Collins New Naturalist Library. R. Murton K.

the second much more drastic and this time national decline took place, associated with a fall in nesting success and the frequent breaking and disappearance of eggs which the birds appeared to be eating themselves (see here). While the evidence that toxic chemicals were responsible was necessarily circumstantial, it was such that no reasonable person could wait for cut and dried scientific proof while there was a grave risk of losing much of our wild life in the meantime, and a voluntary ban on the use of these chemicals was agreed. All the same, the recovery of dead peregrines and their infertile eggs containing high residues of organo-chlorine insecticides, together with the coinciding of the decline with the increased usage of the more toxic insecticides, seems to indicate that pollution from these chemicals does account for the loss of these birds. In fact, fifteen infertile eggs from thirteen different eyries in 1963 and 1964 all contained either D.D.T., B.H.C., dieldrin, heptachlor or their metabolites. The distribution and residue level of these insecticides in adults and eggs shows that birds at the top of the food chain are highly susceptible to contamination. A sample of 137 of those territories examined in 1962 was again checked in 1963 and 1964. In 1962, 83 of these were occupied and in 42% of these young were produced (this is the best measure of nesting success), in 1963 only 62 of these territories were occupied but 44% produced young while 66 were occupied in 1964 and 53% produced young. There thus seems some hope that the alarming decline in numbers has been halted and that breeding success is returning to a more normal level. To complicate the picture, though certainly unconnected with the effect of toxic chemicals, there is some evidence that there has been a gradual fall in the peregrine population of the Western Highlands and Hebrides since the start of the century. Whether or not this decline followed the depletion of vertebrate prey in the region already referred to, is not at all clear.

      Peregrines capture live prey, usually in flight, and, as Table 3 shows, domestic pigeons form a large proportion of the food in the breeding season. The peregrine is called duck hawk in the United States, and it can sometimes be seen on the estuary in winter instilling panic into wigeon and teal flocks, although duck form a relatively unimportant prey in the summer. It is surprising that the wood-pigeon is not taken more frequently, but it is likely that the adults, which average 500 gms, are too big; domestic and racing forms of the rock dove weigh 350–440 gms. In fact, the only wood-pigeons I have seen killed by the peregrine, and this was in S. E. Kent, were juveniles about 2–3 months out of the nest. In this area of Kent, peregrines seemed to do much better in autumn by concentrating on the flocks of migrants, particularly starlings, which pour into the country over the cliffs at Dover. It is not known to what extent peregrines take domestic or racing pigeons which have become lost and have joined wild populations and as a result are of no value to their owners. Ignoring this factor, but making various allowances for breeding and non-breeding birds, Ratcliffe estimated that the pre-war peregrine population (650 pairs) would consume about 68,000 pigeons per annum, while the depleted population in 1962 would eat about 16,500. This latter figure represents about 0.3% per annum of the total racing pigeon population of Britain, numbering about five million birds. To put this in proportion, there are about 5–10 million wood-pigeons in Britain, depending on the season, which are widely regarded as a pest of mankind – yet mankind happily finds food for 5,000,000 domesticated pigeons. In Belgium, the home of racing pigeons (one-third of the world’s pigeon fanciers are Belgian and one-fifth are British), the Federation of Pigeon Fanciers was offering a reward of 40 francs for evidence of the killing of red kite, sparrowhawk, peregrine or goshawk, in spite of the fact that Belgium has ratified the International Convention for the Protection of Birds under which such subsidies are forbidden. While education is again the answer to this kind of attitude it is slow to take effect. A big problem arises because pigeon racing, like greyhound racing, provides a relaxation which can be coupled with betting. As some pigeons are fairly valuable, and the loss of a race through a bird failing to home results in lost prizes or betting money, it is all too easy to lay the blame on a bird of prey.

      There is much evidence that predators select ailing prey, and when this additional allowance is made it seems ludicrous to claim that peregrines can really do significant harm to racing pigeon interests. Rudebeck observed 260 hunts by peregrines. Of these only 19 were successful and in three of the cases the victim was suffering from an obvious abnormality. For 52 successful hunts by four species of predatory bird (sparrowhawk, goshawk, peregrine and sea eagle) he recorded that obviously abnormal individuals were selected in 19% of the cases – a much higher ratio of abnormal birds than would normally be expected in the wild. Thus when Hickey (1943) examined 10,000 starlings collected at random he reckoned that only 5% showed recognisable defects. M. H. Woodward, one time secretary of the British Falconers’ Club, quotes the case of 100 crows killed in Germany by trained falcons belonging to Herr Eutermoser. Sixty of these crows were judged to be fit, but the remainder were suffering from some sort of handicap, such as shot wounds, feather damage or poor body condition. But of 100 crows shot in the same district over the same period, only 23 were judged abnormal on the same criteria.

      FIG. 13. Seasonal changes in the number of wood-pigeons (top figure) or domestic pigeons (lower figure) in the diet of the goshawk in Germany. The dotted line is based on Murton, Westwood & Isaacson 1964 and represents seasonal changes in the population size of the wood-pigeon. Goshawks take more pigeons when the population size of their prey is swollen by a post-breeding surplus of juveniles, domestic pigeons having their peak breeding season earlier than wood-pigeons. (Based on data in Brüll 1964).

      Table 3 summarises the diet of two other birds of prey, the sparrowhawk and goshawk. Apart from demonstrating how two closely related species differ in their food requirements, enabling them to co-exist in the same deciduous woodland habitat without competition, the table shows the importance of the wood-pigeon in the diet of the goshawk. The fact that the goshawk is slightly larger than the peregrine and is also a woodland species accounts for its ability to take those larger pigeons which the peregrine rarely utilises. Many people have suggested that the goshawk should be encouraged to settle in Britain to help control the wood-pigeon population, but there is no evidence that it would take a sufficient toll to be effective, for the same reasons that eagles and harriers do not control grouse numbers. Fig. 13 supports this view by showing the proportion of wood-pigeons in the prey of goshawks at different seasons, against seasonal changes in wood-pigeon numbers. Clearly wood-pigeons are mostly eaten at the end of the breeding season when many juveniles are available, and in mid-winter when population size is still high. In spring, when the goshawk could potentially depress population size below normal – and hence really control numbers – it turns to other more easily captured prey. In contrast, feral and domestic pigeons breed earlier in the year and have a population peak in June; this is when they are most often caught by goshawks.

      Neolithic husbandmen were doubtless familiar with the presence of ravens and crows near their domestic animals, long before biblical shepherds were tending their flocks aware that these birds were a potential menace to a young or weakly animal – the eye that mocketh at his father … the ravens of the valley shall pick it out (Proverbs 30: 17). Predacious habits and black plumage, burnt by the fires of hell, long ago made the crows prophets of disaster. A suspicion of such augury still persists among those who today think it appropriate to hang corvids and birds of prey on some barbed wire fence or makeshift gibbet; while these crucifixions may well release human frustrations, they do nothing whatever to deter the survivors (see Chapter 12).

      Ravens are no longer widely distributed throughout Britain as they were in medieval and even more recent times, but there are still frequent complaints from hill farmers and shepherds in parts of Wales, northern England and Scotland that ravens, and hooded or carrion crows, sometimes kill or maim lambs and even weakly ewes. According to Bolam (1913) sheep, mostly in the form of carrion, comprise the major part of the diet of ravens in Merionethshire, sheep remains being found at least three times more frequently in castings than remains of any other food item (these including rabbits, rats, voles and mice, moles, birds, seashore and other invertebrates, snails and large beetles and some vegetable remains of cereals and tree fruits). Similarly, E. Blezard (quoted by D. Ratcliffe 1962) found sheep remains in over half the castings he examined from birds in northern England and southern Scotland, the next most important item being rabbit,