Man and Birds. R. K. Murton

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, which occurred in only a quarter of the castings. The examination of castings probably underestimates the importance of rapidly digested invertebrates or vegetable foods, but it is clear that sheep (probably as carrion) are an important food source, although the raven, like the crow, is very much an omnivore and carrion feeder. There is no reason to doubt that the raven had similar food habits in the past, when it occurred throughout lowland Britain; in fact, we know that shepherds in Suffolk around 1850 were bitterly hostile to the bird – ‘five were among Mr Roper’s sheep at Thetford in August 1836’. Like the buzzard, the raven was a reasonably common breeder in Norfolk and Suffolk until about 1830, but it declined markedly thereafter, coincident with the rise of intensive keepering, and it had vanished by the end of the nineteenth century. While continued persecution was doubtless responsible for the final elimination of the bird, and was also probably responsible for making the carrion crow very rare in the second half of the nineteenth century, other factors doubtless contributed to the initial decline. Loss of carrion is usually given as the cause, and it seems likely that it was specifically the loss of sheep carrion that was responsible. In Norfolk and Suffolk this coincided with the period of active enclosure, particularly that of waste land and sheep walks from 1800 to the mid-nineteenth century. According to Arthur Young, half Norfolk yielded nothing but sheep feed until the close of the eighteenth century, when with enormous speed – enclosure was mostly achieved in twenty years – the land was covered with fine barley, rye and wheat. The rapidity with which enclosure was completed is manifested in west Norfolk