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The Hen Harrier Page 10
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There is considerable agreement among older writers about one of the Hen Harrier’s methods when hunting Partridges. Daniel, in his bloodthirsty but uproarious Rural Sports (1807), must have been one of the earliest propagandists against Hen Harriers. He advocated setting pole traps for ‘ringtails’, placed in specially set ‘bird bushes’ into which the hawk was sure to drive a covey of Partridges, then perch on the pole while seeking them out. Jardine said: ‘I once shot an old female which had driven a covey of Partridges into a thick hedge and was so intent on watching her prey that she allowed me to approach openly from a distance of half a mile’. In this century, Dugald Maclntyre (1947) described how a pair of Partridges with a brood escaped from a Hen Harrier by hiding under a thorn bush. In each case it might be more correct to say that the Partridges sought safety in the cover of bush or hedge, rather than that they were deliberately driven there.
Hen Harriers do not habitually seek prey by hovering at a height, as Kestrels, Rough-legged Buzzards and sometimes Common Buzzards do, but they frequently check themselves in their progress, to hang, with beating wings and spread tail, at three to six metres above the ground. This low level hovering can be seen when a harrier is hunting over crops or other dense ground cover where small birds or mammals may be concealed. Hovering over bands of reapers, for the ‘game’ disturbed, was noted long ago in south-east Scotland (Muirhead, 1889).
As a group, harriers are the most owl-like of hawks in their hunting methods. Short-eared Owls and Hen Harriers each sometimes suggest the other by their behaviour and outline when hunting, though the harrier’s smaller head and much longer tail are quite diagnostic, and the long tail is almost as mobile as a kite’s. Harriers are also more like owls than other birds of prey in having large ear apertures, about as big as their eyes, and it might be expected that these would facilitate crepuscular hunting, which Neufeldt frequently observed in the Pied Harrier, but there is not much evidence that this occurs in the Hen Harrier. Certainly, in my own experience in Scotland, I have never observed it in summer; and in ten years of observation at winter roosts I have only seen rather desultory hunting by birds at about sunset, and none at all in near darkness. Breeding adults normally cease to bring prey to their young about an hour or two before sunset and, in winter, hunting grounds are deserted for the roost within about a quarter of an hour before or after sunset; in other words, before the light is really dim.
Hen Harriers are not very early risers in the morning. Though some will leave a winter roost in dim light they do not usually start to hunt immediately. Brown and Amadon suggest that the harriers’ sharp hearing serves them in locating small animals such as mice by their squeaking and rustling, when sight alone might not detect them in the cover of long grass. I have seen Kestrels hunting much later in the dusk than Hen Harriers and it seems evident that the relatively larger eyes of falcons render them more capable of crepuscular hunting. Indeed even small birds such as Robins, which continue feeding long into the dusk, are endowed with conspicuously large eyes. St John, however, noted Hen Harriers hunting rats in rickyards at dusk. When, on one occasion, a hunting Hen Harrier passed within a few feet of the car in which my wife and I were sitting, we were quite able to hear the ‘swoosh’ of its wings, whereas an owl at the same distance would have been inaudible.
When censusing raptors in Michigan, the Craigheads discovered that Marsh Hawks were often not spotted because they spent so much time on the ground. The time averaged 57% of the day and was higher in wet weather, when a pair were on the wing for only half an hour in three hours. Heavy rain probably makes normal hunting almost impossible, by hampering both vision and hearing, while prey is also less active and more skulking. When such conditions occur, persistently, while chicks need food, the smaller or weaker members of broods sometimes die from starvation. I have, however, seen prey brought to nests in moderately heavy rain, and Schipper records that, in one long spell of rain, 16 items of prey were brought to a Hen Harrier’s nest while, in the same period, nothing was brought in by Montagu’s Harriers. He also found some indication that high wind velocity, by itself, was advantageous for hunting Hen Harriers. Both Hen and Montagu’s Harriers brought a higher proportion of birds among their prey in strong winds. Louis Urquhart has told me that the spectacular capture which he observed in Arran (see here) was made on a very windy day. In such conditions manoeuvrability in hunting may be greatest. It would be interesting to know how far spells of really bad hunting weather threaten the survival of Hen Harriers in winter. It might be expected that inexperienced, first year birds, which certainly have much higher mortality than older birds, would be at greatest risk.
Hen Harriers frequently perch on posts, bushes or stone dykes and no doubt these are used as an aid to spotting prey, but they hardly make any use of high perches, such as telegraph poles, which Kestrels, Buzzards and owls find convenient aids to hunting. In America, the Craigheads recorded some hunting from perches by Marsh Hawks. In Galloway, R. C. Dickson has seen a female Hen Harrier on the ground, prowling the heather, apparently stalking fledged young Meadow Pipits. It seems likely that some nestlings and beetles are located while the harrier is on the ground. I have watched a female Hen Harrier moving about in a willow bush, where a Reed Bunting was perched in the lower branches. The harrier was unable to flush it out and could not come to grips with it in the bush.
Many observers, past and present, have said that the Hen Harrier could be seen travelling the same route at approximately the same hour for days in succession. Seton Gordon (1923) wrote that one in the Outer Hebrides was so punctual that he could almost set his watch by it. Collectors and keepers killed birds by waiting for them to appear at the expected time. The date and time of over 200 winter sightings in Galloway have been collected by Louis Urquhart and myself but very few of these indicate such regularity. Certainly, a male feeding young often brings prey within half an hour or so of the same time daily, particularly in the late afternoon, but he may not follow the same route. The only occasions in our experience when birds repeatedly followed the same line at nearly the same time, were when they were travelling to and from winter roosts, but the same general areas, as much as twelve kilometres from a roost, were visited by hunting birds over many winters. At times, almost certainly, the same individual hunted the same area over a period of days or weeks.
Sometimes several individuals hunt in close proximity on particularly good feeding grounds. R. C. Dickson has seen up to five together, in winter, hunting two kale fields, of 85 hectares, where unsuccessful attempts ‘by bursts of speed’, were made to take Curlews, Pheasants and Wood Pigeons on the ground. It is not uncommon for two or three hunting Hen Harriers to be in view at once, in autumn or winter, where voles are abundant. K. W. Bartlett has told me of a remarkable observation of five males disturbed together from the edge of a young conifer plantation, in Galloway on 3 January. As the birds were seen at about 11.00 hours there was no possibility of a roost-gathering, and they were presumably attracted by food, although a search of the ground provided no obvious explanation.
It is not uncommon for Hen Harriers to become involved in encounters with other predators over prey. My own most interesting experience in this respect concerned a Merlin and a male Hen Harrier on a September evening, over a flat moorland near where both species roosted. It occurred well before dark and both birds were in search of food. At first the Merlin was merely diving at the low flying harrier but when the latter flushed two small birds, probably pipits, the Merlin cut in below it and pursued one of them upwards above the harrier which continued as before. The small bird evaded the Merlin by slanting towards the ground but by ill-luck its path took it within reach of the harrier which grasped it in an outstretched foot just clear of the heather without hesitating in its flight. The Merlin reacted with something very like fury at being baulked, buzzing the harrier at full speed when it landed with its prey. I had the impression that the Merlin, which was in attendance on the harrier for about half an hour, may ha
ve shadowed it deliberately on the chance of snatching flushed prey.
Very similar observations have been made by David Bates and Dr R. J. Raines in Cheshire, in winter. It was noted that a Merlin and a ringtail Hen Harrier were often in the air together, and closer study showed that as the harrier quartered the ground the Merlin circled above and stooped at any small birds which it flushed, whereas the harrier attacked birds which had dived to the ground after being flushed by the Merlin. Don and Bridget MacCaskill (1975) describe how a female Hen Harrier suddenly appeared, flying swiftly towards a Short-eared Owl, and robbed it ‘neatly’ of the prey it was carrying. Eddie Balfour recorded Hen Harriers in Orkney robbing Short-eared Owls and Kestrels of prey and once saw one in pursuit of a Merlin carrying prey.
In Co. Kerry, Frank King several times saw a male Hen Harrier make a fierce attack on a male Kestrel as it crossed the harrier’s home ground on its way to and from its own nest near by. Frank King writes: ‘The harrier would rise like a silver streak to intercept the Kestrel and both birds would fall down into the heather like a madly-flapping feathered ball, all wings and tails, tightly locked together. The first time I saw this happen I thought the harrier intended lunching on Kestrel, but after about a minute of silence (the birds out of view on the ground) they both flew up, the harrier now holding the mouse the Kestrel had been carrying’. He adds that both the harrier and Kestrel successfully reared young. Piracy by Hen Harriers on such neighbouring predators may be no commoner than similar acts by Kestrels on Short-eared Owls and, occasionally, harrier, Kestrel and owl are seen competing for a particular victim, as recorded by R. C. Dickson (1971).
Many pairs of Hen Harriers have Short-eared Owls as close neighbours and sometimes Merlins or Kestrels as well. It appears that both in winter and summer such associations can be mutually advantageous in the location of prey. Eddie Balfour told me that he had seen a female Hen Harrier dispute with a Peregrine over a Mallard which the latter had killed. Although the harrier was forced to retire at one stage, it returned to take possession of the kill and feed upon it. Nick Picozzi has seen a female harrier snatch food from another female in spring; Balfour’s and Picozzi’s observations were both made in Orkney.
Hunting habitats
The Hen Harrier hunts almost any kind of open or fairly open terrain which supports high numbers of birds or mammals small enough for capture. Woodland is generally avoided, except where the trees are mostly less than about six metres high, or are interspersed with comparatively open ground. The most common hunting habitats are moorland and heath, bogs and marshes, sand dunes, cultivated fields, rough pasture and young conifer forests. Scrub woodland, such as willow, birch or juniper is also hunted. Fernando Hiraldo writes that, in south-west Spain, wintering Hen Harriers particularly hunt the maquis of rock rose (cistus) and heather, and also exploit barren deforested ground. Very open ground, such as mown hayfields and stubble, are favoured seasonally, especially when exposed prey suddenly becomes vulnerable.
The Hen Harrier’s hunting grounds show a wide altitudinal range. In good vole years it can find enough food at 1,000 metres in the Norwegian mountains, but in some parts of its breeding range, such as Britain, food scarcity above 600 metres confines it to lower elevations. In great contrast to the high Norwegian fjelds are the Dutch breeding grounds in the Flevo polders and on the Wadden Islands. W. Schipper finds that it hunts over meadows, dunes, cultivated fields, saltings and marshland; in Flevoland the numerous wintering Hen Harriers mostly hunted open fields when voles were abundant but, when these declined in numbers, more birds were taken from the marshes.
In Britain in winter, Hen Harriers range much more widely over lowland fields, marshes, saltmarshes and sand dunes than in summer, but upland moors and young conifer forest are by no means deserted. In the Scottish Highlands ringtails are much commoner in winter on moorland than adult males. In Galloway, where many adult males as well as ringtails winter, the range of habitat hunted at this season is wide. My analysis of sightings of hunting birds (see Fig. 12) between September and March, indicates a gradual shift to hunt lower ground as winter advances. In the lowlands of Galloway, favourite winter hunting grounds are marshes and agricultural land, especially weedy fields of turnips or kale, which attract high numbers of likely prey in the form of small birds, particularly finches and buntings. There is some indication that, at this season, males form a higher proportion of the Hen Harriers hunting open fields than they do in other habitats with taller vegetation. In the Netherlands, Schipper found that females, in the breeding season, tended to hunt ‘more structured vegetation’ than males.
In North America the Marsh Hawk occupies an equally wide variety of habitats but in the absence of other species of harrier, is a more important predator in deep marshes.
Food
In some parts of the Hen Harrier’s range, mammals form a larger part of its prey than birds, although a higher proportion of the latter tend to be taken in summer than in winter. Several studies of the prey of the Marsh Hawk in North America have shown the great importance of small rodents in its diet. The Craigheads (1956) found that, in winter, Marsh Hawks on Michigan farmland preyed chiefly on meadow mice, which made up 93% of the prey items in 1942, and 99% in 1948, even though mice were less abundant in the latter year. They were still the major prey in spring and summer, at 54.9%, but small and medium sized birds amounted to 31.4% in these seasons, when much less data was obtained than for winter prey. It was noted that as vegetation grew in the spring the mice became less vulnerable. At a comparable latitude in Western Europe (about 47°) there would not be the same scarcity of possible bird prey in winter.
Randall’s study (1940) of the seasonal food habits of the Marsh Hawk in Pennsylvania, showed that ‘mice’ were the staple food in every month, except June and July, when juvenile birds were the most important items. More than 60% of the total yearly food items consisted of ‘mice’ (? voles). This study was done on a ‘pheasant range’ and it was found that only 9 out of 829 items, (1.1%) were pheasants, all apparently juveniles. Randall commented that a large part of the avian prey was probably taken as carrion, or after the young had been exposed by the activities of man (mowing and harvesting). Errington and Hamerstrom (1937) had reported that they found no perceptible relation between the conspicuous hunting activity of Marsh Hawks and the seasonal shrinkage in size of pheasant broods. Errington and Breckenridge (1936) found some regional variation in summer prey, in different parts of the prairie country of north and central USA. In Iowa prey was almost equally made up of birds and mammals while in Wisconsin mammals (mostly ground squirrels and young cotton-tail rabbits) greatly predominated, at 81% to 14% birds, mostly passerines. Errington and Breckenridge tabulated nearly 1,000 items of prey in all. Those of minor importance included frogs and insects, the latter appearing in twice as many pellets of juveniles as of adults.
Less data were obtained on prey at other seasons as few harriers wintered in the region. They fed mainly on mammals in the cold months and often fed on carrion. Even in the fall, most observed feeding was on roadside carcasses, mainly of rabbits; and in winter the staple food consisted of mice and frozen carrion, with a few weak Bobwhites. Other studies confirm the impression that in North America the Hen Harrier feeds most on small mammals and that small birds are also important prey in spring and summer. Clayton M. White writes that it may take higher proportions of bird prey in the southern parts of its American breeding range, and reports that in Utah it relies heavily on recently fledged passerines, especially Horned Larks.
The Marsh Hawk has a traditional reputation as a killer of poultry and game and has been much persecuted on this account. Prey investigations have produced no real evidence to justify this. In one of his studies, in Minnesota, Breckenridge (1935) made the interesting comment that most of a small number of pheasants and chickens taken were the prey of one particular pair of hawks which were not the nearest to the poultry. He added that all the farmers in the vicinity seemed to recognise the
effectiveness of Guinea Fowls and Purple Martins in protecting their poultry from hawks, and that the farmer reporting hawk damage had neither of these about his premises, whereas one or the other was present on all the other farms. Two almost full-grown American Bitterns were rather surprising prey found at a nest in saltmarsh, by Charles A. Urner (1925), who commented that young Bitterns were no mean antagonists. In Norfolk, England, Anthony Buxton (1946) often saw the larger Marsh Harrier dive at Bitterns but did not think that they ever dared to attack them in earnest. Urner did not mention the strong possibility that such prey was taken as carrion. Although most of the bird prey identified by American ornithologists consisted of passerines, other birds taken included rather many flickers (woodpeckers) whose slow flight and habit of feeding on open ground evidently made them vulnerable. Among curiosities of prey, no less than eleven Crayfish were found among 63 items at a nest in Arkansas (Wilhelm, 1960). It will be noted that fish have also been recorded as food in Britain.
In Europe, the bulk of the Hen Harrier’s prey is divided between mammals and birds and, as in America, the proportions vary both regionally and seasonally. Hagen’s list of summer prey in the Norwegian fjelds, quoted by Bannerman (1953), gives a total of 333 mammal items and 228 birds, or 57% and 41% respectively of the whole, but no account is taken of prey weights. The mammal most commonly taken was the large mountain vole (Microtus ratticeps) and nearly all the mammal prey consisted of small rodents. Many species were identified among the birds and about a third were pipits and finches. A much smaller number of birds as large as Fieldfares, or waders such as Golden Plover and Wood Sandpiper, occurred, and the few grouse and duck were nearly all young. Bannerman says that the list included all the smaller birds of the fjeld. Nevertheless, Hen Harriers in the Norwegian mountains are rarely able to find enough food for all their chicks in years when the vole population is low. During the period covered by Hagen’s list (1938–46), at least four of the years were good for voles. In Finland, Hen Harriers are considerably dependent on the fluctuating population of lemmings.