The Hen Harrier Read online

  The opening chapters of this book discuss and compare all the different species of harriers. Next, in Part One I have dealt in some detail with the Hen Harrier’s history and present status in Britain and Ireland, and continued with chapters on its hunting behaviour, food, breeding habits, migration and winter distribution. Part One concludes with the short chapter on the Hen Harrier as an artist sees it. Part Two consists of an account of my own field studies in south-west Scotland and includes data on breeding and food. The penultimate chapter of Part Two describes a long study of communal roosting in this region.

  While the greater part of my own fieldwork on the Hen Harrier has been done in south-west Scotland (Galloway) I have watched Hen Harriers in many other important haunts and discussed the species with numerous ornithologists. It has been particularly interesting to find regional differences of breeding habitat and food. I have also researched into the most important European and American studies and have referred to relevant work in the other parts of the world.

  Note: The tables referred to throughout the text are to be found, for convenience of reference, at the end of the book.

  Marsh Harrier

  CHAPTER ONE

  Harriers of the World

  General and specific characteristics

  The harriers (genus Circus) are all fairly large hawks with long, broad wings, long tails and legs and slim bodies. Different authorities recognise either nine or ten species (see Origins and structural adaptations) and one or more species is found in every continent and on many islands. Their rather low wing-loading (the ratio of body weight to wing surface area), facilitates buoyant, sustained flight and even enables them to make considerable sea crossings in steady flapping flight. In such crossings they are less dependent than many raptors on assistance from rising air currents. Nick Picozzi, however, has seen a harrier, probably Montagu’s, use thermals in company with other raptors when crossing the Bosphorus, but he noted that Hen Harriers used a high travelling flight on migration through the Pyrenees. Jeffrey Watson has observed Montagu’s and Marsh Harriers on spring migration, crossing the Sahara in direct flapping flight at about 15 metres above the ground.

  Harriers are capable of very high soaring flight in the manner of buzzards and eagles and most of them regularly soar at heights of a hundred metres or more when displaying in spring, and at such times perform spectacular aerobatics. All harriers have a remarkably similar outline in flight. When hunting the wings are flapped in an apparently leisurely manner, much interspersed by glides on stiff, slightly raised wings held in a very shallow ‘V’. A non-ornithlogist once commented aptly on the ‘hunch-shouldered’ silhouette of a gliding Hen Harrier. Most harriers habitually hunt close to the ground, though some, like the Marsh Harrier, which frequently hunts over tall vegetation, tend to cruise higher than others. Prey is generally caught by a pounce or grab in which the long legs are used to maximum effect. While some species, including the Hen and Cinereous Harriers and the African Marsh Harrier, can take flying prey, the majority of harriers capture most of their prey on the ground.

  All harriers are birds of relatively open country. Their long wings and comparatively laborious searching flight do not equip them for successful hunting in closed woodland. In Europe the Marsh Harrier is the most typical species of marshland but in its absence in North America the Hen Harrier (or Marsh Hawk) occupies this habitat as well as drier ground. Aversion to large tracts of high forest is well demonstrated by the distribution of the South American Long-winged Harrier. It occurs in Trinidad and Surinam, north of the equator, is entirely absent from a vast area of mainly tropical forest in Brazil, but is common further south in the pampas of Paraguay and Argentina. Apart from the Marsh Harriers, it is the only species of harrier which breeds both north* and south of the equator.

  Most harrier species are wholly or partially migratory, exceptions being some of the island races of the Marsh Harrier and possibly the two entirely African species, the Black Harrier and the African Marsh Harrier. Some, like the Spotted Harrier of Australia, make restricted movements within a continent, while at the other extreme, the Pallid Harrier is a long distance traveller between breeding grounds in Central and Northern Europe and Asia and wintering grounds as far south as Sri Lanka in Asia and Cape Province in Africa. Some Pied, Montagu’s and Marsh Harriers must also cross the equator on their migrations.

  It is not surprising that a bird which generally shuns woodland almost invariably nests and roosts on the ground, in spite of the many risks which this entails. The only exception, at least in nesting, is the Spotted Harrier of Australia, which is, in many ways, the least typical member of the genus. It builds a large nest in a tree, sometimes in a tree-top, and is most often seen perching in trees though its hunting habits and food are very similar to those of other harriers.

  The communal roosting of Hen Harriers in their winter quarters is described later in this book, but the habit is common to at least six of the ten species—Hen, Marsh, Pallid, Montagu’s, Pied and Long-winged Harriers. Dresser (1878), recorded an observation of thousands of Montagu’s Harriers collecting to roost in the Department of Vienne, France—sadly, such numbers of this species can only be dreamed of today. There are several accounts of smaller roosts of Montagu’s Harriers, both in Europe and Africa. A spectacular roost of 160 Montagu’s and Marsh Harriers in Kenya was described by Meinertzhagen (1956), and Delacour (1966) has told how, in the 1920s, he watched many Pied and Oriental Marsh Harriers settling noiselessly to roost in a marshy depression among the sand dunes near the western seaboard of Annam (Vietnam). In New Zealand, Gurr (1947) found a swamp roost of more than 100 Australasian Marsh Harriers. Communal roosts of Pallid Harriers are described by Ali and Ripley (1968) and others, both in India and Africa, while in Surinam Reussen (1973) observed up to 32 Long-winged Harriers gathering to roost in a flooded rice-field. Several writers have commented that the birds must collect from a vast area to join these roosts. While the habit is most common in winter quarters, Pallid Harriers have been found (Ali, 1968) to roost communally in ploughed fields or other bare ground during migration and Weis (1920) recorded roosts of Montagu’s Harriers after the breeding season. He noted that adult males used a different part of the roosting ground from adult females and juveniles.

  Fig. 1 Breeding ranges (for scientific names see Table 1)

  Most, and probably all, harriers have a similar pattern of behaviour in the breeding season, with the female incubating while the male brings the food, but the Spotted and Black Harriers are not sufficiently known for a positive statement to be made on this subject. The transfer of prey in flight in the food pass from male to female, in the nesting area, probably occurs in all the species. One remarkable feature of the Spotted Harrier, mentioned by Brown and Amadon, is the great length of the incubation and fledging period, which together are said to be 95–100 days, but they comment that this needs checking.

  Some of the island races of the Marsh Harrier, like the Reunion Harrier, which might be classed as distinct species, are among the rarest birds in the world, but the rarest acknowledged species is the Black Harrier of Southern Africa. According to Peter Steyn this beautiful bird is found mainly in dry country. It hunts the Karroo regions of Cape Province, quite often over snow-covered slopes of the foothills. Steyn writes that virtually nothing is known of its breeding habits, but he believes that some nests are in wheat fields and one was found in fairly tall dry grassland.

  While the categories of prey taken by the various harriers show considerable overlap—small mammals and birds being very generally taken—Schipper (1973) has shown that differences in size and structure affect their hunting agility and killing efficiency and reduce the overlap of species living in the same district beyond what might be expected from their superficially similar hunting behaviour. For instance Marsh Harriers, with the largest and most powerful feet, exploited heavier, less active prey while the smaller footed Hen Harriers were particularly agile at catching full grown passerine birds
, but Montagu’s Harriers, with the weakest feet, relied particularly on young passerines, lizards and insects. Sexual dimorphism, in size and structure, permits diversification of prey within a single species. The breeding seasons of the three species, in Holland, began at different times and this was a factor facilitating co-existence. Harriers which showed the greatest differences in average weights of prey were most often hunting at the same period. Nieboer (1973) considered that Montagu’s Harrier was a more agile hunter than the Hen Harrier, as might be expected from its slimmer build and more buoyant flight, but Schipper suggests that the relatively shorter, ‘more fingered’ wings of the Hen Harrier (more like those of Accipiter hawks) provide greater manoeuvrability in capturing flying prey.

  Some harriers, certainly, occasionally kill young poultry but there is little evidence that this is ever a major prey item. There are a few records of birds’ eggs as harrier food. Carrion, either road casualties or kills of other predators, is probably more important to some harrier species than commonly recognised. Ronald Lockley tells me that the Australasian Marsh Harrier is very often seen on roads in New Zealand, feeding on birds or rabbits which have been killed by traffic. Brown and Amadon mention both Marsh Harriers in Africa feeding on the kills of larger predators, while the North American Hen Harrier depends to a large extent on roadside carrion in severe winter weather. Food studies (see Chapter 4) have shown that a single species of harrier may concentrate on quite different prey at different seasons, even in the same locality. Montagu’s Harriers, for instance, feed largely on birds and voles in the early part of their breeding season, but as summer advances lizards and large insects become important in their diet where they are available in Europe, and probably form the bulk of prey in African winter quarters. Neufeldt (1967) found that rodents made up 85% of the food of the Pied Harrier on its breeding grounds in Amurland, USSR, but in Burma, frogs and large insects are the main prey. Even the more powerful species such as the Marsh Harrier, whose food has been studied in detail by Schipper and others, take mainly young or injured specimens of their larger prey items such as pheasants, waterfowl and rabbits. Schipper has proved that the same individual Hen, Marsh or Montagu’s Harrier takes prey of differing composition in different seasons, switching from voles to birds when the former are at a low density. There are many records of harriers feeding on fish but I have only found one observation of fish being caught alive, Ali and Ripley (1968) citing Willoughby P. Lowe’s account of migrating harriers, probably Pallid Harriers, pursuing and catching flying fish as they skimmed over the waters of the Red Sea.

  Fig. 2 Breeding ranges of Hen, Montagu’s Pallid and Pied Harriers

  Females in harrier species are generally longer-winged and heavier than males. Schipper’s studies of prey taken by Marsh and Hen Harriers show that in both species the average weight of prey taken by females was heavier than by males but Nieboer attributes this to the greater foot-size of the females. In the Montagu’s Harrier the sexes are of nearly similar size and in the Pallid and Pied Harriers the size differences between the sexes are less than in most other members of the genus. No significant difference in average weight of prey taken by male and female Montagu’s Harriers was established by Schipper. Nevertheless, male Montagu’s Harriers, like male Hen Harriers, did capture more fledged or full-grown passerine birds, than did females. The possible hunting significance of the pale colouring of males in these and other harriers is discussed below.

  Fig. 3 Winter and breeding ranges of Hen Harrier in Europe

  Fig. 4 Winter and breeding ranges of Marsh Hawk in North America

  Nieboer considers that sexual dimorphism of plumage in harriers is a special adaptation to life in open country, of relatively recent origin. He stresses that it is most marked in the harriers of the Holarctic region; its occurrence in the South American Cinereous Harrier favours the argument that this bird derives from North America.

  No sexual dimorphism of plumage is found in the Spotted, Black or African Marsh Harriers and Nieboer considers that there is none in the Long-winged Harrier either. According to Brown and Amadon, however, the female of the latter species is most commonly browner than the male in the normal ‘light phase’ plumage. I have not seen any of the American harriers in life, but ever since I first saw a fine mounted specimen of the Long-winged Harrier in the Royal Scottish Museum many years ago, I have supposed this to be one of the finest members of the genus. With a wing length of over 480 mm in the largest females, it exceeds all other harriers in wing span. It is particularly handsome in the black, grey and white plumage phase and is described by Brown and Amadon as ‘unmistakable and beautiful as it beats its way slowly across the rich green of the pampas’.

  From my own field experience of the five European and Asiatic harriers I rate the Pied as the most beautiful. The species has been described as the eastern counterpart of Montagu’s Harrier, which it much resembles in its slim elegant form, and there is a very similar distribution of darker and lighter areas in the plumage of the adult males, the grey parts in the Montagu’s being mostly replaced by black in the Pied. The latter species is strikingly longer in the leg than other harriers in its size range, and Nieboer considers that this may be correlated with a preference for hunting wet terrain with high vegetation. The main breeding grounds of the Pied Harrier are in south-east Siberia but it also breeds locally in Burma and in North Korea. A huge intervening area comprising Central and South China may, according to Neufeldt, have been made unsuitable for them within historic times as their breeding habitats were converted into cultivated fields.

  Another very beautiful species must surely be the Black Harrier of Southern Africa. With its silvery underwing, white upper tail coverts and grey and black barred tail, the adult is really another pied bird. In both sexes of the Australian Spotted Harrier the slate-grey upper parts and chestnut below are spotted with white, but it lacks a definite white rump. It may perhaps be regarded as the most primitive type of harrier and is considered by Brown and Amadon to show affinities in plumage with the Serpent Eagles (genus Spilornis). The complicated group of Marsh Harriers has been divided into two species; the variable Marsh Harriers breeding in Europe, Asia, North Africa and Australasia, and the smaller, resident African Marsh Harrier. Anthony Buxton aptly described the Marsh Harrier as ruffianly in appearance, but an old cock is a striking bird, with silver grey on wings and tail contrasting with rich chocolate and orange-brown on his body and inner wing coverts. The flight is heavier, less buoyant-looking than that of other harriers—it is less dexterous at catching agile prey than Hen or Montagu’s Harriers—but it is capable of magnificient aerobatics when displaying in spring. In the eastern race C. a. spinolotus the male is even more eye-catching, with head, neck, upper back and underparts white, streaked with black. Some other races are much darker—one has a black form—while all the females and immatures are predominantly dark brown birds, usually creamy or whitish on the crown of the head.

  The reasons for the marked sexual colour difference in most harriers may be complex. The generally brown, rather inconspicuous colour of females has protective value when they are most vulnerable, on the nest. This adaptation probably arose during the early development of harriers when the birds nested in open country. The light-coloured and pied males are easily spotted by the human eye, particularly when they are making display flights, and this conspicuousness is certainly exhibited to the female during courtship. Jacques Delamain (1932) wrote of the male Montagu’s Harrier at this stage: ‘. . . the bird successively exhibits to his companion [the female] his light breast and the silvery underside of wings’. The conspicuousness of adult males of most harrier species, from above, is increased by the openness of the terrain which they frequent and by the high proportion of time they spend on the wing, and this is particularly true when breeding grounds are first occupied in the spring. The intensity of aerial display by paired males in colonial groups might suggest that a striking plumage pattern is either a stimulus or a deterrent to
other males.

  Some species of harrier certainly show little territorial exclusiveness, so it would be difficult to support this explanation for the plumage colour of males. That their striking patterns have value as some kind of signal I do not doubt and it may be important in this respect that harriers, unlike many eagles and falcons, tend to nest in comparatively featureless country without obvious perching places where they could be quickly spotted by others of their kind. Also, some harriers, notably the Pallid Harrier, have a strongly nomadic tendency, sometimes seeking out new breeding areas distant from those formerly occupied if, in spring, the latter are unsuitable owing to fluctuations in the population of major prey such as voles. The conspicuousness of the male Pallid Harier could well have an important signalling value in a nomadic search for areas with adequate food. It might be significant, in the same way, that the Rough-legged Buzzard, with its conspicuous black and white tail pattern, is much more nomadic in its occupation of breeding grounds than the usually more uniformly coloured Common Buzzard. It can hardly be doubted that the striking white tail base, which occurs in so many of the otherwise protectively coloured female or immature harriers, also acts as a signal and may assist in attracting other harriers to good food locations. I have often wondered how widely scattered harriers, many of which may be strangers to an area, succeed in finding a communal roost and it seems reasonable to suppose that newcomers must first observe the flight direction of established birds, and they may even be able to spot the white tail base of brown harriers at great distances.