1865. This spread was clearly due to the decrease in game preservation during and after the 1914-18 war. If the data for buzzards and the numbers of gamekeepers are mapped side by side, this shows a good negative correlation.
To-day many gamekeepers are more enlightened. Although hawks and other carnivorous birds do eat some game birds, they prey much more on small mammals (mice, voles, etc.) which compete with game for food. Most predators are now themselves legally “preserved,” though they can be shot if caught in the act of taking poultry or game. We may see an improvement in numbers, similar to that manifested by the buzzard between 1900 and 1954, for many other species, if the new danger from agricultural chemicals can be overcome.
Smaller, non-carnivorous mammals and birds do a lot of damage, the amount of which is not always recognised. Rabbits were probably introduced into England by the Normans in the eleventh or twelfth century and were comparatively uncommon, prized as game animals until the nineteenth century. Then, for some reason which we do not yet understand, they suddenly increased in numbers so that a density of twenty animals to an acre was not uncommon, and as many as 100,000,000 carcasses were sold in a year, without noticeably depleting the numbers still at large. It was not until rabbits were wiped out in many areas by myxomatosis in 1954 that the extent of the damage they had done was recognised. Pre-myxomatosis control, by shooting and trapping, was rarely effective, and merely served to “crop” the population. The importance of myxomatosis is discussed in chapter 10.
Fig. 1 Changes in the distribution of the buzzard in the British Isles. (from Dr. N. W. Moore with acknowledgement to British Birds).
KEY: Black: Breeding proved, or good circumstantial evidence of breeding.
? on black: Circumstantial evidence suggests that breeding probably took place.
? on white: Inadequate evidence of breeding.
White: No evidence of breeding.
Fig. 2 a. The breeding population of the buzzard in 1954.
KEY: Black: 1 or more pairs per 10 square miles.
Cross-hatch: More than 1 pair per 100 square miles, but less than 1 pair per 10 square miles.
Diagonal hatch: Less than 1 pair per 100 square miles.
White: No breeding buzzards.
+ means that breeding density may belong to the category higher than that indicated.
—means that the breeding density may belong to the category lower than that indicated.
b. Game preservation in 1955.
KEY: Black: 3 to 6 gamekeepers per 100 square miles.
Cross-hatch: 1 to 2 gamekeepers per 100 square miles.
Diagonal hatch: Less than 1 gamekeeper per 100 square miles but more than 1 per 200 square miles.
White: Less than 1 gamekeeper per 200 square miles.
G. Principal grouse-preserving areas. On these, and also on some very large estates, the numbers of keepers may be higher than shown on this map.
Mice and rats invaded man’s home as soon as there was a home to invade. They also lived in his grain stores and farm buildings. Early man tried to make his granaries rodent-proof, sometimes with remarkable success. Control by trapping and poisoning was generally inefficient, and the rodent population in contact with man was roughly a measure of the amount of food he made available. A mouse-proof larder is more effective than an apparently efficient trap. The domestic cat was probably the most useful method of local control, though cats, like other “pesticides,” have had their side effects. Those that have escaped and become feral have important effects on other wild life. Modern methods of rodent control are much improved, but these animals still do much economic damage in our cities and on our farms to-day. It is perhaps surprising that the black rat (Rattus rattus), which is found mainly in towns, where it is particularly at home in hot-water ducts in tall buildings, was our “original rat,” though some think even it only arrived about A.D. 1200, and the brown rat (Rattus norvegicus), which is the species commonly found in the country, only arrived in Britain in the eighteenth century. The black rat was apparently driven from the rural haunts by the brown invader.
Pigeons and sparrows are serious agricultural pests, against which no really satisfactory control measures have so far been devised. Pigeons become more numerous each year. This increase is probably due to the increased amount of winter food, particularly clover leys on farms, that is available. The recent fall in the number of hawks may also have had some effect. Organised shoots give some sport to the participants, but have negligible effects on the pigeon population. Work on poisoning or narcotising pigeons is progressing, but the danger to other and more desirable species of birds is difficult to prevent. Sparrows probably increase because suburban householders feed them in winter. This enables them to survive in cold weather, and the increased population does more harm on the nearby farms to which it migrates in summer and autumn. Again shooting and trapping has little effect.
Farmers and others were then soon aware that wolves and other large mammals and birds might be pests, competing with them in various ways, even if they often overestimated the damage done by the carnivores and sometimes underestimated the amount of food taken by rabbits and other herbivores. They took active, if sometimes misdirected, steps to control these animals. On the other hand, they almost always underestimated the harm done to their crops and to their health by insect pests, and it is only in recent years that serious attempts have been made at control in this direction.
In Britain we do not have plagues of locusts, which in many countries can consume the whole of a crop, but it is estimated that to-day some £300,000,000’s worth of food is lost each year because of pests of crops and insect damage to farm stock. This sum is almost exactly the same as is spent annually on the support of agricultural prices (“farm subsidies”). Some insects, like the caterpillars of Cabbage White butterflies, eat crop plants, reduce the yield and make many plants unsaleable. Other insects do little damage themselves but carry organisms which cause diseases. Thus aphids carry the virus causing virus yellows in sugar beet; this can seriously reduce the value of the crop. For many years farmers and gardeners accepted insect damage as something they could not prevent. They learned by experience that it could sometimes be avoided or reduced to a minimum by timing their operations carefully. Thus if broad beans in the garden are sown early, seed is set before aphids (“black fly”) are numerous and a good crop is obtained, but in two years out of three a late sown crop will be smothered by insects and prove a failure. Cultural devices such as this are valuable and important, but will seldom allow a late crop of broad beans to be produced. Field beans, which flower and set seed over a long period during the summer, cannot be successfully grown in a way to avoid attack in a bad aphid year. Resistant strains of crop plants have been recognised and used for many years, and in future are likely to prove very important, where resistance is linked with high yield and quality. Farmers generally prefer to be able to grow the most profitable crop at the most convenient time and wish to attack pests by any possible means. Before 1939 most effective insecticides (except general poisons very dangerous to man) could only be produced in relatively small
