The Hen Harrier Read online

  Over a large part of its breeding range—in northern and eastern continental Europe and Asia, and much of North America—Hen Harriers are absent in the winter. Bent reported that the males returning from the south reached Manitoba in mid-March, as much as three weeks ahead of the females, while Hamerstrom found that males arrived on the nesting grounds in Wisconsin about the same time, and the females followed 5–10 days later.

  In the less severe winters of western Europe, Hen Harriers hunt over some breeding grounds in any month, but these individuals may or may not include those which nest there. Certainly, in Orkney, a few ringtails, wingtagged there in summer, have been seen roosting not far from the nesting grounds in winter. In Scotland generally, there does not appear to be the same clear-cut distinction in arrival times of males and females in the nesting territories as has been found in regions where the species is fully migratory. In south-west Scotland I have the impression that males visit the breeding areas increasingly on fine days in February and March, and these may well be birds which will breed there. On one such day, about the middle of March, a pair may be seen together, lazily floating above the territory where nesting took place in the previous year. They may not appear until early April or even later, but the first pre-nesting flights of the pair do not seem to be delayed by cold weather. Balfour found that pairs were also seen over the nesting grounds in Orkney in March, and he did not indicate that males preceded females there. On 18 March 1976, I visited a forest in south-west Scotland where there had been three nests in 1975 and found that a pair were already flying conspicuously above the old sites, in very cold but sunny weather. Sometimes they drifted apart but during the afternoon the two birds, in their beautifully contrasted plumage, kept near together for long periods, the cock most often a little above the hen. This is characteristic behaviour at the pre-nesting stage. Now and again the cock loses a little height, dives playfully at his partner who may turn on her back, or he touches her, wing to wing. From afar, silhouetted against the pale cerulean sky, the birds are like tiny arrow-heads, only distinguishable by the bulkier form of the hen and the occasional flash of silver-grey as the cock wheels in the gentle sunlight. They glide on tense wings, rising and falling almost imperceptibly. Time seems to stand still for them. As they work slowly over a wide expanse of forest or moor, they are not hunting but appear to be scrutinising the ground in which the nest will later be sited. On breezy days they lean into the wind on sharply flexed wings, their long tails often fanned and for ever in motion. At this early date they separate towards evening, no doubt to seek a meal before dusk, but in early April I have seen a pair settle to roost not far apart, very close to a nest of the previous year. On warmer days they soar together to a great height, with wing tips almost in contact, until the watcher strains to keep them in sight through binoculars. Jacques Delamain referred to similar ‘magnificent and calm ascensions’ by a pair of Montagu’s Harriers. Yet, at any time in early spring, the advent of stormy weather, or more especially a blizzard, will drive them away from the nesting grounds and they may not be seen for days.

  I have seen the first tentative versions of the full display flight before the end of March. This, surely one of the most arresting of all avian displays, has been most aptly christened ‘skydancing’ by Frances Hamerstrom. At first the male, after spiralling upward a little, angles downward only to rise and fall again in a series of undulations. There is nothing spectacular about these trial runs, but an observer might be forgiven for wondering if this can be the same bird which has previously behaved with such quiet restraint. The wing tips taper sharply to points, so that the outline is quite different from usual, more like a large wading bird as it whiffles down to land on a still day. The contrast between the black wing-ends and the white under-parts is revealed to the maximum. The combination of this pattern and the uninhibited manner of the undulating display flight, often remind me of the spring flight of the Lapwing. For many days, until well into April, the most heady ‘skydancing’ is likely to be withheld. In its most intense form it consists of a steep climb, for perhaps 30 metres or more, when the bird rolls on its side ‘like a wing-nut turned on a bolt’ (Breckenridge), or turns a somersault followed by a seemingly reckless earthward dive which is suddenly checked, just above the ground, either by the start of another ascent or by flying slowly onward to alight, often at a possible nest site. In fine weather the performance may be repeated many times—the exceptional number of 105 successive dives was once recorded by Balfour. All the time the wings are flapped rather slowly and loosely, as if the bird were acting in a trance. At no time is a harrier more conspicuous. In this way it may advertise its presence to other Hen Harriers by displaying over several different possible nesting stations, travelling from hill to hill and rising high above each in turn. Although some of the most prolonged display flights are made by young unmated males, or by males whose mates have died or been killed, ‘skydancing’ commonly takes place when one or more females are in the vicinity. It is most intense when two or more pairs or polygynous groups are nesting within sight of each other, and my own experience indicates that when pairs are separated by a few kilometres the full display is not likely to be seen at all. Hamerstrom discovered that a number of different males ‘skydanced’ during April over the same site and, when a pair finally nested there, the male was not one of the ‘skydancing’ birds. Typically, however, the behaviour is quickly followed by the inspection and selection of the nest site. Females often display, also, ‘especially when they outnumber males’ (Brown, 1976), but according to Balfour their flights usually take a ‘switchbacking’ course rather than one of steep ascents and descents, as I, too, have noted. The hen usually watches her displaying mate from the ground and it may be that the display helps to establish a bond between the pair, but it does not appear, from what I have said, to play an indispensable role for pairs in isolated situations. Once, when three other Hen Harriers were in the vicinity, Balfour saw a male and female ‘skydancing’ together. The male’s aerial display generally ceases about the time that eggs are laid, but according to Brown (1976), diving displays by females continue late into the fledging period.

  Flight path of ‘skydancing’ Hen Harrier

  During display and courtship both sexes call frequently. Display flights are often accompanied by bursts of chattering (‘yikkering’), similar to the alarm calls made when a nest is threatened, but not as loud. The female’s ‘yikkering’ is high-pitched and was compared by Walpole-Bond to the trilling of a Little Grebe. Frank L. Beebe (1974) writing of the Marsh Hawk, gives a good rendering of the call as ‘kek-kek-ke, check-quik-ah-ek’. The male’s version is distinctly lower-pitched, but I once heard a first year male’s call that was almost as high-pitched as his mate’s. It is, however, the squealing whistle (or ‘squeal-wail’) of the female which is the dominant sound during the courtship period. Transcriptions of this sound hardly agree in more than assigning it two syllables. At different times I have written it ‘swee-uk’ and ‘twiss-you’, and it may vary in different situations. It is best-known as a begging call, urging the male to release food which he is carrying, but it also solicits copulation during courtship and may be continued with piercing insistence as the female follows the male about the nesting ground. The complementary call by the male, typically given when he approaches with prey, is a much quieter and lower-pitched ‘dyouk-you’ or ‘tchiou’—almost a chuckle—but I have occasionally heard a male give a loud ‘swee-uk’ call when he was, perhaps, frustrated by a female refusing to come to take food from him. On one such occasion the male’s call sounded to me like a sharp bark. It is obviously difficult or impossible to be sure, from a long distance, which bird is making a particular call and this has no doubt led to incorrect statements by some writers that the ‘swee-uk’ call usually comes from the male.

  The following passage translated from the French of Delamain describes a facet of courtship which is unknown to me and does not seem to have been observed by others: ‘. . . t
he Hen Harrier . . . mimes, to pay his court, a carving scene. Taking a stand on a clod of earth, not far from his female, he repeatedly lowers his hooked beak towards his empty talons, as if he were mangling a prey then, standing erect again, exhibits his white breast’. He compares this to other well-known examples in which male birds exhibit prominent features of their plumage to females, such as the cock Chaffinch showing his ‘white epaulettes’.

  The food pass and copulation

  About the time that the nest site is selected and building begun, the male begins to supply food for the female. At first he may fly in with prey but no aerial transfer or ‘food pass’ ensues when the hen approaches him. She may assert herself by dispossessing him of his prey after he has landed with it. On such occasions he appears very much the weaker partner but she will very soon be totally dependent on his hunting skills for all her food, which she will receive by the food pass. She will, however, continue to hunt for herself to some extent until she has begun to lay and incubate the eggs. Possibly, the male’s first presentations are important in providing extra nourishment at the time of egg formation.

  After a brief period of hesitancy, the food pass is nearly always achieved unerringly. The cock approaches, usually with the prey held in his conspicuously lowered foot, but sometimes carried pressed back under the tail. His manner of flight varies from a calm slow glide to steady almost hurried flapping. Very often he first comes into view a little above the horizon of the nesting hill and slowly loses height until he is almost above the nest. These never fail to be moments of tingling expectancy as the watcher waits for the hen to rise. If incubation has begun, and sometimes even before the start of laying, the nest can be approximately located by noting where she breaks cover at the start of her short flight to take the food pass or, of course, by watching for her return afterwards. During incubation she usually stays off the nest for some minutes while she feeds, and she may take a brief flight before returning to the eggs. The details of the food pass have many variations but in its most usual form the cock, keeping slightly above and ahead of the hen, drops the prey which she catches in an outstretched foot. This is achieved either by turning on her side or completely over onto her back, but she rights herself so swiftly that it is often difficult to be sure from a distance precisely how the catch has been made. Sometimes the prey is exchanged, talon to talon, and occasionally the hen takes prey from the cock on the ground. Later in the season, particularly when the chicks are near to fledging, hens often fly further from the nest—as much as 400 metres—for the food pass. Balfour saw a female take prey from the male, by a food pass, even though she was already carrying prey herself, but Dickson commented that the male in a similar situation flung his prey in the air so wildly that the female failed to catch it.

  It is tempting to regard the food pass as a ritual, perhaps preserving the bond between male and female through the long period when their separate roles, as hunter and guardian of the nest, permit hardly any other contact between them. Yet, I wonder, is it not reasonable to suppose that the habit of aerial food exchange developed simply as the most efficient method for birds nesting in extremely tall dense cover, sometimes in marshes, where prey, which is usually small, would be easily lost if it were dropped to the ground? Obviously, too, the long legs of harriers are advantageous for exchanging prey in the air. Presumably, the nest would run a greater risk of predation if the conspicuously plumaged cock habitually brought food for the hen directly to it.

  Balfour wrote that coition will follow almost every food presentation until the sexual urge has been subordinated by that of brooding. He described the sequence of events as follows: ‘After the “food pass” both birds will be grounded and perhaps about 50 yards apart. Instead of getting on with her meal, the hen crouches over it, giving vent to the food call with more urgency than ever. She is soliciting the male and he will respond unless he is not yet ready to do so.’ The act of mating takes place on the ground, near where the nest will be built, or is already being constructed. It is accompanied by wing flapping of the male as he maintains his balance on the female, while she crouches with half open wings and raised tail. Food presentation, however, by no means invariably precedes mating. Of Montagu’s Harriers, Delamain wrote that ‘during two weeks and almost at every bringing of prey the nuptial rite will be the same, always provoked by the female after the food offering, and barely solicited sometimes, with sharp cries or an impatient flight, by the male’. I have observed a female Hen Harrier which had not been brought food before mating, continue to give begging calls afterwards, perhaps urging the male to hunt for a meal!

  Surprisingly, Hamerstrom very rarely observed copulation in her long study of a breeding colony. I imagine that this was because the terrain where she worked was much less open than Orkney and birds on the ground more difficult to see. I have found, in south-west Scotland, that the only occasions when I could observe this behaviour clearly were when the birds were in open moorland. Those nesting in forest plantations are so often hidden by trees when they land that many details of their behaviour can only be surmised. In this habitat copulation is most likely to take place in forest rides.

  Nest building

  I have already mentioned that the cock at the end of a display flight may land in a possible nest site, where the hen follows him. When, in April or early May, the pair are to be seen slowly cruising close to the ground, with tails widely fanned, it is often the cock which drops first into a patch of tall vegetation. Nor is it rare for him to carry nest material at this stage. It is interesting to learn, according to Neufeldt, that the cock Pied Harrier glides above the hen with a small twig in his feet and is dominant in the selection of the nest site. Yet there is general agreement that the final choice of the nest site is made, and nearly all the building done, by the female Hen Harrier. It is not difficult to tell, from a distance, when nest-material rather than prey is being carried. Small bundles are sometimes carried in the bill, larger ones in the feet. Long strands of grass for nest lining trail most conspicuously beneath the tail, or like straggly moustaches from the bill. Balfour considered that Walpole-Bond’s description (1914) of the female nest building could not be improved upon: ‘sometimes she walked rather clumsily for a short distance, sometimes she would jump rather curiously in the air [‘endeavouring to uproot some heather’ comments Balfour]; otherwise she indulged in low flights of a few yards and alighted again. Eventually she tore off a thin rod of ling, then flew by a circular course, low down and in a rather guilty manner, to a certain area of tall heather, into which, hovering momentarily, she let herself down gently.’ Nest materials are all collected from within a couple of hundred metres of the nest. I have watched a hen make eight short flights to collect material in half an hour. Often, a nest is begun and abandoned for a different site, and at this stage the birds are easily upset by anyone misguided enough to walk over the ground in search of a nest.

  The nest and nest sites

  Although Hen Harriers’ nests are generally built among tall vegetation, it is remarkable how open the actual site often appears at close quarters; this may be partly because the birds do a certain amount of trampling in preparing the site, but I believe they choose a small, relatively clear space at the start. The material most commonly used for nest building is heather, varying from stout twigs to fine stems and sprays. Many nests are partly made of old bracken stalks and I have also found twigs of birch used. In my own district, however, few nests are close enough to birch trees for these to be used commonly. Balfour also found old withered thistle and foxglove among nest material.

  In two out of four Irish nests in plantations of Scots pine or spruce, described by Garry Doran (1976), the foundation was made largely of gorse. Heather was a component of all four nests. Other materials used were straw, birch, larch, spruce, bracken and a little grass. This basic material is loosely woven together. A softer lining is then added, usually of grasses or rushes, often mainly the papery strands of dead molinia grass; sometime
s bracken alone is used. Woodrush, the Golden Eagle’s favourite, is also used as lining by some Hen Harriers. All through the nesting season the hen sometimes adds material, both to the outer structure and to the lining. Until the chicks are three or four weeks old, nests usually look quite clean and there is often an attractive contrast of colour between the dark outer material and the pale yellow or orange grass in the lining. The neatest nests have a ‘soup-plate’ appearance, but are often very flat with hardly any depth to the cup. I noted that one nest, poorly built by a first-year female, was made almost entirely of grasses. Some are much bulkier, ‘at least ten inches high’ according to Balfour. He gives the diameter as, generally, thirteen to twenty inches (32.5–50.0 cm)