Toxic chemicals and birds of prey

Transcription

1 Toxic chemicals and birds of prey By Stanley Cramp INTRODUCTION THE DRASTIC DECLINE in the numbers of almost all our birds of prey in the 9th and early 20th centuries, due to the increased efficiency of fire-arms, to collecting and, above all, to the spread of game preservation, was followed in the cases of most of them by a general improvement in status which lasted until about the middle of the 950's. In this, protection, the slow spread of a more enlightened attitude and the reduced activity of gamekeepers, especially during the two World Wars, all played a part. In the last few years, however, there have again been reports of declining numbers of some species, at a time when the growing use of toxic chemicals in agriculture and horticulture has provided a new threat to many forms of wild life. It is continued... 24

2 TOXIC CHEMICALS AND BIRDS OF PREY tempting to assume that the one has led to the other, but can this, in fact, be established? This paper examines the available evidence, much of it recent. RECENT CHANGES IN NUMBERS OF BIRDS OF PREY There are, unfortunately, all too few accurate census figures for any species of birds, either before or since the new synthetic pesticides began to be used on a large scale, and this applies to most of our birds of prey, both diurnal and nocturnal. The most recent assessment was made in 957 (Brit. Birds, 50: 29-55, 73-97) and it dealt only with the rarer diurnal birds of prey, without attempting to cover the positions of the owls or the three commoner raptors the Sparrowhawk, Merlin and Kestrel.* It was in the cases of two of these, the Kestrel and the Sparrowhawk, that signs of a widespread decline in numbers in recent years were first noted. After the i960 breeding season, R. S. R. Fitter, on behalf of the Council for Nature, gathered information from observers in a number of counties in England and Wales. The results showed evidence of a fall in the numbers of Kestrels in Northumberland, Yorkshire, Lincolnshire, Nottinghamshire, Norfolk (except for marsh areas and the Broads), Suffolk, Cambridgeshire (except for the Fen Washes), Huntingdonshire, Essex and Oxfordshire, with little apparent change in Hampshire, Wiltshire, Dorset, Montgomeryshire, Merionethshire, Flint, Lancashire, Cumberland, Derbyshire and Leicestershire. The Sparrowhawk appeared to have been still worse hit, with decreases in Northumberland, Yorkshire, Lincolnshire, Derbyshire, Leicestershire, Norfolk, Suffolk, Huntingdonshire, Essex, Oxfordshire, Hampshire, Dorset and Montgomeryshire, only Pembrokeshire and Flintshire reporting no evidence of any recent changes in numbers. Thus R. S, R. Fitter's information showed that both species had declined, often markedly, in the south and east of England and that in the case of the Sparrowhawk this decline extended also to parts of western England and Wales. An examination of the county bird reports for i960, and, where available, for 96, confirms this general picture, except that in Yorkshire the Kestrel seems to have decreased in only parts of the county. In addition, the reports show that the Kestrel has now declined in Kent and probably Leicestershire, but not apparently in Herefordshire; and that the Sparrowhawk has now decreased in Herefordshire, Nottinghamshire and the London area, but not in the Bristol area. They also suggest that the Sparrowhawk may now be virtually extinct in Lincolnshire, Huntingdonshire and Norfolk. Some light on the timing and extent of this decline is provided by *The scientific names of all birds mentioned in the text can be found in the appendix on page 39; other-wise they are given only in the tables. 25

3 BRITISH BIRDS an analysis of the Nest Record Cards for these two species, which has kindly been made by Henry Mayer-Gross, of the British Trust for Ornithology (fig. i). The numbers of cards relating each year to nests of Kestrel and Sparrowhawk are very small and therefore liable to be influenced by chance fluctuations, but the general picture is clear and agrees closely with that drawn from the reports of observers. Whilst the total of Nest Record Cards for all species rose from about 5,000 in 950 to between 8,000 and,000 in the years 95 to i960, with a sharp rise to over 4,000 in 96, the number of Sparrowhawk nests reported under the scheme showed signs of a general decline from about 955, most marked in eastern and southern England, but affecting the rest of Great Britain from 957 onwards. The decline of the Kestrel is less marked on the Nest Record Cards, and so far appears to be largely confined to southern and eastern England, where it seems to have begun about 956. In the case of a much rarer species, the Peregrine, we have far more exact data to show a recent and almost catastrophic fall in numbers. At the request of the Nature Conservancy, a census of Peregrines was organised by the British Trust for Ornithology in 96 and 962. This followed representations by the pigeon racing enthusiasts, who feared that these falcons were a serious threat to their birds, but it now appears that the problem is not one of regulation of numbers of the Peregrine but rather the conservation of the remnants of a seriously threatened species. In 96, 43 of the 78 Peregrine territories known in Great Britain were visited. In southern England and Wales the majority of nesting places appeared to be quite deserted, and only eleven pairs in the 56 sites visited were known to have reared young. In northern England and southern Scotland, Peregrines were entirely absent from 45 of the 97 territories visited and only eleven pairs were known to have reared young. In the highlands and islands of Scotland the picture varied from district to district; some areas had a fairly normal nesting season, with most territories occupied and most pairs succeeding in hatching eggs, but in others (including some of the remotest) a much lower proportion of breeding pairs produced young, although the nesting populations were normal. Taking the country as a whole, of the 43 territories visited, Peregrines were absent from 73, one or both birds were present but not known to nest in 8, and of the remaining 40, where eggs were laid, only 82 pairs were known to have reared young. The general picture, with this trend of deterioration northwards, was similar in 962, but there was evidence of a further decline, particularly in regions south of the Highlands, where breeding success was only half that of 96. The 962 results indicated that about half the pre- 939 population of Peregrines in Great Britain, about 650 breeding 26

4 TOXIC CHEMICALS AND BIRDS OF PREY FIG. I. Numbers of B.T.O. Nest Record Cards for the Sparrowhawk (Accipiter nisus) and Kestrel (Falco tinmmculus), 950-6, to show differences in trends between south and east England and the rest of Britain. The grand totals for all species are also shown to demonstrate that, whereas numbers of Sparrowhawk and Kestrel cards are falling, at least in south-east England, an increasing amount of attention is actually being paid to this method of recording nest data 27

5 BRITISH BIRDS pairs, had gone, and that only just over a quarter of the remainder bred successfully (D. A. Ratcliffe in litt.). There is no published information on recent changes in total numbers of other diurnal birds of prey in the British Isles, but observations made by Ash (i960) on a game preserve in Hampshire from 952 to 959 suggest that several other species may be affected. Ash's records of sightings of eight different species were made throughout the year and do not therefore refer only to the breeding populations. They show: Kestrel, a decrease from 956; Buzzard, a decline after the advent of myxomatosis in 954, then a revival, and then another decline; Sparrowhawk, a steady decline from 953; Hen Harrier, a decrease by two-thirds from 956; Merlin, a decrease by two-thirds between 953 and 957, then numbers remaining steady; Peregrine, almost a two-thirds decrease, the main decline starting in 956; Hobby, fluctuating numbers, but generally a decrease of about twothirds; and Montagu's Harrier, the only increase (in 958 and 959). Moreover, the recent decline in numbers of birds of prey is not confined to the British Isles. Ratcliffe and Moore (962) stated that they had received reports of serious decreases in Peregrines from the eastern United States, Germany, Finland and Sweden. At least in certain parts of its range in North America, the Bald Eagle has suffered severely. According to Carson (962), in the years Charles Broley used annually to ring about 50 young Bald Eagles in about 25 nests on a stretch of the western coast of Florida. In 947 the numbers of young began to decline; some nests contained no eggs and others had eggs which failed to hatch. Between 952 and 957 about 80% of the nests failed to produce young. In 957 Broley found only 43 occupied nests, of which seven produced young, and in 958 only ten nests and a single chick. At Hawk Mountain, in south-eastern Pennsylvania, the proportion of first-year eagles seen on autumn migration fell from 40% in to 20% in In the case of the nocturnal birds of prey it is more difficult, and perhaps impossible, to make any accurate assessment of total populations. There is no firm evidence of recent changes in numbers, although, as described below, owls appear to be dying from toxic chemicals on a considerable scale. EVIDENCE OF DEATHS OF BIRDS OF PREY FROM TOXIC CHEMICALS Since i960 the Joint Committee of the British Trust for Ornithology and the Royal Society for the Protection of Birds on Toxic Chemicals has, in co-operation with the Game Research Association, been collecting evidence of birds killed by toxic chemicals. Their first three reports (Cramp and Conder 96; Cramp, Conder and Ash 962 and 28

6 TOXIC CHEMICALS AND BIRDS OF PREY 963) show that 72 deaths of diurnal and nocturnal birds of prey analysed during were apparently due to toxic chemicals. These are summarised in table. Table. Reported deaths of birds of prey apparently due to toxic chemicals, British Isles, i Buzzard (Buteo buteo) Sparrowhawk (Accipittr nisus) Kestrel (Falco tinnunculus) Barn Owl (Tyto alba) Little Owl (Athene noctud) Tawny Owl (Strix aluco) Long-eared Owl (Asio otus) Unidentified owls The figures in table cannot necessarily be taken as reflecting the actual scale of deaths in each year, as it is possible that increased publicity led to more observers being on the alert for casualties in 96 and 962. On the other hand, it is also likely that for some if not all of the species the total populations, and therefore the numbers at risk, were diminishing over the period. In 96 it was possible to obtain more definite evidence on the causes of death when a number of bodies of birds of prey were sent to a London firm of public analysts and consulting chemists for chemical examination. The results are given in table z; it should be noted that at this time the methods of analysis allowed the amounts of organic chlorine to be determined, but not the identification of the specific chlorinated hydrocarbon involved. Table 2. Quantities of toxic chemicals (parts per million) found in predators in analyses sponsored by the R.S.P.B. in i96r No. of bodies Max. Mercury Organic chlorine Min. Average Max. Min. Average Sparrowhawk (Accipifer nisus) Kestrel (Fa/co tinnunculus) Tawny Owl (Strix aluco) Long-eared Owl (Asio otus) * 2* 3* *One specimen in each case not examined for organic chlorine I29

7 BRITISH BIRDS In 962, however, more refined and more expensive techniques made it possible for the specific chlorinated hydrocarbon concerned to be identified in most instances, and more bodies were analysed. I am grateful to P. J. Conder for generously supplying the details summarised in table 3. Table 3. Quantities of toxic chemicals (parts per million) found in predators in analyses sponsored by the R.S.P.B. in 962 County No. of Organic bodies Mercury chlorine Aldrin Dieldrin BHC Heptachlor epoxide Buzzard {Buteo buteo) Leics Sparrowhawk {Aaipiter nisus) Dorset Kestrel (Falcotimumculus) Lanes Little Owl {Athene noctua) Barn Owl (Ty/o alba) Tawny Owl (S/rix alucd) Lines Wilts Berwicks Ireland Kent Lines Notts Northants Beds Berks Bucks Cornwall Essex Kent Scotland Norfolk London Kent 2! I.I I.I i i present present I.I Details have also been published (Ratcliffe and Moore 962) of the results of analyses carried out by the Pest Infestation Division of the Ministry of Agriculture, Fisheries and Food. They concern some predators found dead in the spring of 962 and details are given in table 4. In the United States studies have been made to test whether there is any connection between the striking decline in the numbers of the Bald Eagle, described earlier, and the use of chlorinated hydrocarbons, such as DDT to control the salt marsh mosquito on the marshes and 30

8 TOXIC CHEMICALS AND BIRDS OF PREY coastal areas of Florida where the eagles forage for food. In an interim report DeWitt and Buckley (962) stated that of 27 field specimens of eagles analysed (two Golden and 25 Bald) all but one, a Bald Eagle from Alaska, contained measurable amounts of DDT or its metabolites. The residues contained in tissues from these birds were: liver, 0.0 to 53. parts per million (average 7.4); kidneys, 0.0 to 58.6 (average 3.6); heart, less than 0.5 to 44.0 (average 9.3); brain 0.0 to 7.5 (average 4.4); breast muscle, 0.2 to 23.4 (average 6.0). Table 4. Quantities of insecticides (parts per million) found in predators by the Ministry of Agriculture, Fisheries and Food in spring 962 Heptachlor epoxide Flesh Liver Dieldrin Flesh Liver Gamma Flesh BHC Liver Kestrels (Fako linnunculus) (a) (b) Unidentified owl In Sweden, analyses have shown the following birds of prey to contain pesticide residues: a Merlin (aldrin or mercurial fungicides), one each of Golden Eagle and White-tailed Eagle (minor amounts of mercurial fungicides), and two Eagle Owls (aldrin or mercurial fungicides; thallium sulphate rodenticide) (K. Curry-Lindahl, in Hit.). Finally, amongst the casualties in Holland in i960 following the use of parathion (an organo-phosphorus pesticide) were Buzzard, Sparrowhawk, Goshawk, Marsh Harrier, Montagu's Harrier, Peregrine, Merlin, Kestrel, Barn Owl, Little Owl, Tawny Owl and Long-eared Owl (Morzer Bruijns 962). There is abundant evidence, therefore, that many species of birds of prey in several different countries have been found dead in circumstances suggesting that toxic chemicals were the cause, and analyses here, in Sweden and the United States have shown varying amounts of poisons, mainly chlorinated hydrocarbons and mercury, in their tissues. They must have derived these poisons from their prey, as few birds of prey are likely to feed directly on dressed grain or sprayed crops. This underlines the fact that the chlorinated hydrocarbons, unlike the organo-phosphorus compounds, are highly persistent and pass readily from one organism in the food chain to another, often concentrating in the process. Perhaps the best known example is that of the Western Grebes of Clear Lake, California, which were killed by DDD applied to destroy a small, non-bloodsucking gnat. The DDD was used with extreme care, so as to cause the minimum harm to fish, and the greatest concentration applied at any one time 3

9 BRITISH BIRDS (there were three applications in all) was one-fiftieth part per million. Yet the poison built up, reaching about 5 parts per million in the plankton organisms, from 40 to 300 parts per million in plant-eating fishes, and,600 parts per million in the fatty tissues of the grebes. In a similar way, hawks and owls obtain poison from their prey. This has been shown experimentally by Bernard (962) in the United States. He fed House Sparrows with DDT, less than 200 gm. in all, and then fed parts of the sparrows to an American Sparrowhawk (the New World equivalent of the European Kestrel). The hawk died five days later in tremors, and residues of DDT were found in its organs 85 p.p.m. in the brain, 76 p.p.m. in the breast muscle, 97 p.p.m. in the heart and 22 p.p.m. in the liver. So far as I am aware, the lethal dose of the various toxic chemicals for the different species of birds of prey in this country has not been determined. This dose varies considerably, not only among different species of animals, but among different individuals of the same species. As little as 3.3 p.p.m. of aldrin or 5.8 p.p.m. of dieldrin can be lethal to adult Bob-white Quail (DeWitt 956), while, according to evidence quoted by Murton and Vizoso (in press), the LD 50 dose for feral pigeons is 67 p.p.m. for dieldrin, 55 p.p.m. for aldrin and 67 p.p.m. for heptachlor. DeWitt and Buckley (962) fed captive Bald Eagles on diets containing 0 p.p.m. and upwards of DDT. One fed at 0 p.p.m. escaped but another died, whilst all those fed at higher levels of DDT (except for one sacrificed after being fed for 2 days on a 60 p.p.m. diet) died after developing severe tremors. Some of the birds of prey analysed in Britain (tables 2-4) may have been carrying less than lethal doses of poisons and may actually have died from other causes; others almost certainly died from the pesticides they had accumulated indirectly from their prey. Also, as tables 3 and 4 make clear, a number of specimens were found to contain more than one poison and there is some evidence that in certain cases one poison may increase the toxicity of another. THE EFFECT OF SUB-LETHAL DOSES ON FERTILITY Sub-lethal doses of poisons can also have disastrous effects. DeWitt (955, 956) and Rudd and Genelly (956) showed, in the case of Bob-white Quail and Pheasants that chlorinated hydrocarbons in doses too small to kill the parent birds could seriously affect their fertility by reducing egg production, the percentage of fertile eggs and chick survival. There seems to be little doubt that some birds of prey are being similarly affected. Thus, one of the striking features of the Peregrine survey was the large proportion of pairs occupying sites and not breeding, or else nesting unsuccessfully. This was also found by 52

10 TOXIC CHEMICALS AND BIRDS OF PREY Treleaven (96) in his study of Cornish eyries. The numbers of Peregrines in Cornwall recovered well after the campaign waged against them by the Air Ministry during the war, and by 955 there were 7 pairs compared with about 20 in the 930's. But by 958 only seven eyries were occupied and only two produced young, and by i960 only three sites were occupied by ist June and only one produced young. In the United States, the decline in the fertility of the Bald Eagle has already been described; even more striking is the fate of a colony of 62 Osprey nests near the mouth of the Connecticut River, where only a single chick was reared in 962, all the other pairs having had addled eggs (R. T. Peterson per G, Waterston). Little is known of reduced fertility in other species of raptor. The Nest Record Cards for Kestrel and Sparrowhawk have been analysed by Henry Mayer-Gross to see whether they reveal any evidence of a recent decline (table 5). The numbers are too small for the Sparrowhawk for any significant conclusions to be drawn. In the case of the Kestrel, where a larger sample is available for recent years, the figures cannot be pressed too far, but they do not lend any support to a marked decline in fertility. More evidence is badly needed on this point. Table 5. Hatching and fledging success (excluding losses from predation) of Spairowhawk (Accipiter nisus) and Kestrel (Fako tinntmculus) South and east England Rest of Great Britain Eggs Hatched h Young Reared % Eggs Hatched % Young Reared % SPARROWHAWK % 2 (75%) % (00%) % 74% % (00%) KESTREL } % 57 87% % 00% 53» *% 99% % 9% For the Peregrine, Bald Eagle and Osprey, however, there is clear evidence of a high level of infertility, in circumstances suggesting that toxic chemicals might be responsible. The next step is to establish if chemicals are present in the addled eggs of these birds, and this has recently been done for all three species. Moore and RatclifFe (962) have described how an addled egg from a Perthshire eyrie was found to contain DDE (a metabolite of DDT), dieldrin, heptachlor epoxide (a metabolite of heptachlor) and smaller quantities of heptachlor and gamma-bhc, amounting to a total of between 4 and 5 p.p.m. of chlorinated hydrocarbon residue. DeWitt and Buckley (962) analysed eggs of Bald Eagles from unsuccessful nests in New Jersey, 33

11 BRITISH BIRDS and found that they contained 24.3 p.p.m.,.4 p.p.m. and 36.9 p.p.m. of DDT respectively, and three Osprey's eggs from the ill-fated Connecticut River colony were found to contain 36 to 4 micrograms of DDE and 79 to 34 micrograms of DDD (Peter L. Ames per Roland C. Clement). Finally, an addled egg from a Montagu's Harrier nest in Wales in 962 has been found to contain both DDE and dieldrin (N. W. Moore in lift.). DISCUSSION In Great Britain, therefore, there is definite evidence that the Peregrine population has declined in recent years and there are marked, though less precise, indications that the Kestrel and Sparrowhawk have also suffered. It is not known whether the total populations of other diurnal birds of prey or of owls have been affected, though there is a clear suggestion from field observations in Hampshire that other raptors began to diminish there in the mid-i 9 5 o's. Three of our diurnal birds of prey and four of our owls have been found dead in circumstances suggesting toxic chemicals as a cause, and three species of each have been shown on analysis to contain pesticide residues. Eggs of two diurnal species have been found to contain residues, and the fertility of one of these is known to have declined. Similar evidence has also been obtained for other species abroad, especially in the United States. The evidence for a link between the recent declines in some of our predators and the growing use of toxic chemicals is strong. However, Moore (962) has stressed that there are a number of other factors which may have been acting on bird populations in recent years. They include increased motor traffic, hedgerow destruction, overhead wires, myxomatosis (in 953), the post-war rise in game preservation, and the reduction in numbers (and to some extent variety) of weed-plants and their accompanying insect fauna. The precise effects of these, and possibly other factors, on the populations of different species is not known (see, however, Moore 957 for the effect of myxomatosis on the numbers and ecology of the Buzzard), although it seems obvious that, for example, the widespread habitat changes in eastern England and the reduced supplies of weed-seed and insect food could affect certain birds considerably. Even deaths from poisoning on a sizeable scale do not necessarily reduce the population of a species permanently. Thus Murton and Vizoso (in press) show that after a kill of at least 8% of the Woodpigeons in one area of Cambridgeshire in 96, the population had recovered by the 962 breeding season, when deaths of Woodpigeons from seed-dressings had been virtually abolished there after the voluntary ban on the more toxic seed-dressings had come into operation from January

12 TOXIC CHEMICALS AND BIRDS OF PREY Two considerations suggest, however, that the influence of toxic chemicals on our birds of prey has been considerable. The first is the geographical distribution of the decline. Fig. 2 shows the number of incidents of mortality due to toxic agricultural chemicals (seeddressings and sprays) in each county in 96. This is influenced to some extent by the distribution of observers, but the general picture is in striking agreement with that provided by the analysis of crops and the use of pesticides in Great Britain in 96 made by Moore (962). This may be summarised as follows (the letters S, M and E indicating that crops are grown extensively in the areas concerned): Crop % treated annually Principal areas where crops grown with pesticides North West South Midlands East Cereals 80% E. Scotland Hants Berks M E Fruit 9 %. S Worcs E Vegetables, sugar beet, stock foods 20-60% Lanes S M E Moore also stated that other crops (grass, rough grazing and timber) were subject to only limited treatment by pesticides in 96 (under 5%) and that, among these, the chlorinated hydrocarbons were used only on timber. From both these sources (Moore and fig. 2), it appears that the heaviest use of pesticides was in southern and eastern England and the Midlands, with more limited use in northern and western England and east Scotland, and very little in the rest of Scotland or most of Wales. This agrees very closely with the pattern of decline described earlier for the Kestrel and the Sparrowhawk most marked in eastern and southern England and to a lesser extent the Midlands, and spreading in the case of the Sparrowhawk to the west and north also. The Peregrine is absent as a breeding species from eastern England and the Midlands, but its decline is most marked in southern England, including the south-west, followed by those areas (Wales, north England and south Scotland) nearest to the areas of greatest pesticide use. The second correlation is with the timing of the decline. The use of the new synthetic pesticides increased steadily throughout the 950's, and the highly toxic mercury and chlorinated hydrocarbon seed-dressings were brought into use in the spring of 956, not widely at first, but reaching a peak in 959-6, after which the voluntary ban operated for some of them. The general decline of the Sparrowhawk appears to have begun about 955 and that of the Kestrel about

13 FIG. 2. The number of incidents reported of mortality due to toxic agricultural chemicals in each county in 96 (reproduced from Cramp, Conder and Ash 962, by permission of the R.S.P.B.) 36

14 TOXIC CHEMICALS AND BIRDS OF PREY The start of the Peregrine decline is less certain, but Ash noted it in Hampshire from 956 and Treleaven recorded it in his Cornish breeding population after 955 but before 958. Ash's observations in Hampshire also showed a drop in the numbers of Merlins from 954, of Hen Harriers from 956, and of Hobbies from 956 or earlier. The increasing infertility noted in the Peregrine in Great Britain and in the Bald Eagle and the Osprey in the U.S.A., since the growing use of chlorinated hydrocarbon pesticides, coupled with the fact that addled eggs of all three species have been found to contain pesticide residues, and the experimental proof that pesticides can reduce fertility in species such as Pheasants and Bob-white Quail, seems to establish a clear connection, and I am aware of no other possible explanation. Such a reduction in fertility may well be more effective in causing a population decline than the killing of adults, as witness the success of the campaign to eliminate the Screw-worm Fly {Cochliomyia americana) in Curacao and Florida (Carson 962). CONCLUSION After reviewing the evidence available, it is difficult to avoid the conclusion that the increased use of toxic chemicals, especially the persistent chlorinated hydrocarbons, has been the major factor in the recent decline of some of our diurnal birds of prey. If present trends continue, some species could be faced with extinction. The ban on the spring use of the three most toxic seed-dressings from January 962 should result in some improvement, and deaths of birds of all species were much reduced in the spring of 962. It should be noted, however, that less toxic chlorinated hydrocarbons, such as BHC, may still be used in seed-dressings, and the ban on aldrin, dieldrin and heptachlor does not extend to seed sown in the autumn in areas where attacks from the Wheat-bulb Fly are a danger, nor to their use in other pesticides, such as sprays. More important, perhaps, some of our birds of prey may have escaped the full brunt so far because their main breeding strongholds are in the north and west, where chlorinated hydrocarbons have so far been used on a much smaller scale. The danger exists, however, for BHC, DDT and dieldrin are used as sheep dips (Moore and Ratcliife 962) and Golden Eagles feeding on sheep carrion could be affected. And if the spraying of forests with chlorinated hydrocarbons, to combat either insect pests, as in the U.S.A., or voles, as in Germany, is begun on a large scale, this last refuge would be menaced. ACKNOWLEDGEMENTS My grateful thanks are due to Henry Mayer-Gross of the British Trust for Ornithology, R. S. R. Fitter of the Council for Nature, Roland C. 37

15 BRITISH BIRDS Clement of the National Audubon Society, Drs. N. W. Moore and D. A. Ratcliffe of the Nature Conservancy, and P. J. Conder of the Royal Society for the Protection of Birds, for allowing me to use unpublished material or for other help. SUMMARY (i) There is definite evidence of a sharp decline in the Peregrine in Great Britain in recent years, and strong indications of decreases also in the Kestrel and Sparrowhawk. Little information is available about the total populations of other diurnal species or of owls, but observations in southern England suggest that some of the former have also been affected. The Bald Eagle has decreased markedly in the U.S.A., and the Peregrine both there and elsewhere in Europe. (2) Pesticide residues have been found on analysis in the bodies of the Kestrel, Sparrowhawk, Buzzard, Barn Owl, Little Owl, Long-eared Owl and Tawny Owl in Great Britain, in the Golden and Bald Eagle in the U.S.A., in the Merlin, Whitetailed Eagle and Eagle Owl in Sweden, and in the Goshawk, Marsh Harrier and Montagu's Harrier in Holland. (3) A decline in fertility has been shown in the Peregrine in Great Britain, and in the Bald Eagle and Osprcy in the U.S.A., and eggs of all three species have been found to contain pesticide residues. (4) These facts, together with the timing and geographical distribution of the decreases, suggest that the increased use of toxic chemicals, especially the persistent chlorinated hydrocarbons, which both kill directly and have sub-lethal effects on fertility, is the major factor in the recent decline of some of our birds of prey. The position of these and the remaining species could be made worse if the use of such chemicals is extended in forests and other habitats in the north and west of Britain. REFERENCES ASH, J. S. (i960): 'Bird of prey numbers on a Hampshire game-preserve during '. Brit.Birds, 53: BERNARD, R. F. (962): 'Secondary DDT poisoning in a Sparrowhawk'. Auk, 79: CARSON, RACHEL (962): Silent Spring. Boston. CRAMP, S., and CONDER, P. J. (96): The Deaths of Birds and Mammals connected with Toxic Chemicals in the first half of i960. Report No. of the B.T.O.-R.S.P.B. Committee on Toxic Chemicals. and ASH, J. S. (962): Deaths of Birds and Mammals from Toxic Chemicals, January-June 96. The second report of the Joint Committee of the B.T.O. and R.S.P.B. on Toxic Chemicals, in collaboration with the Game Research Association. (963): Deaths of Birds and Mammals from Toxic Chemicals, September 96-August 962. The third report of the Joint Committee of the B.T.O. and R.S.P.B. on Toxic Chemicals, in collaboration with the Game Research Association. PLATE 22. Two specialists: the Short-toed Eagle {Circaetus gallicus), declining where cultivation is reducing snakes (page 46); and Griffon Vultures {Gypsfulvus) (also Egyptian Vulture, Black Kite and Raven) which have to face modern hygiene and the poisoning of carcases (pages 43-44) {photos: Eric Hoiking) 38

16 TOXIC CHEMICALS AND BIRDS OF PREY DEWITT, J. B. (955): 'Effects of chlorinated hydrocarbon insecticides on quail and! pheasants'. /. Agric. and Food Cbem., 3: (956): 'Chronic toxicity to quail and pheasants of some chlorinated insecticides'. /. Agric. and Food Chem., 4: and BUCKLEY, J. L. (962): Studies on Pesticide-Eagle Relationships. Interimreport to the National Audubon Society Convention, Corpus Christi, Texas. MORZER BRUIJNS, M. F. (962): 'De massasterfte van vogels in Nederland door vergiftiging met bestrijdingsmiddelen in het voorjaar van 960'. l^andbouwkundig Tijdscbrift, 74-4: MOORE, N. W. (957): 'The past and present status of the Buzzard in the British, Isles'. Brit. Birds, 50: (962): 'Toxic chemicals and birds: the ecological background to conservation problems'. Brit. Birds, 55: MORTON, R. K., and Vizoso, M. (in press): 'Dressed cereal seed as a hazard to- Woodpigeons'. Ann. Appl. Biol. MOORE, N. W., and RATCLIFFE, D. A. (962): 'Chlorinated hydrocarbon residues in the egg of a Peregrine Falcon from Perthshire'. Bird Study, 9: RUDD, R. L., and GENELLY, R. E. (956): 'Pesticides: their use and toxicity in relation, to -wildlife*. Calif. Dept. of Fish and Game, Game Bulletin, 7: TRELEAVEN, R. B. (96): 'Notes on the Peregrine in Cornwall'. Brit. Birds, 54: Appendix Scientific names of species mentioned in the text BIRDS OF PREY Golden Eagle (Aquila chrysaetos) Hobby (Falco subbuteo) Buzzard (Buteo buted) Peregrine (Falco peregrinus) Sparrowhawk {Accipiter nisus) Merlin {Falco columbarius) Goshawk (Accipiter gentilis) Kestrel (Falco tinnunculus) White-tailed Eagle (Haliaetus albicilld) American Sparrowhawk (Falco sparveriusy Bald Eagle {Haliaetus leucocephalus) Barn Owl (Ty/o alba) Marsh Harriet (Circus aeruginosus) Eagle Owl (Bubo bubo) Hen Harrier (Circus cyaneus) Little Owl (Athene noctua) Montagu's Harrier (Circus pygargus) Tawny Owl (Strix aluco) Osprey (Pandion haliaetus) Long-eared Owl (Asia otus) OTHER BIRDS Western Grebe (Aechmophorus occidentalis) Feral pigeon (Columba livid) Bob-white Quail (Colinus virginianus) Woodpigeon (Columba palumbus) Pheasant (Phasianus colchicus) House Sparrow (Passer domcsticus) PLATE 2 5. Two harriers: the adaptable Hen Harrier (Circus cyaneus), much persecuted but holding its own by nesting in many habitats from moorland to reed-beds (page 45); and the much more specialised Marsh Harrier (Circus aeruginosus), decreasing wherever marshes are drained (page 44) (photps: Eric Hosking) 39