The Hen Harrier Read online

  David Scott tells me that in Ireland the food varies somewhat from one place to another, but most of the prey in his experience consists of small birds. He once saw a female harrier with a partly-eaten rabbit which she was only just able to lift. He comments that grouse are almost rare birds in Ireland and he has only once found remains of a grouse at a nest. At one nest in the Slieve Bloom the main food appeared to be water birds, including Water Rails. No evidence of carrion feeding in Ireland was obtained by Scott.

  I have little information on the prey taken by Hen Harriers in England. In 1932, Desmond Nethersole-Thompson recorded that a pair nesting on a Surrey heath fed their young largely on young rabbits and also brought them a half-grown Lapwing, and a male Stonechat. A male on Lundy Island during a hard winter subsisted mostly on starving Fieldfares (D’Urban and Matthew, 1895). Dr Ken Brewster, however, was informed ‘by a reliable ornithologist’ that Hen Harriers only appeared in one part of southern England when voles were abundant. Graham Williams tells me that he once found the remains of a young Red Grouse and a young Pheasant at a nest with six large young, in Wales. As I have pointed out in my account of prey in south-west Scotland the remains of larger kills, which cannot be entirely eaten, are likely to be found in or near nests with large young, whereas small prey items, which may be more numerous, are usually only traceable from pellets.

  A minor part of Hen Harrier food, in both America and Europe, consists of insects, particularly beetles. These may be of some importance to young birds in their first weeks of hunting. In America, Breckenridge (1935) found that the young ate some fruit, and he recorded blueberry, raspberry and dogberry.

  I have listed in Table 2 specifically identified prey from British and Irish sources but I do not claim that it is exhaustive.

  Prey selection

  The foregoing account has shown that small mammals, particularly voles, are the main food of Hen Harriers in many parts of their range. In the Norwegian fjelds, and probably in some afforested areas in Scotland, a shortage of voles may greatly reduce breeding success, or even inhibit breeding, even though bird prey appears plentiful. The dense population of harriers in Orkney is much dependent on the large Orkney vole, the numbers of which seem never to drop to very low levels. This rich food source is augmented by the plentiful supply of rabbits and, in summer at least, there is also a good supply of the young of passerine and wading birds.

  Schipper suggests that the absence of voles or ‘replacements’ may explain the absence of breeding Hen Harriers from large parts of Spain and Italy. Yet it is clear that thriving populations of Hen Harriers in parts of Scotland, in Ireland (where voles are absent), and in Holland can subsist principally on bird prey. In such instances passerines often form a high proportion of the birds taken but larger birds such as well-grown young Red Grouse, Pheasants and Curlews are sometimes important, too. If voles or other small mammals are scarce, or absent, the requirement is an abundant population of birds living in habitats suited to the harriers’ hunting methods. Since the average weight of prey taken by female Hen Harriers, in Schipper’s Dutch study, much exceeded that of males (122 grams to 68.9 grams), it may be that a good supply of larger prey, such as game birds or rabbits, is important to females; and where voles are scarce, might even be essential for the most successful breeding. Schipper’s very interesting evidence, that males took the higher proportion of agile passerine birds, further suggests a different emphasis in the prey selection of the sexes. The fact that females usually hunt nearer to their nests than males might explain why, in south-west Scotland, most nests are close to areas of moorland or young forest plantations, where young Red Grouse can be easily found. Analysis of sightings of harriers hunting in winter in the same part of Scotland (see Chapter 17), shows that males made up a higher percentage of those seen hunting lowland pasture and arable land than moorland, conifer forest or marsh. At this season, passerine birds were most numerous in the lowland fields.

  In their discussion of predation by Marsh Hawks, Errington and Breckenridge suggested that they preyed mainly on a vulnerable ‘over population’ of prey species. This vulnerable element was said to be living beyond the capacity of the habitat to accommodate it adequately. An obvious example of this occurs when voles, fledgling birds, or nests are suddenly deprived of protective cover by operations such as grass cutting or harvesting. But Errington and Breckenridge had especially in mind the normal, large surplus of birds or mammals which dies from starvation, or other causes, having failed to find adequate living conditions. In their research on Red Grouse in Scotland, Jenkins, Watson and Miller (1964) convincingly showed that grouse killed in winter by predators such as Hen Harriers were nearly always surplus birds which had failed to establish themselves as territory holders. Starvation was usually their fate if they were not killed by a predator. So, grouse losses to harriers in winter had little or no effect on the breeding stock in the following season.

  In the breeding season most bird prey is young and is therefore taken from the most vulnerable parts of the prey populations. It is obvious that, whatever the prey species, a high proportion of the young will not survive long enough to breed. The birds and mammals commonly killed by Hen Harriers all belong to very successful, numerous species and it would be surprising if harriers ever had any controlling effect on prey such as Meadow Pipits, Skylarks, or the huge winter finch flocks which they hunt. Nevertheless, the Craigheads did show that, in their study area, the total effect of all the predators, which included some Marsh Hawks, limited a population of meadow mice in early spring, when the mice were especially vulnerable in minimal vegetation. In Britain, Lockie (1955) considered that Short-eared Owls could hasten the decline of field voles between April and June but probably had little effect on their numbers later. It is not known whether Hen Harriers, in Britain, ever have a depressive effect on vole numbers.

  It is obviously true that the creation of grouse moors offers the Hen Harrier a suitable hunting habitat, with large numbers of possible prey. Yet, even if it were proved that several breeding pairs could limit the number of young grouse available to the guns, this would appear not to be important since, according to the findings of Jenkins, Watson and Miller, not all the potential crop was shot on the moor studied by them, and a surplus of birds, most of which died before the next breeding season, always remained after shooting. In the eyes of a keen grouse shooter it is a crime to disturb a grouse shoot and no one will deny that a harrier can cause grouse to fly and scatter, but the same applies to many large, broad-winged birds, not necessarily predators. Unfortunately, the Hen Harrier is still much hated on most grouse moors, and where large sums are paid to shoot grouse, it appears that legal protection of harriers avails little or nothing. I return to this subject in my final chapter.

  Food consumption

  The Craigheads found that a captive female Marsh Hawk in the autumn and winter months ate an average of 100 grams of food daily; and a male in spring and summer ate an average of 42 grams daily. Raptors in the weight range of Marsh Hawks and Hen Harriers required an average of 12.5% of their body weight in spring and summer, and 15.8% in autumn and winter. The average weights of male and female Hen Harriers are given by Brown and Amadon as 357 grams and 483 grams respectively, but they were considerably lighter ‘on migration in China’. Marsh Hawks were noticeably heavier, averaging 472 grams for males and 570 grams for females. The approximate weights of some prey species in Britain are: Meadow Pipit (adult) 20 grams (J. Watson); field vole (adult) 25–40 grams, Orkney vole (adult) 50 grams (Handbook of British Mammals); Red Grouse (adult) 629 grams (D. A. Ratcliffe). Young of any of these are of course in a lower range of weights.

  I do not know what proportion of prey weights can be counted as ‘food’ but some speculations on the amounts of prey a Hen Harrier needs to kill for itself can be made. A female in winter, having the maximum requirement for a Hen Harrier, might need to kill up to four Meadow Pipits or two Orkney voles, while a single Red Grouse could be sufficient for tw
o–three days. It would seem that if Hen Harriers could readily kill full-grown Red Grouse, life would be easy for them. It is probable that only females are commonly able to kill adult Red Grouse and even they are most likely to capture those which are already weakened from food shortage, disease or injury. On the other hand, the hunting capabilities of males presumably make it easier for them to live off a larger number of small items, than off a small number of large ones.

  * In summer, 1976, R. C. Dickson (pers. comm.) saw an immature male kill an adult cock Red Grouse.

  CHAPTER FIVE

  The Breeding Cycle: Courtship to Incubation

  Nesting habitats

  My account of Hen Harriers breeding in a particular region (south-west Scotland) is given in Chapter 9 et seq. The present chapter traces the general pattern of behaviour throughout the breeding season and refers to a number of specialist studies, particularly those of Balfour in Orkney, and Hamerstrom in Wisconsin, USA.

  The breeding habitats of the Hen Harrier include most of those which I have summarised as hunting habitats in the previous chapter. A few of the hunting habitats, such as bare grassland and saltings, are unsuitable for breeding owing to lack of cover for the nest, which is always built on or very near the ground. Provided adequate hunting grounds are available in the vicinity and the site is undisturbed, Hen Harriers can nest successfully in a variety of moorland or marshland vegetation, in the dense cover of young conifer forests, in scrub of birch or willow, and even in fields among crops such as wheat or kale. Nevertheless, in Britain and Ireland during the present century, the breeding grounds have been almost exclusively on moorland or in young conifer forest.

  The contrast between the landscape and atmosphere of the harrier nesting country in Orkney or the Outer Hebrides, and that of the great tracts of conifer forest of south-west Scotland, is extreme. In Orkney, the background is the seemingly limitless sea from which the spume often flies from a multitude of white crests all the way across the Pentland Firth. Between rain showers, the towering headland of Hoy is caught in pearly sunlight, and the jigsaw of brightly patterned cultivation with its clear-cut farmsteads contrasts sharply with the spongy moorland above the waists of the hills. These, the harrier nesting grounds, have been evocatively described by Desmond Nethersole-Thompson: ‘squat hills, brown, barren and storm-swept, rise gradually from those countless lochs and lochans which twinkle in the sunlight like blue eyes in the deep brown faces of the valleys’.

  In North and South Uist, the nesting grounds lie in that mysterious heartland of moor and bog, so deviously intersected by lochs and arms of the sea that the whole forms an unbelievably intricate mosaic, from which protrude hills of glistening, almost naked rock. To my mind these islands, where the Hen Harrier is inclined to be elusive, are the most delectable of all the nesting grounds which I have visited. Often all is obliterated in smearing rain, but when the clouds lift, the colours of the islands and the sea beyond have an almost magical freshness.

  I shall describe the nesting grounds on the moors and in the forests of a mainland area of Scotland in Chapter 14. I confess that the serrated outlines of afforested hills seem to me to provide a less becoming setting for harrier watching than the open moorland, with its infinite variety of colour and texture, changing almost imperceptibly through the seasons. Yet the forests hold a certain charm, not least in early spring when the blue-green richness of sitka spruce seems to belie the time of year. In Kintyre, although the nesting places are mostly in the forests, the surroundings have a charming variety, with hints of both Orkney and the Outer Isles.

  Every ornithologist knows the thrill of discovering familiar birds in strange lands. So it was with special pleasure that I met the Hen Harrier, evidently breeding, in the conifer plantations of the Auvergne, some 600 metres up, in the heart of the Massif Central—a countryside remarkably reminiscent of harrier haunts in the Galloway forests. Further north in France, Hen Harriers were almost certainly nesting neighbours to Marsh and Montagu’s, in the parched heathland near a cluster of lakes in the district of La Brenne. Bannerman said that in Scandinavia the Hen Harrier has two distinct breeding grounds: ‘one in the lowlands of central Sweden with their great reed and sedge-fringed lakes, the other on the high plateaux’.

  As I have shown in the historical section of this book, fens and marshes were formerly regular nesting haunts in Britain and it seems possible that, where sufficient habitat of this kind still exists, they might become so again, especially since an increasing colony now flourishes not far away in Holland. Two birds ringed as young on the moors of Orkney have been found during the breeding season in Holland and may well have been breeding there. The habit of nesting in standing crops has long been known in Continental Europe, but in 1964 Terrasse said that, in France, modern agricultural methods did not give harriers enough time to rear young in cultivated fields. Geroudet knew of nesting in France in corn and kale fields, among whins and heather on heaths, in a little copse among dense reeds and in sedges bordering a marsh. Although there is no proof that Hen Harriers ever nested in cornfields in Britain (as Montagu’s have done) it certainly seems possible that ‘modernised’ agriculture, in the form of the so-called ‘prairie’ farming of eastern England, might provide a possible nesting habitat. It is probably true, however, that Hen Harriers are generally attracted by the habitat of their birth unless, perhaps, the presence of already established birds (as in Holland) acts as an introduction to different nesting terrain.

  My own belief is that nesting in conifer plantations, in Scotland, was begun by birds moving a short distance from adjacent moorland, probably because of persecution, and since in the early years of afforestation the habitat change is gradual this was not as great a change as it might appear. The recent remarkable increase of the Dutch breeding population of Hen Harriers has taken place largely in low-lying coastal habitats, mainly sand dunes in the Wadden Islands and reed-beds in the polders; according to Schipper vegetation in the dunes is principally marram grass Ammophila arenaria, sea buckthorn Hippophae rhamnoides, bog rush Schoenus nigricans and creeping willow Salix repens. So far as I am aware there is only one certain contemporary instance of Hen Harriers breeding in sand dunes in Britain (anon). If there is indeed an interchange between British and Dutch breeding stock perhaps dunes and reed-beds may become established breeding haunts in Britain.

  Although Short-eared Owls almost invariably colonise young conifer plantations which contain an abundance of voles, the requirements of breeding Hen Harriers are evidently more complex. Those who knew the colony which flourished for some years in Kielder Forest, Northumberland, are still puzzled by its recent disappearance, as they consider that there is no obvious lack of young plantations or moorland similar to those which used to provide food for the colony. In Wales, Graham Williams reports that the nesting habitat is largely moorland and there has been hardly any colonisation of the extensive young forests; and in southern Scotland vast areas of such habitat, where Short-eared Owls and Kestrels abound in good vole years, have gained only small numbers of nesting Hen Harriers.

  When I was shown some of the Welsh harrier ground, in 1975, I was immediately captivated by the spaciousness of these rather high heather-clad moors. Nest sites there are commonly at between 375 and 600 metres, but most nesting in Britain occurs at elevations between 150 and 450 metres. David Scott and others inform me that the same applies to Ireland, where the nesting environment is commonly a mixture of moorland and young conifer plantations. David Scott tells me that moorland in the vicinity of the plantations is undoubtedly the most usual nesting situation, but there is some local variation. King, for instance, has found that most nests in Kerry are well clear of forest; and Scott attributes the siting of a number of nests in the Wicklow forests to inadequate cover on neighbouring moorland. Jones, who describes four nests in open moorland and two in young forest, suggests that the association of Hen Harriers and trees in part of Munster may be fortuitous, since forests are now so widespread there that
any nesting site is bound to be fairly near a plantation, and Scott agrees that the same applies to Wicklow. It may well be that the lack of nesting in some districts, either in forest or moorland, is due to food shortage at higher elevations, particularly during the period when males do all the hunting and need to find an abundance of small prey.

  In North America, Bent (1937) gave many examples of the Marsh Hawk nesting in swamps, often much overgrown with bushes, but he also mentioned nesting in dry habitats such as open grassland and wheatfields. Hamerstrom’s study area of 6,500 hectares, in Wisconsin, which held up to 25 nests in one season, included both dry grassland and low-lying swales of willow and sedge, but over 60% of the Marsh Hawks’ nests were in the latter.

  Return to breeding grounds; pairing and courtship

  Anyone who has watched an area where Hen Harriers have bred over a number of years is bound to be struck by their faithfulness to established territories and their apparent reluctance to colonise other areas which appear equally or more suitable, not far away. Although Hamerstrom (1969) found in North America that conifer plantations were deserted as nesting grounds when the trees were 4–6 years old, my experience in Scotland (see Chapter 12), has been that in some instances nesting continues until the trees are at least 14–15 years old. In a few instances, I have been reasonably certain that an individual bred in the same territory in successive years. Balfour wrote that many harriers in Orkney did so, and one female bred in the same area for six years, but he also knew of cases in which known birds moved around from year to year, and in one case a hen nested in ‘five different stations’ in six consecutive seasons. Hamerstrom, working with colour marked birds in Wisconsin, found that pair fidelity from year to year was extremely rare. In both the Orkney and Wisconsin colonies there was a strong suggestion, from the low percentages of marked birds which returned, that the colonies were replenished by immigration. As I have said in Chapter 7, a few recoveries of Orkney-ringed young indicate that, later, these sometimes breed or attempt to do so in widely scattered parts of the northern and central Highlands of Scotland. There are, therefore, strong hints that Hen Harriers often settle to breed in areas distant from their birth place. My own observations, at a winter roost in south-west Scotland, lead me to believe that this may be facilitated by individuals from different breeding areas mingling and even pairing there.