The Hen Harrier Read online

  Schipper (1975) found that passerine birds made up an important part of the Hen Harrier’s prey on the Flevopolders, Wadden Islands and Groote Peel (an inland area) in the Netherlands and in two areas of northern France. Young Pheasants and other nidifugous birds, rabbits and voles featured among the prey to varying degrees. In one breeding season in Flevoland, young pheasants were taken to such an extent that the percentage of passerines in the prey was considerably diminished, while in that season no small mammals were identified in the diet. Evidence of some differences in predation between the sexes was obtained; females caught more rabbits and pheasants, males more passerine birds. Although lizards and large insects were often taken by Montagu’s Harriers, very few lizards and large insects were found in the food of Hen Harriers in the study. Pellets from communal roosts in the Netherlands showed that when voles were abundant they formed the principal prey of wintering Hen Harriers, but when they were scarce, bird remains predominated in the pellets. Starlings formed almost 46% of all the passerine birds in pellets from the island of Terschelling. Schipper considered that wintering Hen Harriers showed a preference for voles but could switch readily to hunting passerine birds. He also cited a food study in Baye de l’Aiguillon, France, in which the proportion of voles and passerine birds in the prey varied from one winter to the next in relation to a fluctuating vole population. Nevertheless, he suggests that the absence of breeding Hen Harriers from large areas of Spain and Italy may be related to the lack of voles ‘or replacements’ in these regions.

  Geroudet said that voles were the main winter prey in France but, in summer, ground birds including nestlings and fledglings ‘qui volent mal’ were important food. Leverets and young rabbits were mentioned as occasional prey. Studies in Germany, Hungary, Yugoslavia and the USSR, summarised by Schipper (1975), all indicate the importance of voles and other small rodents in the diet. In Uttendorfer’s German study (1952) voles constituted 80% of the prey. Pellets collected from a winter roost, at which males predominated, in Belgian Lorraine, consisted mostly of the remains of voles. Some small birds had also been taken (Mois, 1975). Schipper, however, points out that Hen Harriers wintering in Italy, where very few small diurnal mammals are available, subsist almost entirely on passerine birds.

  The numerous old records of prey items in Britain and Ireland need to be treated with caution as the writers were generally more likely to record the killing of a game bird than any other prey. The rather frequent references to Hen Harriers killing Partridges in the 19th century reflect a period when Partridges were much more plentiful in the marginal upland ground than they are now. The game-books of Captain Clark Kennedy of Knockgray, in the Stewartry of Kirkcudbright, for the 1860s and 1870s, demonstrate this for many shoots in south-west Scotland. (Although hawks were quite often shot, too, none were specifically identified as Hen Harriers.) There were many old reports including some very angry ones, of Hen Harriers killing Red Grouse, notably in Ireland and the Scottish Highlands. St John claimed that prey included Black Grouse and Mallard but does not describe the circumstances and it is at least likely that such large prey was found injured or already dead. Many old regional accounts do, however, show a wide variety of small prey. In Devon the food was said to consist of mice, moles, lizards and small birds, but it is possible that there was some confusion between Hen and Montagu’s Harriers there.

  In his pioneer study of Hen Harriers in the 1780s, on Newton Common, Carlisle, Dr Heysham observed a male bring two Yellowhammers, a sparrow and a lark to feed its young. He also noted lizards as prey. St John’s verdict on the Hen Harrier’s food in Sutherland (1849) was: ‘though very destructive to game it compensates for this in some degree by occasional preying upon rats, vipers etc.’ The ‘etc’ perhaps covered all those smaller items of prey which were considered neither ‘useful’ nor ‘harmful’ in a sportsman’s balance sheet. Very few of the old ornithologists examined prey remains or stomach contents of Hen Harriers which had been killed, but F. M. Ogilvie (1920) made the following dissection notes in Suffolk and Norfolk:

  10 April 1900:

  an adult female contained the remains of a water vole.

  June 1904:

  an adult male was feeding on a small leveret.

  7 January 1907:

  female, immature; stomach contained the remains of a Chaffinch and a Skylark.

  30 March 1911:

  female, adult, feeding on Partridge; its stomach contained 4 ounces of flesh.

  Macgillivray (1836) found feathers of Ptarmigan in a female’s crop, possibly the only record of this species as prey of the Hen Harrier. In the Shetlands, Saxby (1874) said that Golden Plovers were the most usual prey—a rather surprising statement since harriers have apparently always been rare or absent in Shetland at the season when young, easily caught, plovers are available.

  There is rather more information on the prey of British Hen Harriers in some of their major haunts in recent years, although Nick Picozzi’s important findings, particularly regarding the effect of predation on Red Grouse in Lower Deeside, must be awaited. From Orkney, Balfour and Macdonald (1970) reported on prey brought to a nest and identified from a hide, rather late in the season, between 27 July and 14 August, when the chicks fledged. They recorded 23 mammals (5 rabbits, all caught by the female, and 18 Orkney voles), the same number of birds (1 Corncrake, 2 Lapwings, 1 Golden Plover, 2 Skylarks, 7 Meadow Pipits, 4 Starlings, 1 small wader and 5 small birds, unidentified) and 3 ‘small items’. Of 82 pellets from nests in the same year (1969), 79% were fur and 21% feather. Identifications from these pellets were:

  rabbit remains in

  3 pellets

  Orkney vole remains in

  28 pellets

  brown rat remains in

  1 pellet

  ‘Large Birds’ remains in

  10 pellets

  ‘Small Birds’ remains in

  15 pellets

  insect remains in

  12 pellets

  Twenty-three pellets without hard remains contained fur, and 5 contained feather. Meadow Pipit, Starling, Lapwing and Red Grouse were identified in pellets. In a lecture and in conversation with the writer, Eddie Balfour said that Orkney voles and young rabbits were the commonest prey, and many young Curlews and recently fledged Starlings were brought to nests. I am informed by Dick Orton that Starlings made up all the prey identified by a photographer at one nest in Orkney. It was thought that the lateness of the nest studied by Balfour and Macdonald might have accounted for the absence of young Curlews.

  Balfour believed that Orkney Hen Harriers have a food preference for voles. Chicks feeding off a young Curlew were seen to leave it for a vole brought in by the cock, but one such observation, though interesting, is clearly inconclusive. John Douglas considered that the spread of rabbits to the hills, after a succession of mild winters, was a factor in the increase of the Orkney harriers before 1933. He said that at that time the Hen Harrier’s habit of taking chickens from crofts was a threat to its survival, but there is no definite evidence of how commonly this has occurred in Orkney.

  The great success of the Hen Harrier in Orkney obviously owes much to the high numbers of the large Orkney vole (34–63 grams), apparently not subject to severe population crashes. Balfour and Cadbury suggest that the relative scarcity of breeding harriers on the island of Hoy may be due to the absence of voles. Fairly large numbers of harriers, though relatively few adult males, are seen in the islands throughout the winter, and Sunniva Green has told me that pellets from winter roosts suggest that voles are a main food source at this season. The harriers hunt the voles both in the lowland agricultural land and on the heathery hillsides; according to the Handbook of British Mammals (Southern, 1963), the voles occur ‘throughout pasture and arable land and up to at least 700 feet (210 m) on heather, thinning out thereafter’. In Orkney most of the hill ground is within the altitudinal limit of vole abundance. The relative absence of grazing by domestic animals, plus the moist climate, gives much lusher hi
ll vegetation than at comparable altitudes over most of mainland Scotland and northern England, where sheep have roamed for generations. The Orkney hill ground is thus an exceptionally good habitat for voles and, incidentally, provides the Hen Harrier with perfect nesting sites.

  As a visitor to the harriers’ Orkney breeding grounds I was impressed by the large number of hill breeding rabbits often feeding apparently unconcernedly on the patches of emerald grass and moss in the close vicinity of the harriers’ nests. Curlews are numerous breeding birds on and near the harrier nesting grounds; Balfour remarked that they were scarce early this century and have greatly increased. It is significant that Starlings nest in the heather and their newly fledged young are thus particularly vulnerable. In a few minutes’ flight, Orkney harriers can hunt a wide variety of habitats including moorland, pasture, arable and marsh. Red Grouse form only a minor part of harrier prey in the Orkneys. The future of Hen Harriers in Orkney may be considerably affected if the present trend towards reclamation of moorland for improved pasture and cultivation continues, though possibly more by a reducton of nesting areas than a shortage of prey.

  The food and hunting habitats of the Hen Harrier in the Outer Hebrides appear to have similarities with, and some differences from, Orkney. Robert Gray (1871) inferred that field mice (? voles) were the principal prey and Donald Guthrie, a keeper in South Uist from 1883–1905, wrote (1920): ‘The food is said to consist chiefly of mice, rats and voles, while sometimes they kill young rabbits, stripping the skin neatly back from the snout before eating them. Occasionally they kill grouse, but very rarely.’ Seton Gordon (1923) records that many young rabbits were taken in the sand dunes. In North Uist, in July 1974, I found a feathered young Golden Plover at a nest and in South Uist, as already described, saw a male harrier capture a Meadow Pipit on moorland. Dr J. W. Campbell told me that young waders formed a considerable part of the prey taken in these islands.

  With such fragmentary evidence on prey, I can do no more than comment on the most favoured hunting grounds. The Hen Harriers hunt partly over moorland but make regular flights to hunt the croftlands, machair and marshy fringes of lochs on the Atlantic side of the islands. These are undoubtedly where most prey is taken. Mr Snow, a keeper in South Uist, told me, in 1974, that even in summer he saw harriers most often over the machair, and after the young had fledged he had seen up to five together there. At this season young waders, larks and pipits are in great abundance on the machair and are probably the main attraction. Important differences from Orkney are the complete absence of young Curlews and the much heavier grazing of moorland by sheep; large tracts of hill ground look very bare and would be unlikely to carry a very high density of voles. In contrast, over parts of the moorland, and especially on islands in lochs, heather and willow scrub grow to heights of 120–150 cm, providing excellent nest-sites for harriers. Two such sites in South Uist were 5–6.5 kilometres from the nearest machair, which would be near the limit of hunting range for a cock feeding a hen or chicks. In one island, a nest has been found in rough ground with short heather, marginal to machair, suggesting that this site was used in preference to more suitable sites in deep heather at greater distances from the best feeding grounds.

  In mainland Orkney, at the present time, an area of suitable nesting ground holds about four times as many nests as there are likely to be in an area three times as great in the Outer Hebrides. It appears that Hen Harriers in the Outer Hebrides are at some disadvantage compared with Orkney, perhaps because substantial and easily caught prey, like the large Orkney Voles and young Curlews, are absent from the vicinity of nesting grounds; or perhaps because, in general, they need to make longer journeys to the best hunting grounds. The absence of breeding Hen Harriers from the Shetlands and the northern Outer Hebrides is particularly interesting and suggests that the lack of voles in these islands may be a serious disadvantage. Peter Hopkins points out that bird prey is likely to be much scarcer in the Long Island than in the Uists and Benbecula because machair and cultivation are largely confined to a small area in Harris. Bobby Tulloch has reminded me that there are no Kestrels breeding in Shetland, and Peter Hopkins says that the same is true in Lewis and Harris.

  In June 1975, I visited the nesting grounds in the Kintyre district of Argyll. In four to five year old conifer forest harriers were catching voles. The undulating hill landscape, hardly rising above 450 metres, is a little reminiscent of Orkney in spite of the extensive conifer forests on many lower slopes. Although grazed by sheep, the unplanted hill ground is lush with grasses, heather and rushes in this rain-washed peninsular, and in the southwest the lower, Atlantic-facing, cattle pastures are almost Hebridean in appearance. Before the forests were planted, Dugald Macintyre (1936) wrote that food at a nest in Kintyre was chiefly young wildfowl and ‘field mice’ (? voles). He said that the bulk of the winter food, identified from pellets at a roost, consisted of young rodents and Snipe. Peter Strang, a forest ranger, has been finding harrier nests in Kintyre for the past 23 years, and says that Meadow Pipits were the commonest prey, but many voles, Skylarks and young rabbits were taken, also a few young Red Grouse and occasionally young Pheasants.

  In the last few years there has been a marked decline in the number of harriers nesting in Kintyre. Although some former nesting grounds in forests are no longer tenable because of the height and density of the trees, it is difficult to believe that the shortage of nesting sites is enough to explain the decline. It is much more likely to be due to a reduction in easily caught prey, brought about by the loss of much open hunting ground and the increased difficulty of hunting within the wellgrown forests. In 1975, it was clear that the main concentration of breeding harriers was in the largest area of forest to be planted within the last five years, where voles were abundant and obviously an important prey of the harriers. In Arran, across the water from Kintyre, D. H. Macgillivray said in 1967 that a Hen Harrier at Corriecravie ‘used to take Lapwings’. I have already mentioned his observation of one capturing a Snipe.

  So, information on the Hen Harrier’s food in the three important areas of Orkney, the Outer Hebrides and Kintyre is uneven. The range of prey taken in Orkney is fairly well established, there are some interesting indications for Kintyre but far fewer for the Outer Hebrides. In all three localities, however, prey includes voles, young rabbits and small birds. Red Grouse numbers are low in Orkney and Kintyre and harrier predation on them cannot be significant in either. Nor is there a high population of Red Grouse in the harriers’ Hebridean haunts. I was informed by a game-keeper there that he was much more concerned with wildfowling than grouse shooting. Two contemporary keepers have no criticism of harriers as predators on game, while the same view seems to have been held by Guthrie while he was a keeper in South Uist from 1883–1905. Although information on the food of the Hen Harrier in the Outer Hebrides is much needed, I should be very surprised if it produced much evidence of predation on grouse.

  In 1967, David Stephen wrote of the feeding habits of Hen Harriers nesting in Scottish forest plantations. The locality was not disclosed but it was probably in west-central Scotland. He said that, in 1966, voles were scarce and wet weather made for bad hunting. ‘The harriers killed mainly birds but still not enough of them. In all nests there was famine and in all of them chicks were dying and being eaten. Only the intervention of the forester, supplying rabbits, saved the broods. This season (1967) was different. Six pairs hatched full clutches and reared full broods. Voles were up, so much so that a man could see one on foot at two minute intervals on a walk over the hunting grounds’. His general verdict was that Hen Harriers fed mainly on small mammals and birds, sometimes taking eggs or nestlings of ground-nesting birds. He saw a male bring a Woodcock chick to a brood. He also noted frogs and slowworms as prey. In Sutherland Bruin Nethersole-Thompson watched a Hen Harrier skin and eat a frog. David Stephen’s account is particularly interesting for its suggestion that in one Scottish forest, at least, fluctuating vole numbers had a decisive effect on har
rier breeding success.

  Young Woodcock

  On a Kincardineshire moor in the breeding season, Nick Picozzi has found Meadow Pipits, Red Grouse chicks and leverets the most common prey items. Mountain hares, rabbits and various birds were also eaten.

  My data on prey in south-west Scotland are given in Chapters 16 and 17 and Tables 17–23. They can be summarised as follows: in summer, young Red Grouse and passerine birds, especially Meadow Pipits and Skylarks, were the most common items. Most of the birds were young. Mammals, including voles, rabbits, hares and mountain hares, occurred in 30% of winter pellets examined from one roost but birds, mostly passerines, were found in 70%. Birds formed nearly 90% and mammals only 10% of remains in pellets from another roost in south-west Scotland (Dickson, 1970).

  There is much less evidence of Hen Harriers feeding on carrion in Scotland than in North America, but in November 1972 a female died after feeding on a carcase (? sheep) poisoned with mevinphos, near Dunblane, Perthshire (Bell, pers. comm.); and on 14 May 1974, Nick Picozzi saw a male at a very old carcase of a mountain hare at Kerloch, Kincardineshire, while Louis Urquhart has seen a female at an old rabbit carcase in Galloway (see here). Osborne (Harvie-Brown and Buckley, 1887) mentioned dead fish as food in Caithness and Jardine (1834) wrote that Hen Harriers repeatedly visited the Solway Stake nets to feed on dead fish. Saxby (1874) mentioned fish as food in Shetland, but did not know whether it had been found dead or alive. It seems likely that some of the larger items among winter prey in my south-west Scotland study were found as carrion.