The Hen Harrier Read online

  The underparts in feathered chicks of the Hen Harrier (see Chapter 1) are rich warm buff, streaked heavily with dark brown on the breast, more sparsely with red-brown below. On the underside of the wing the leading edge is bright salmon-buff, the axillaries and under wing coverts rich reddish buff, splashed with red-brown streaks, and the flight feathers are pale grey below, with a most arresting chequered pattern of dark brown wedge-shaped markings. I have described in Chapter 2 how the chicks can be sexed, when two to three weeks old, by iris colour and leg thickness. Female chicks are heavier and look altogether bulkier than males of similar age. As fledging time approaches, males are more inclined to escape into surrounding vegetation when approached, females tending to stay in the nest. Similarly, males usually fly sooner than females. During the last week or so before flying, the young harriers increasingly stand up on their long legs but they still sink back to rest ‘on their haunches’. The strength to hold down prey comes gradually, but well-grown chicks require judicious handling if laceration by their sharp black claws is to be avoided.

  Scharf and Balfour (1971) studied the growth of chicks and stated that the size difference between the sexes never obscured the size differences due to asynchronous hatching. Older chicks were dominant and so competed better for food. It was usually the latest hatched which succumbed to stresses of cold, rain and food shortage. They were surprised to find no difference in the pattern of development between young Hen Harriers in Orkney and young Marsh Hawks in Wisconsin, in spite of apparently greater hunting activity and more frequent feeding by the parents in Orkney. All those who have seen many nests of the Hen Harrier have found that the weakest chicks in broods often die in bad weather. There is sometimes presumptive evidence from picked remains that a chick which has died has been eaten by its siblings, and Balfour observed one female fly off with a dead chick, return with its decapitated body and feed it to the remaining chicks. Breckenridge observed a similar incident in the Marsh Hawk. Balfour thought it probable that chicks were sometimes killed by the female parent, or by their siblings, but he had no proof of this. Blake, however, said that he had seen ‘young males, almost fledged, plucked alive, killed and eaten by young females’. However, if the hierarchy in the nest is according to age, as Scharf and Balfour stated, there seems to be no reason why males should die or be killed by their sisters more often than the reverse. Weis and Buxton both recorded larger chicks of the Marsh Harrier killing and eating smaller members of broods; indeed Weis regarded this as usual behaviour in that species, but he found no evidence of killing, or even fighting, within broods of Montagu’s Harriers. It seems clear that in harriers, as in some other flesh-eating birds such as owls, cannibalism can sometimes ensure the survival of a proportion of a brood when there is a diminution of the normal food supply. Ingram (1959), commented: ‘it is eugenically preferable to rear, let us say, two or three well-nourished progeny rather than six or seven weaklings’, and further emphasised that ‘without a marked disparity in the age and size of the fledglings, fratricide would be virtually impossible’. The disparity, of course, is the result of the intervals between hatching due to incubation starting soon after laying has begun.

  The normal fledging date is between the thirtieth and thirty-fifth day. A single chick in a nest, which I watched from a hide, did not take its first flight until it was at least 38 days old (see Chapter 13). This was a male, although, as stated above, males can generally fly earlier than females; Scharf and Balfour, however, also recorded two single chicks which did not fly until the thirty-eighth day and concluded that they were too heavy to fly earlier; this was probably the case, too, with my male chick. Early fledging dates should be treated with caution; first flights may be hastened by human disturbance, and this may explain my earliest record of a chick which flew at 29 days. The average weight of chicks, at fledging time, is given by Scharf and Balfour as 472 grams, but female chicks may be as much as 100 grams heavier than males at this stage.

  Other behaviour of chicks

  Many aspects of chick behaviour are described in Chapter 13, and elsewhere in Part Two, the Study of the Hen Harrier in South-west Scotland.

  Hen Harrier chicks do not stray far from the nest, but from about the age of three weeks they often retreat a few feet into the surrounding vegetation and so form ‘hide-outs’ which provide shade, or shelter and some concealment. Balfour and Macdonald suggest that this habit also aids nest sanitation. As fledging approaches, they may spend much of their time just outside the nest and, as already described, they are sometimes fed at roughly-built platforms some metres from the actual nest. They are, however, much less prone to pre-fledging dispersal than the chicks of some other ground-nesting birds, such as Short-eared Owls. When closely approached by a human intruder the chicks vary in their reactions. Docile when very young, they soon begin to assume a menacing posture, with tongues lolling from wide-open mouths and wings half-raised as they stand their ground, or back slightly away, gazing fiercely at the intruder. Sometimes, on the other hand, even quite small chicks try to escape into hiding and half-grown chicks, especially males, may bound out of the nest. They will turn on their backs to strike with their claws if handled, but not with the rapidity of, for example, young Merlins.

  Breeding success and failure to breed

  In Orkney, Balfour and Cadbury found that the mean clutch size for 288 nests was 4.6; 60.5% of eggs hatched, 61.9% of chicks fledged; and the mean number of young reared for 223 successful nests was 2.5. My figures for much smaller samples in south-west Scotland are similar; a mean clutch size of 4.8, 57% hatching success, 60% fledging success and a mean number of 2.85 young reared per successful nest. In this region, however, nests in forests were significantly more successful than those on moorland (see Chapter 15).

  Balfour and Cadbury found some evidence that high fledging success (over 70% of young fledged) was associated with fine weather in June, but that there was little relationship between hatching success and weather conditions in May. They also considered the possibility that periods of low hatching success might be caused by organo-chlorine pesticides, as has been demonstrated by Ratcliffe (1969, 1970) for the Peregrine, but they found no convincing evidence of this for the Hen Harrier in Orkney. Bell’s analyses (pers. comm.) of eight livers and nine clutches of eggs of Hen Harriers in widely scattered parts of Britain are given in Table 3. He comments that, with two exceptions, the organo-chlorine residues in livers were all at ‘background’ levels and could have had little bearing on the deaths of the birds. The exceptions were numbers 347 and 1534, ‘where the dieldrin levels were exceptionally high and were undoubtedly responsible for the deaths of these two birds’. It will be noted that the number of clutches analysed is small and none is more recent than 1965.

  It may be said that there is no evidence that organo-chlorine pesticides have significantly reduced breeding success of Hen Harriers in Britain, or Ireland (Scott). Bell commented that the DDE residues in Hen Harrier eggs were considerably lower than those found in Sparrowhawks, in which species this metabolite has been primarily responsible for egg-shell thinning. There is, however, some evidence that in parts of Continental Europe breeding success in Hen Harriers has declined due to the effects of pesticides. Bijleveld (1974) mentioned a sharp decline of Hen Harriers in Sweden during the 1960s, in agricultural and forestry ground, due to pesticides; and also suggested that ‘agricultural pesticides’ may have been implicated in the complete breeding failure of five pairs in Marne, France, in 1970. In North America, Hamerstrom recorded a remarkable decrease of Marsh Hawk nests, from 25 in 1963 to four in 1965, on her study area in Wisconsin. By 1968 the decline had continued further. The paucity of nests was not associated with a comparable decrease in the number of adults on the study area during the breeding season. During the period of decline, birds showed abnormalities of behaviour; almost no ‘skydancing’ was seen and there was a marked increase in ‘almost frantic, talon to talon food transfers’. Hamerstrom speculated that an apparent lack o
f sexual drive, and consequent breeding failure, might have been due to the effects of pesticides possibly working through the avian component of the harriers’ diet. A recovery in breeding numbers reported by Hamerstrom in 1974 (per Newton) occurred, perhaps significantly, after a ban on DDT.

  In Britain, the possibility that pesticides have been implicated in some unexplained instances of apparent failure to breed cannot be discounted. In June 1973, Brian Turner estimated that there were some 20 pairs in one area of Argyll but concluded, after careful observation, that many of these did not have nests with eggs or young. In Galloway I have repeatedly noted that some pairs which have been present in spring either did not breed, or failed at an early stage, and then disappeared from the area; Picozzi has noticed the same behaviour in Kincardineshire. In all these instances, however, the explanation may be that the birds which failed to breed were unable to find adequate food in the area. It is possible that some moved on and found more favourable conditions to breed elsewhere.

  Balfour and Cadbury said that first year birds were less successful at hatching their eggs than older birds, but Hamerstrom found that they bred equally successfully. In south-west Scotland, of the four first year males, two failed to rear any young, suggesting a slightly higher failure rate than for older birds, but the difference is of no statistical significance.

  Nest failure at the egg stage is likely to be followed by a repeat laying in a new nest, often not far from the first. After later failures the birds usually disappear from the nesting area within a day or so. In these instances their whereabouts for the rest of the season may remain a mystery unless, of course, they are known to have been killed. In one case, in Orkney, an albinistic female which had unsuccessfully courted a male with two other females, was subsequently seen by Balfour living a solitary life on a different island.

  Age of breeding birds

  It has been known for a long time that some Hen Harriers breed in their first year. Gray (1871) was told that the male of a pair with young, shot in Sutherland by Crawford of Lairg, was in brown plumage and other first year males had been ‘repeatedly seen and killed at the nest’ by the same man. Harvie-Brown and Buckley (1884) stated that the male of a pair shot at the nest in Dunrobin Forest, Sutherland, in 1881 ‘had not attained adult plumage’. According to H. M. S. Blair (per Nethersole-Thompson) breeding by first year males was also noted in Norway from about 1885. Douglas first drew attention to instances among the Orkney birds (Nethersole-Thompson, 1932), and more recently Balfour has frequently found males and females breeding in their first year. Nevertheless, the proportions of these, in the Orkney population (13% of the females and 20% of the males) were considered (by Balfour and Cadbury) to be less than they would have been if all the surviving Orkney-born young of this age group had bred. It was also found that there were more breeding females above five years old than expected. A few were known to be nine or ten years old, and a female which was nesting in 1975 was twelve years old (Spencer pers. comm.). Balfour told me that one male was almost certainly aged thirteen. The age structure of the Orkney breeding population was considered by Balfour and Cadbury to lend support to the view that social behaviour was excluding some younger birds from breeding.

  I have found males and females breeding in their first year in south-west Scotland. I can give no reliable figure for females but four out of 47 males (8.5%) known to have nested were first year birds. In her study area in Wisconsin, Hamerstrom had 14 first year birds (male or female) among 46 breeding birds of known age (30%).

  Reactions to disturbance; predation on nests

  The spectacular attacking flights made by Hen Harriers against human visitors to nests have been the subject of much comment. It has been said that one or other parent is always aggressive in these circumstances, but this is far from the truth. I have found that at some nests neither bird flew nearer to me than about 35 metres, but the majority of females and a few males flew closer, at least when they had chicks. My notes of 34 nests show that attacks were pressed to the point of striking at only 13 (38%); at the other 21 nests aggression was mild or non-existent and, occasionally, females flew almost out of sight after rising from the nest. At 12 of the 13 nests the attack was pressed only by the female, and a very aggressive male was encountered at only one nest. At the majority of nests, males rarely came closer than about 45 metres. The same bird, of either sex, showed variations in degree of aggression at different stages in the nesting period. A few were highly aggressive at all times, but most reached a peak of boldness while chicks were under three weeks old. Interestingly, some males which had previously been quite timid dived fairly close, and were very noisy, when chicks were nearly fledged, attacking not so much near the nest as near the limit of the home ground which is defended, to some extent, against other harriers.

  Balfour found that about 50% of females, and a few males, were ‘aggressive’ in Orkney; and Peter Strang told me that about the same percentage of females in Kintyre showed some aggression, but only about two-thirds of these attacked strongly. Richmond thought that an old male with an inexperienced female was inclined to be more demonstrative at the nest than most, but the only very bold male I have seen, an old bird himself, was mated to an old, though timid, female. While examining a nest of Montagu’s Harriers, which kept their distance, Blake received repeated diving attacks from a male Hen Harrier. In contrast to the abundant evidence from Scotland that females are generally the chief defenders of nests, some American observers have found that the male Marsh Hawk is often dominant in this respect. Urner even said that all males were aggressive to human beings, and Saunders that the male was much more so than the female, though Bent found little difference between the sexes in this respect. Balfour believed, as I do, that the offspring of a bold parent tend to show similar behaviour when they breed; and it is certainly true that, even when newly fledged, young sometimes join a parent in her attacks, in apparent imitation. I have observed a female and her family diving at man and sheep in the nesting area. Similar diving attacks are made against foxes and other mammals on nesting grounds and at winter roosts (see Chapter 18).

  The results from my sample of 34 nests (Table 4) suggest that Hen Harriers which showed most aggression to man at nests were the more successful at rearing young. Nevertheless, one or two of the mildest females had outstandingly good nest histories over successful seasons, although one of these may have been fortunate, one year, in having a bold male as her mate. Richmond said that birds which were most timid towards a man at the nest were prone to desert at the slightest pretext. No doubt he was referring to desertions of eggs and, since I have generally refrained from visiting nests at this stage, to minimise risk of desertion, I am not qualified to comment from personal knowledge.

  An attack by a really bold Hen Harrier is at once a thrilling spectacle and an unsettling experience. It is thrilling because the bird displays its utmost mastery of flight, appears to be totally regardless of its own safety and presents a most exciting series of swiftly changing images to the eye. It is unsettling because the bird so obviously resents the intruder’s presence with every fibre of its being that, whether or not the intruder is physically discomforted by her buffeting, he is made to feel that he must retire as quickly as possible to allow the bird to regain her composure. These at least are my own feelings, but to their many human enemies the boldest birds are the most sacrificial. At first, after rising from the nest or its vicinity, the bird quickly gains height and flies away for 20 or 30 metres. Then she banks steeply, catching the light on the beautifully chequered undersides of her wings and turns, full-faced and yikkering, into the assault. She slants downward and assumes a strangely menacing outline, with broad wings angled sharply back from the wrists and wing-tips widely splayed. If her course is set low enough she will, certainly, rake a man’s scalp with her talons as she sweeps just above him and, presumably, it is the trailing hind claw which sometimes draws blood. More often, the clenched foot inflicts a thumping, quite startling blow
, but the speed with which the bird can turn and repeat the attack is its most devastating skill. This is most impressive when a bird continually varies the line and height of its approach, sometimes flying in so low that it seems about to strike a man’s face, but at the last second it always rises a little. Some of my own memories of these occasions are described in Chapters 10–12, but I particularly like Eddie Balfour’s story of the female harrier which lifted his beret and carried it 50 metres before dropping it in the heather. ‘I had an awful job finding it’, remarked Eddie, admiringly. Over the years I have noticed that a bird will unquestionably attack the man it knows—usually myself—in preference to a newcomer, and Eddie Balfour had the same experience. Once, at a nest with Ian Munro, who was visiting Orkney, he tested a bird by an exchange of headgear but after a moment’s hesitation the harrier ignored the familiar beret on Ian’s head and continued to attack the rightful owner. I suspect that this power of recognition lasts longer than a single nesting season. Aggressive birds often break off their attacks, temporarily, to perch and continue calling from the ground or from a tree and, in frustration, sometimes start to preen.