The population of England and Wales slowly increased from about 4 million in 1603 to 5½ million in 1714, held in check by a high death-rate. The explosion occurred with the Industrial Revolution, from 9 million in 1801 to 18 million in 1851. For a while the rate of increase was held down by a high urban mortality, through epidemics of cholera and other diseases of overcrowding. Improved hygiene in the latter half of the nineteenth century removed this check and the rate of natural increase was only halted in the 1920s (it fell from 10.4 in 1921 to 3.9 in 1931) as a direct consequence of contraception but by now there were 40 million people in England and Wales, reaching 52 million in 1959.

These demographic statistics serve two functions here. They illustrate for the human population some of the principles to be discussed in the next chapter in relation to birds. In particular, although the birth-rate was high in the seventeenth century (as it was earlier) the population was relatively stable due to a high reciprocal death-rate. Population size increased in response to improved environmental resources during the Industrial and Agrarian Revolutions. The data also emphasise the pressures that man had come to inflict on the land and, by inference, on its wild life. In the nineteenth century, bustard, bittern, avocet, ruff, black tern and roseate tern vanished, and large birds of prey like the goshawk became rare. Loss or fragmentation of their habitat was not the sole reason because some have since returned, and man’s greed must be blamed to a large extent: there were those to whom the rarity of a bird made its capture imperative.

Those people living near large colonies of nesting birds have for long been able to harvest them for food. Fisher and Peterson have related how ancient sea-fowling communities in Greenland, Iceland, the Faroes and St Kilda had evolved a rational level of exploitation of the seabird colonies of gannets, fulmars and auks, ensuring that sufficient eggs or young birds were left to prevent declines in the future harvest. By trial and error they have found that about half the auks’ eggs can be collected, as these species lay repeats, but fulmars do not and are better left alone to hatch their young. In a valuable review dealing with the exploitation of the eggs of wild birds throughout the world, Cott has emphasised how the factors governing the utilisation of wild birds’ eggs are accessibility, palatability and availability. The first two are rarely limiting, but the size and concentration of the potential crop is important. Cott found that with the exception of the eggs of certain boobies, cormorants and pelicans, which are rank and fishy to a cultivated palate, there is a broad correlation between palatability, size and colonial grouping. For reasons which will become clear in Chapter 2, most adult birds and their eggs can withstand considerable cropping without the replacement potential being adversely affected, and, as with all wild food resources, the object is to achieve the highest annual cropping rate without detriment to the maintenance of a sustained yield. In the late nineteenth century this level was exceeded in species after species, with the same thoughtless greed with which the Victorians exploited other natural resources and the colonies. In 1884, 130,000 guillemot eggs were collected from Bempton (at the time, tons of eggs were sent to Leeds where the albumen was used in the manufacture of patent leather); in 1840, 44,000 black-headed gull eggs were taken from Scoulton Mere, and 89,600 puffin’s eggs were taken from St Kilda in 1876.

The adornment of their ladies with feathers was another excuse for slaughtering wild birds. Quite apart from a scandalous trade in ostrich and egret plumes, a host of seabirds were massacred within the British Isles. Kittiwake wings were in demand for the millinery trade and a large industry existed at Clovelly in Devon and elsewhere; 9,000 are supposed to have been killed on Lundy in one fortnight. Coulson (1963) gives many other examples and relates how the species was also shot for sport and food, resulting in a decline from which it did not recover until the early decades of the twentieth century.

It is against the background of serious over-exploitation that the increase of a very wide range of seabirds in the twentieth century must be viewed and several examples will appear in later chapters – the great crested grebe (see here), kittiwake (see here), oystercatcher (see here). The eider perhaps should also be mentioned. One hundred years ago it was confined to the islands on the west coast of Scotland, and at one mainland site in East Lothian and in the Farne Islands. From this very restricted range it had spread to a wider range in coastal Scotland and to the Shetland and Orkney Islands by about 1890, and it became common by 1922. The bird has always been subject to intensive cropping both for its eggs and its down. While its down could be collected from the nest after the eggs have hatched, in the majority of cases the eggs and down have been lifted together, repeat layings often being harvested as well. On the Farne Islands the eider has always received a measure of protection owing to its association with St Cuthbert, but as long ago as 1397 the Bursar’s roll of the Monastery of Durham, which contained the Shrine of Cuthbert, mentions the use of eider-down for stuffing and cushions. Several colonies in Scotland and the Farne Islands were reduced during the 1939–45 war when the birds were collected for food, but these have recovered. In addition, Tavener has documented a marked post-war rise in numbers of non-breeders round the British coast, associated with an increase in the Dutch population, and also increases in other parts of Europe and North America, all apparently resulting from protection. There has, however, been little southward extension of the bird’s breeding range in Britain in the past 20 years. More recent studies by Dr H. Milne on the Sands of Forvie Nature Reserve, Aberdeenshire, showed that local numbers increased from about 3,000 birds in 1961–3 to around 5,000 during 1964–7 and that most of this increase resulted from a particularly good breeding season in 1963. Thus home-production rather than immigration apparently accounts for eider increases in Britain at least.

The excesses of the late nineteenth century roused the passions of a few men, and probably more women of suffragette spirit, and their campaigning led to the first Seabirds Preservation Act of 1869, hopelessly inadequate in its conception but a step in the right direction, to be followed by the Protection Acts of 1880–96. This same climate of moral indignation also led to the formation of the Society (later Royal Society) for the Protection of Birds in 1891. The Society went from strength to strength in the vanguard of the more enlightened attitude to birds characteristic of the start of the present century, doing immense good for ornithology, albeit sometimes for the wrong reasons. Today, the R.S.P.B. stands in the forefront of a scientific and imaginative approach to bird conservation.

With the outbreak of the First World War a new and widespread appreciation of birds was apparent. Birds were still used, but in an atmosphere of greater affection and regard. Canaries are about fifteen times more sensitive to poisonous gases than man, and they were accordingly kept in cages in the trenches to give advance warning of a gas attack, just as coal miners had used them in the mines. Soldiers enjoyed their companionship, and singing birds also were extensively used in ambulance trains. As pigeons had relayed the conquest of Gaul to Rome and had brought the first news of Napoleon’s defeat at Waterloo to England, so they were put to extensive use in the war, old converted London buses being used as mobile pigeon lofts. In the Second World War, pigeons were again used extensively; for example, the underground movement in France employed them to send back messages to England. German gunners tried to shoot these birds down as they crossed the Brittany cliffs, and in Britain the authorities attempted to exterminate our south coast peregrines, for fear that they too might be successful in intercepting some vital message. The following appeared in The Times on 19 August, 1943:

A pigeon, released by a bomber crew from their rubber dinghy, has recently been responsible for their rescue in the Mediterranean. … Realizing that something had gone wrong when there was no response to their first S.O.S., they had released their carrier pigeon from its container. As soon as the message it carried had been deciphered, an air-sea rescue launch put out, and the airmen were safely rescued.

In contrast with a report for 26 September, 1969:

‘In what was called “the craziest strike of all”, 44 men went on strike for half a day at the giant pressed steel Fisher Body plant in Swindon because of low-flying pigeons. The dispute was the latest of a series of labour stoppages which is costing Britain’s car industry the loss of millions of pounds in exports. The workers who walked out were those who were caught in the crossfire of the “feeders”, men who have been scattering bread crumbs and other bits of food to encourage the pigeons, and the “whangers”, other workers who have been throwing nuts and bolts and other missiles to scare the birds away. “We were fed up with either being hit by nuts and bolts aimed by the whangers, or strafed by the pigeons diving for food,” a press operator said. Meanwhile, a works management committee has asked the “whangers” to stop throwing missiles and the “feeders” to eat their sandwiches themselves.’

Some of the major developments in the relationships between men and birds since these years have been very briefly mentioned in the preface, but much more could be added for which there is no space. It would be pertinent to follow the growth of pet-keeping and other manifestations of an increasing public interest in living things. Similarly, we might examine the post-war boom in bird watching and the significance of such discoveries as the number of rare birds visiting sewage farms; the stampede to such sites was like an ornithological ‘gold rush’ once the initial discoveries at Nottingham were disclosed (Staton 1943). Has this widespread interest in wild life come too late?

The main hazards to birds today arise from the increasing pollution of the environment with the waste resulting from the sheer numbers of man; ironically man has become an indirect threat to the survival of wild life just when he seems to have learned to appreciate it. Mellanby has recently dealt with the pollution problem so admirably that I shall not attempt more than a passing reference here. But this should not detract from the severity of problems about which new facts emerge almost daily. For instance, we are still treading extremely cautiously so far as certain persistent agricultural chemicals are concerned. When the threat to wild life from organochlorine insecticides became really apparent in 1960–1, there was all manner of special pleading; agriculturalists claimed that food production must be the over-riding concern, manufacturers of chemicals naturally enough belittled the hazards to birds, bird protectionists made exaggerated claims, and Rachel Carson did the public at large a service with her deliberately biased book. In the years that have followed the initial hysteria, good sense has prevailed. Research has got under way and is producing facts where before there was only conjecture. When bird watchers first pointed out that birds of prey were breaking and eating their eggs and that this seemed to be associated with the decline in numbers associated with toxic chemicals, their suggestion was greeted with scepticism by many people. Now, a careful study by Ratcliffe has suggested some answers, for he has demonstrated that there has been a decline in egg-shell thickness in the peregrine, sparrowhawk and golden eagle since about 1950, and this explains why eggs are broken more readily and are subsequently eaten by the parent birds. Thus, of 109 peregrine eyries examined between 1904–50 there were only three instances of egg breakage, compared with 47 in 168 eyries observed between 1951–66. Egg-breakage, decrease in egg-shell weight, status of the breeding population and exposure to persistent pesticides are correlated, and it would be unreasonable to suppose that there is no causal connection, even if the exact factors and mechanisms involved remain to be elucidated. Calcium metabolism in birds is controlled by oestrogen and parathyroid hormone, and there is evidence that pp D.D.T. will interfere with oestrogen-based mechanisms in the Bengalese finch (Jefferies 1967).

Pollution of the environment by persistent, poisonous chemicals, is the most obvious problem, firstly because small residues can be accumulated in food chains, to give lethal dosages to the top predators, and secondly because they may produce unsuspected side-effects. But pollution by detergents, oil, smoke and other waste from man also present grave problems. Oil spillage at sea, either accidental or resulting from the purposeful jettisoning, is a serious hazard to seabirds against which the International Committee for Bird Preservation and other bodies have long campaigned, to a large extent successfully in the sense that the problem is recognised internationally. Bourne (1968), in a valuable review of the subject, mentions that as long ago as 1907 the largest seven-masted schooner built, the Thomas W. Lawson, was wrecked on the Isles of Scilly on her maiden voyage. The release of her entire cargo of ‘two million gallons’ of crude oil caused a vast slaughter of local seabirds, particularly puffins. In those days Annet is supposed to have supported about 100,000 puffins, whereas to-day only about 100 remain. All the colonies in the Western Approaches have been similarly reduced (as Parslow 1967 has shown) and it seems likely that oil pollution has been a major cause.

The loss at sea of oil-carrying vessels during the 1914–18 war resulted in a large increase in the numbers of oiled seabirds. This led the Royal Society for the Protection of Birds to publish figures in 1921 which played a large part in the introduction of the ‘Oil in Navigable Waters Act’ soon after. In the Second World War most tankers carried petroleum spirits, and the destruction of shipping presented less hazard. But this situation has changed as the needs of a modern industrialised world have led to an enormous expansion in oil traffic at sea; nowadays crude oil is carried to refinement plants near the destination in giant tankers. Constant pollution arises from ships washing-out at sea after a voyage and purposely releasing oil, while occasional accidents can have widescale repercussions. Thus, during the night of 18 September, 1966, the German tanker Seestern allowed 1,700 tons of crude diesel oil to escape into the Medway Estuary on a flood tide, polluting 8,000 acres of saltings. Probably about 5,000 birds died immediately. Certainly, 936 black-headed gulls, 927 great black-backed gulls, 184 dunlin, 165 herring gulls, 135 redshank, 98 common gulls, 90 oystercatchers, 65 curlew and various other birds (including an American pectoral sandpiper) were picked up. In this case the number of birds using the area had declined, by 20–100% depending on the species, in the following winter, but has since recovered so possibly no permanent damage has been done, yet for years an area could be denuded of suitable plant and animal food for birds and other wildlife. Only a small oil slick of about 87 tons hit the Tay estuary, the most important wintering ground for eiders, in March 1968. Fortunately, most of the birds had left, but between 7–26% of the national eider population was wiped out: the happy state of affairs pertaining to eiders and described above could soon be reversed. These modern incidents compare with R.S.P.B. estimates made for the 1940s and 50s that between 50,000–250,000 birds were being killed per year in home waters.

On 18 March, 1967, the Torrey Canyon ran on to the Seven Stones Reef and in all about 60,000 tons of crude oil were lost into the sea. At least 10,000 birds were collected, and many more must have died unbeknown, of which 9 out of 10 were guillemots. In the aftermath we now know (see special review by Bourne 1970, and Parslow 1967) that guillemots at some breeding colonies in Scilly and the north Cornish coast have been considerably reduced; in Cornwall, but not Scilly, fewer shags and herring gulls were breeding in 1966; kittiwake numbers at a colony within the worst polluted area were reduced in 1966. Only a few razorbills and apparently no puffins suffered in Britain, though these last are difficult to census. This was not the case in the Sept Iles in Britanny, the most important seabird colony in France, where careful protection had allowed a recovery in seabird numbers following the persecutions of the last century. While aerial species such as the gannet had escaped damage, such divers as the shag had suffered markedly and the auks very severely: counts before and after the incident show that the number of pairs of guillemots fell from 270 to 50, of razorbills from 450 to 50, and of puffins from 2,500 to 400. This is the first incident where really detailed knowledge has been available, making a fairly comprehensive ecological survey possible so that wildlife interests are given more than passing regard. The public has been aroused at the prospects of ruined beaches and the ‘overriding concern of the Government throughout has been to preserve the coasts from oil pollution and to adopt a course most likely to achieve this end’. Unfortunately the enormous quantities of detergents used for this purpose have done vastly more immediate and probably long-term harm to intertidal organisms than the oil itself. Whatever the pros and cons of the whole sad story, it illustrates the dilemma man finds himself in today. In some fields his technology has progressed far too quickly, while in others it has lagged, so that when accidents occur he is too often forced to resort to ill-conceived panic measures. Since this book has been in press there has been another major wreck of auks, this time in the Irish Sea in August 1969. At first attributed to gales, it seems that many birds came ashore under conditions of not particularly unfavourable weather. Analyses show the bodies to contain high levels of polychlorinated biphenyls, agents used in the paints and plastics industry. This new chemical hazard, unrealised when Mellanby prepared his book, highlights the complexity of the interaction of man and wildlife and the need for drastic measures if man is to avoid becoming the ultimate victim of this extensive environmental pollution, which wildlife is indicating.

CHAPTER 2

ECOLOGICAL CONSIDERATIONS

A THOROUGH insight into the relationships between birds and humans demands some understanding of population ecology, a knowledge of how animal numbers fluctuate and change through births and deaths and of the factors which determine these processes. Populations have dynamic properties and these cannot be neglected by people concerned with wild life management, whether as game preservers, conservationists, pest controllers or farmers. This chapter attempts to set out some of the basic principles with pertinent examples, but these same principles will emerge in later sections in various guises. Our knowledge of the subject was first collated and clearly enumerated by Dr D. Lack (1954) in a stimulating book The Natural Regulation of Animal Numbers since when more field studies have been made by various workers, which Lack (1966) has summarised in his Population Studies of Birds. Both books should be consulted by the reader who is really interested in this subject. In this account I have drawn on examples which, wherever possible, have direct relevance to economic ornithology.

Farmers tend to the pessimistic belief that all problem birds become more abundant every year. Yet careful counts of most such species living in stable environments usually show there to be no clear tendency towards a steady increase, or even decrease, though numbers may fluctuate from year to year. For instance, many farmers believe that the wood-pigeon has increased drastically during this century to become more of a pest, though in conditions of stable agriculture this is unlikely to be true. In fact, there is evidence of a decline since the early 1960s associated with a reduction in the acreage of winter clover-leys and pastures. Certainly the species has moved into newly developed marginal land; places like the east Suffolk heathlands, which have been ploughed and claimed for agriculture since the Second World War, have been colonised by wood-pigeons. Fig. 1 gives some indication of how wood-pigeon numbers have varied on a Scottish estate near Dundee since 1887, and it is evident that fluctuations have occurred within narrow limits, with no evidence at all for a sustained rise or fall. In contrast, Fig. 1 also shows how the closely related stock dove has increased over the same period; this species first colonised in Scotland in 1866, reached Fife in 1878 and increased dramatically in Scotland in the next ten years. Every year each pair of wood-pigeons rears on average just over two young and it is evident that if all these survived to breed in their turn, population size would increase exponentially. That this does not normally occur indicates that some form of regulatory mechanism must be operating. Furthermore, this regulation must be density-dependent, that is, it must become proportionately more effective at high population densities and proportionately less effective at low ones. If the regulatory factor (s) operated without regard to density, it is evident that population size could fluctuate widely without reference to a particular level – to the constant mean represented by the dotted line in the figure.

FIG. 1. Annual number of wood-pigeons and stock doves shot on an estate near Dundee. The data refer to an area which remained virtually unchanged during the period under review, and nearly all the birds were shot by one man who maintained a reasonably constant shooting pressure. They, therefore, probably provide a fair index of the total population. The autumn of 1909 was a disastrous one for the harvest owing to gales and rain from August until October so that much corn remained uncut. This resulted in an influx of wood-pigeons and the appearance of stock doves in large numbers. (Data by courtesy of Dr J. Berry.)

FIG. 2. Logarithmic increase of the collared dove in Britain. (Data from Hudson 1965).

Sometimes bird numbers do in fact increase geometrically, as when a species moves into a previously untenanted region where there is scope for it to live; in biological terms where a vacant niche exists (see below). In this way the collared dove dispersed dramatically across Europe to reach Britain in 1952. It had spread to south-east Europe from northern India by the sixteenth century but had then remained static in its European outpost until 1930. It has subsequently spread north-west across Europe, reaching Jutland in 1950 and Britain in 1955; an expansion 1,000 miles across Europe in twenty-four years. Why this spread was so long delayed is not clear, though it is most feasible, as Mayr has suggested, that a genetical mutation occurred which suddenly rendered the species less restricted in its needs. (We can imagine a bird, though not necessarily the collared dove, to be restricted by a temperature tolerance which a single sudden genetic mutation could remedy.) Throughout Britain and Europe a vacant niche existed for a small dove living close to man; it is even possible that the decline in popularity of the dove-cote pigeon created this niche. Whatever the explanation, a high survival rate among collared doves has evidently been possible, and their potential capacity for geometric increase has been realised: see Fig. 2, which relates to Britain. The Syrian woodpecker may be on the brink of a similar explosion. It is considered to be a recently evolved species (post-glacial) which replaces the great spotted woodpecker in south-east Asia. It spread to Bulgaria to breed in 1890, to Hungary in 1949 and to Vienna in 1951. A significant feature of the bird’s ecology in Europe is its confinement to cultivated areas which do not suit the great spotted woodpecker. If it proves to be better adapted to this man-made niche we can anticipate a continuing advance across Europe. Agricultural development in the Balkans may well bring other surprising range extensions.

Accepting* that populations are controlled in a density-dependent manner the next question to consider is the nature of these regulatory processes. Fundamentally, either the birth-rate or death-rate must be the factor of change. Wynne-Edwards and his supporters have argued that the reproductive rate is of much importance and that those animals with a high expectation of survival, such as many seabirds, have evolved low reproductive rates and vice versa. They have also claimed that a host of conventional behaviours have evolved as a means of regulating numbers. For instance, Wynne-Edwards regards the eating of eggs and young, practised by many raptors and also storks, as a device to limit their reproductive output; deferred maturity (gulls do not breed until three or four years old), territory formation, and various other behaviours are similarly regarded in this light. These views form part of his more general thesis that animal numbers in undisturbed habitats are at an optimum density and that maintaining this optimum has selective advantages. Special cases of this theme have attracted various supporters. E. M. Nicholson (1955) is one and he ascribes population control to density-dependent movements, rather than to mortality, while Lidiker (1962) goes further in seeing emigration as a mechanism enabling populations to have densities below the optimum carrying capacity of their habitat. Hence, Wynne-Edwards regards behaviours such as those listed above as homeostatic (self-regulatory) mechanisms, being induced by the population rather than by the environment.

Wynne-Edwards also drew parallels between bird and human populations, claiming that infanticide, taboos and other methods of reproductive restraint practised by so-called primitive societies were extensions of these same deep-rooted animal behaviours. In so doing he resuscitated some very early ideas of Carr-Saunders (published in 1922) which the well-known demographer did not subsequently repeat. Indeed, Mary Douglas, in criticising the idea of an optimum population, points out that there are many examples of human under-population. Considering certain primitive societies in detail, she makes it clear that they represent highly evolved and complex groups about which generalisations are meaningless. For instance, the Netsilik Eskimos live in a harsh environment where males suffer a very heavy mortality in hunting, and female infanticide is practised primarily to maintain an even sex balance. The Ndembu, a Lunda tribe in Zambia, grow cassava as their staple crop and live at a density of 3–5 people per square mile, whereas cassava could support a density of 18 people per square mile. The reason for the discrepancy is that the tribe passionately love hunting and move their villages to where game is available so that they never reach a stage where they are up against the ceiling imposed by their basic resources. As Douglas says: ‘they live for the oysters and champagne of life not the bread and butter.’ On the other hand, the Rendille are a tribe of camel herders in Kenya and live on the meat and milk of their sheep and camel herds. An optimum number of people is needed to maintain the camel herd, and when smallpox reduced man-power, stock had to be lost. In more normal conditions a balance of man-power is achieved by emigration, monogamy (herds are not divided but go only to the eldest son), while a measure of infanticide is practised (all boys born on Wednesdays).

In general terms, homeostatic population control in human groups depends on limited social advantages (the enjoyment of hunting by the Ndembu; education, motor cars and social prestige in western Europe) and not on any relationship to resources per se, as is the case with infra human species. Douglas could well be right in not attributing the increase in the Irish population between 1780–1840 to the adoption of potatoes as a staple diet, but rather to the ruination of Irish society by penal laws and English trade tariffs. Similarly she argues that the miseries of enclosures and the Poor Laws resulted in the population explosion which led to the Industrial Revolution, rather than that increased resources stimulated an increase in population. If true, this is quite different from the way in which animal populations are determined.

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