Studies of less familar birds 130. White-tailed Eagle By George Waterston Photographs bySvante Lmdgren, Christer Wastesson,]. F. Willgohs, Bjorn Bjornsson, ]6mas Sigurdsson, Uric Hosking andhea MacNally

(Plates 62-68)

INTRODUCTION FOLLOWING THE SUCCESSFUL re-establishment of the Osprey Pandion haliaetus as a breeding species in Scotland, there has been a certain amount of speculation on the possibilities of the return of the White-tailed Eagle Haliaetus albicilla to one of its ancestral haunts. From being at one time commoner than the Golden Eagle it became extinct as a breeding species in Scotland in 1916. Up to the middle of last century it held on in fair numbers in the west highlands and northern isles. The Isle of Skye appears to have been the main breeding stronghold with, according to Gray (1871), eyries on nearly every bold headland. Among sheep-farmers there has always been a deep-rooted antipathy to eagles; and in Sutherland, following the Highland Clearances and the development of intensive sheep-breeding, a ruthless war on the White-tailed Eagle ended in its complete exter­ mination in that county at the turn of the century. Although there was an unsuccessful attempt at an artificial reintroduction of a couple of young birds from Norway in 1959, and unsubstantiated rumours of others nesting, the species today is but a rare vagrant in the British Isles. The White-tailed Eagle ranges over a vast area of the north Pale- arctic region. It breeds in west Greenland, Iceland, and from Scan­ dinavia eastwards right across Russia to Mongolia and Kamchatka. To the south, it is to be found in East Germany and Poland, and in countries bordering the east coast of the Adriatic eastwards into Asia Minor. It formerly nested in the Faeroes where it is now only a vagrant. In 1954, a pair bred in Denmark after an interval of forty- two years. Voous (i960) deduced from its present irregular distribu­ tion that it probably inhabited the whole of Europe at one time. Unlike the Osprey, which re-established itself in Scotland as a result of migration between Scandinavia and Africa, the White-tailed Eagle is mainly a sedentary species. In Norway and Iceland, our nearest breeding areas, adults remain in their nesting localities through­ out the year, although the young may wander further afield. Even 458 WHITE-TAILED EAGLE STUDIES so, out of the 31 young White-tailed Eagles ringed in Norway up to i960, the longest distance travelled by any of the seven recovered was only a hundred kilometres. In Iceland, on the other hand, the im- matures seem to disperse over most of the country. In recent years, important surveys carried out in Norway and Iceland have added considerably to our knowledge. Between 1956 and i960 Willgohs (1961) organised an elaborate nation-wide enquiry into the distribution, population, ecology and breeding biology of the White- tailed Eagle in Norway. His paper is now unfortunately out of print, but a shortened version in Norwegian, published in 1963 in a more popular style and illustrated with distribution maps and photographs, is still available. In 1959 and i960 Ingolfsson (in press) carried out similar studies in Iceland; he has kindly sent me a summary of his unpublished paper. I am greatly indebted both to him and to Dr. Willgohs for permission to quote freely from their papers and from correspondence. In June 1962, assisted by a grant from the Royal Society for the Protection of Birds, my wife and I visited four eyries of the White-tailed Eagle in the county of Sogn og Fjordane in Norway with Dr. Willgohs.

IDENTIFICATION At moderate range in the field there is little difficulty in distinguishing an adult White-tailed Eagle from an adult Golden Eagle Aquila chrysaetos. The former's head and neck are much paler, and the shorter white wedge-shaped tail is a distinctive feature. At rest, it stands more 'hunched-up'; and if close enough one can detect the yellow iris (as opposed to the hazel iris of the Golden) and the great yellow bill with its deeper culmen. The yellow unfeathered tarsi and big feet are conspicuous. Adults become increasingly hoary with age and plate 63a (inset) shows how pale these older birds can become. In flight the White-tailed is more vulturine in appearance: the head is longer and the tail shorter in comparison with the Golden; in normal flight the wings are slightly angled, but in soaring thev are held per­ fectly straight and give the bird a very rectangular appearance (plate 67c).' Immature plumages are more confusing, particularly as it is the young Golden Eagle which has white on the tail (though this should not present any problems as it has a broad, dark band at the end). However, the young White-tailed has a uniform brown tail, lacking the dark bands of the adult Golden, and the same differences in shape and flight still apply (note the 'hunched-up' immature in plate 64b). At the age of eight to nine weeks the young W'hite-tailed is dark brown all over (plate 64a), whereas the young Golden, apart from having white

459 BRITISH BIRDS in the wings and tail, has begun to develop the 'golden' feathers on the crown and neck. The differences in the sizes and shapes of the bills of the two young eagles is well shown by a comparison of plates 66a and 66b; it should be added that for the first few years the voung White- tailed has a horn-coloured bill. The White-tailed Eagle's behaviour at an eyrie with young is very different. It is much more demonstrative when disturbed, and the pair will fly around overhead uttering their harsh cries. After a time, they may alight near-by to keep watch on an intruder—unlike adult Golden Eagles which usually disappear into the distance. In fact, they give the appearance of being much tougher and more aggressive.

POPULATION The survey by Willgohs in Norway showed that the White-tailed Eagle still breeds regularly in all the coastal counties northwards from Sogn og Fjordane to Finnmark. Of the 414 breeding territories known to have been occupied since 1850, 221 were certainly occupied in the period 195 6-1960, and 123 probably occupied; the remaining 70 were untenanted. In Norway the population density is highest in the coastal districts of Nord-Trondelag and Nordland, and on some outer islands from Troms to West Finnmark. Of the 344 pairs which probably breed annually, well over one-third are in Nordland. Will­ gohs illustrated his papers with maps showing the past and present distribution of breeding pairs, and from these one can see the contrac­ tion in breeding range and decline in numbers, particularly up to the 1930's. Eagles in Iceland have been legally protected since 1913, but are still occasionally destroyed by farmers. Poisoned baits laid out for Foxes Vulpes pulpes and Mink Mustela sp. have resulted in mortality among eagles; but Ingolfsson {in litt.) tells me that the use ot such baits was forbidden in the breeding range of the eagle in 1958 and that in the spring of 1964 an amendment was passed to the Act whereby all poisoning of Foxes and Mink was prohibited in the whole of Iceland for a trial period of five years. In 1890 there were probably around 150 pairs of White-tailed Eagles breeding in Iceland, but the present population is estimated at only about 20 pairs; they formerly bred in all districts and are now confined to the north-west. The decline in Norway is linked more directly with human persecu­ tion. Although government bounties for the destruction of eagles were withdrawn in 1932, certain district councils and game organisa­ tions still operate their own reward schemes. In the official figures giving the numbers destroyed annually, Golden and White-tailed Eagles are lumped together. In 1963 no less than 168 'eagles' were

460 WHITE-TAILED EAGLE STUDIES destroyed in Norway and a sum of £460 was paid out in bounties, equivalent to almost £z 15s. per bird. Further, between 1953 and 1963 the average number destroyed each year was 198. This heavy annual toll is a severe drain on the population. Willgohs considers that the White-tailed Eagle may soon be exterminated in the counties of Sogn og Fjordane and More og Romsdal unless protection is forth­ coming.

BREEDING HABITAT The White-tailed Eagle's broad tolerance of habitat requirements partly accounts for its wide distribution throughout countries of quite different terrain. The habitat must, however, provide nesting and roosting sites, and perches at moderate altitudes within a convenient distance of the sea or a large area of water. In Norway, the breeding habitat is varied. On low off-shore skerries, the nests may be quite accessible; most, however, are on rocky, mountainous and sparsely wooded islands, usually, as on the mainland, on inaccessible precipitous cliffs. There are only a few present-day records of inland breeding sites. Food availability is a vital requirement. As the White-tailed Eagle is not a specialised feeder, it can turn from one source of supply to another. It feeds mainly on sea-birds and fish, as well as on carrion in many forms. In Norway the great sea-bird cliffs probably influence its breeding distribution and density. Nest sites in both Norway and Iceland are varied. They are usually dry and well sheltered, often in corners or beneath overhangs. In high mountains, the lower cliffs or wooded slopes are chosen in preference to the upper levels, perhaps, Willgohs suggests, because of the climate at the beginning of the nesting season and because of their distance from the sea. In Norway nests above 300 metres are unusual. Of 98 sites examined by Willgohs, 84 were on ledges of cliffs, crags or slopes, eight were in trees and the remaining six on more or less level ground. In Iceland Ingolfsson has found nests in a great variety of places—on ledges or caverns in cliffs, and on rock columns to a height of as much as 75 metres. They may be on terraces on mountain slopes, on elevations in lava fields, or on small inshore islands (plate 67a), the smallest of which was only ten metres long, five metres broad and three metres high. Nest sites in Iceland are generally accessible; and at present all are found on the coast, usually within a kilometre of the shore. Formerly, there were breeding sites up to 90 kilometres from the coast, but these were always close to a river or lake. As in Nor­ way, nesting sites are highly traditional, though the same pair fre­ quently uses two or more within a territory. The oldest-known 461 BRITISH BIRDS nesting site in Iceland has been in use for at least 150 years.

FOOD Bannerman (1956) complained that disappointingly little was known of the food taken by White-tailed Eagles in Norway, but this gap has now been well filled by the detailed studies carried out by Willgohs. In fact, his work on the food is probably the most important single con­ tribution to our general knowledge of the species. In his 1961 paper Willgohs listed all the food items he had analysed, and then in his 1963 paper he brought the details up to date and summarised the whole in a 'prey-spectrum', an English version of which is reproduced here as fig. 1. This shows that, in an analysis of 1,044 food items, birds comprised 57.4%, fish 31.4% and mammals 11.2% of the total. It will be seen, too, that the Eider Somateria mollissima emerges as the most frequent prey species (see also plate 66b). In fact, birds figure largely in the food throughout the White-tailed Eagle's range in Norway, and in many districts they probably make ^ip the greater part of its prey throughout the year. Sea-birds are taken mainly in outer coastal waters, both afloat and ashore, commonly among the skerries and in the breeding season frequently near the cliffs which hold the big colonies. The commonest mode of hunting seems to be to catch diving sea-birds and ducks on the surface as they emerge to breathe. Young Kittiwakes Rissa tridactyla and other gulls are taken before they are fledged and adults may also be caught on their nests. Fish are secured in various ways. Live fish may be caught as thev swim in shallow water or near the surface. However, dead fish and fish offal are more commonly taken, these being the refuse from man's fishing activities or the remains left by gulls or Otters Lutra lutra. That the White-tailed Eagle is to a certain extent commensal with Otters was first remarked upon by Collett (1921), and Willgohs had this confirmed by several of his correspondents in both Trondelag and further north in Norway. Lambs Ovis and young Goats Capra have been found in prey remains, but it can seldom be stated categorically that such food has been obtained by kills of healthy individuals, and a number of cases have obviously involved ones already dead. It is significant that during his intensive field work Willgohs has never seen a White-tailed Eagle kill or even attempt to attack domestic animals; nor have these shown any fear of the eagles, though Sheep (and in several cases small lambs) have often been seen feeding in the immediate vicinity of eyries or favourite perches.

462 WHITE-TAILED EAGLE STUDIES

FIG. I. 'Prey-spectrum' of White-tailed Eagles Haliaetus albicilla in Norway, based on 1,044 Prey items (after Willgohs 1963). In the MAMMAL section 'Rumin­ ants' include Roe Deer Capreolus capreolus, Red Deer Cervus elaphus, Reindeer Rangifer tarandus, Sheep Ovis and Goats Capra, mainly young in carrion form, while the figure for 'Carnivores' is made up of Foxes Vulpes vulpes, Dogs Canis jamiliaris and Cats Felis catus

BIRDS (599 of 39 species) FISH (328 of 24 species) (a) Shag Phalacrocorax aristotelis 62 (k) Cod, Haddock, etc., Gadus spp. 90 (b) Eider Somateria mollissima 175 (1) Catfish Anarhichas lupus jz (c) Gulls Laridae 78 (m) Sea Perch Sebastes marinus 23 (d) Auks Alcidae 170 (n) Lumpsucker Cyclopteru's lumpus 77 (e) Other species 84 (o) Other species 49 (f) Unidentified 30 (p) Unidentified 17

MAMMALS (117 of 16 species) (g) Ruminants 58 (h) Carnivores 22 (i) Blue Hare Lepus timidus 10 (j) Other species 27

Willgohs stated, in conclusion, that the bulk of the information received from districts in Norway where the species was comparatively common clearly suggested that, in general, the White-tailed Eagle should be considered harmless to man's interests or at most a fairly unimportant predator of domestic animals.

463 BRITISH BIRDS In Iceland the present eagle population appears to feed mainly on Eiders, Lumpsuckers Cyclopterus lumpus, Fulmars Fulmarus glacialis, Puffins Fratercula arctica, Char Salvelinus alpinus and Trout Salmo trutta in that order. However, other food is readily taken if available; eagles are scavengers there to a considerable extent and are often seen feeding on dead Sheep and other dead animals.

BREEDING BIOLOGY In Norway nest-building has been recorded outside the breeding season and some nests may be partly built in the preceding year. The materials are usually collected by both sexes from loose matter near at hand, but sometimes they pull up rooted plants, in part with the aid of their wings. In one case, the two. birds were seen constructing the nest in turn. Additional materials may be carried in at any time during the breeding period. Ingolfsson remarked that, contrary to those in other countries, the nests of White-tailed Eagles in Iceland are very insignificant structures. They are often no more than a depression in the ground, lined with grass or moss; sometimes there are a few branches of birch Betula around the cup. Yet birch is abundant in the breeding range of the eagles in Iceland, so that there is plenty of potential nesting material around. The bulk of the nests in Norway are built mainly from dry sticks of birch, heather Calluna or juniper Juniperus, and the linings are of grasses, moss or fine heather. On remote islands off the coast, stalks of sea­ weed and bits of driftwood are also used. The size and yearly increase of the nests vary considerably; the biggest structures, up to ten feet in depth, were ones partly supported by small trees on slopes. Mutual display flight, mainly following a definite pattern, is often seen in Norway early in the season. Violent stooping in flight was rarely observed by Willgohs. Coition may take place on the nest or at some distance away, and Willgohs has watched and described several cases. In Norway egg-laying takes place from the beginning of March to the middle of May. It usually begins in March in the west and in parts of the north, but may be about a month later in east Finnmark. The White-tailed Eagle is one of the first birds to start laying in Iceland, the chief period being the latter half of April and the beginning of May. In Iceland, the average number of eggs in 14 clutches was 2.1 (range one to three). In Norway, in a total of 57 clutches, 5 had one egg, 40 had two and 12 had three, an average of 2.12 eggs per clutch; one pair in Solund had three eggs in each year from 1957 to i960 and there was a clutch of four in Vega in 1957. Willgohs supplied a lot of data on egg measurements in his papers.

464 WHITE-TAILED EAGLE STUDIES Of particular interest is the evidence produced by Willgohs con­ cerning the greater role played by the male in incubation and care of the young than has previously been asserted. Incubation begins when the first egg is laid. Extensive observations at one nest in 1957, 1958 and 1959 showed that both sexes shared incubation in the early as well as the later stages. Nest-reliefs did not follow any very regular pat­ tern. As with most other species of birds of prey, the female incuba­ ted throughout the night; the male then usually took over in the early morning, and in most cases had some further spells on the nest later in the day. Reliefs usually took place on the nest and averaged 5.8 per day. During the whole incubation period the male sat for 26.75% of the time. Willgohs estimated the incubation period in one case at 38 days (from laying of first egg to hatching of first egg). The interval between the hatching of the two eggs was about three days. Ingolfsson found that in 47 nests in Iceland where the young were well advanced (mostly well-feathered) the average number of eaglets per nest was 1.38, varying between one and three. Infertility of one of the eggs seems to occur fairly frequently; and, even if two or more young hatch, one of them often dies in the nest. Intermittent breeding is suspected, as the number of eaglets reared per pair per year in 37 cases was. found to average only 0.65. By comparison, Willgohs found that in 93 eyries in Norway, the number of young hatched averaged 1.6. There have been several cases of infertility of one egg, but natural mortality among the young seems to be low there and if it does occur is often caused by human interference at the eyrie. Most observers in the past have stated that during the fledging period the female takes over most of the domestic duties, the male rarely staying longer at the nest than necessary to deliver the prey. Willgohs spent long periods observing from hides and found that on occasion the male would not only feed the chicks but also brood them. At one eyrie, on a day when the young were three weeks old, food was brought to the nest three times in the early morning and once in the evening, on three occasions by the male and once by the female; feeding took place 11 times, at all times of the day between 04.46 and 20.45 hours, and each feed lasted from 2 to 22 minutes; of the total of 113 minutes of feeding, the male fed the chicks for 46 minutes. In Norway there is occasional hostility between White-tailed Eagles and Golden Eagles, with competition for nest-sites and food. Where they meet, the Golden appears to be dominant; but whether the dis­ tribution of the White-tailed Eagle is influenced by this remains uncertain. Juvenile or immature White-tailed Eagles generally seem

465 BRITISH BIRDS to be tolerated by adults in the breeding territories, sometimes quite near occupied nests.

REFERENCES BANNERMAN, D. A. (1956): The Birds of the British Isles.—Edinburgh and London. vol. 5. COLLETT, R. (1921): Norges Fugle (ved Orjan Olsen). Kristiania (Oslo), vol. 2. GRAY, R. (1871): The Birds of the West of Scotland. Glasgow. INGOLFSSON, A. (in press): 'The status, food and breeding biology of the White- tailed Eagle Haliaetus albicilla (L.) in Iceland.' Voous, K. H. (i960): Atlas ofTLuropean Birds.—Edinburgh. WILLGOHS, J. F. (1961): 'The White-tailed Eagle Haliaetus a. albicilla (L.) in Norway'. Arbok for Universitetet i Bergen, Nat.-Naturv. Serie No. 12. Bergen. (1963): Havomen. Bergen.

466 PLATE 62. Female White-tailed Eagle Haliaetus albicilla and two well-feathered young in a tree nest, Sweden; note the massive beak, projecting head, rectangular wings and short, wedge-shaped, white tail (pages 458-466) {photo: Svante Lundgren) PLATE 63. Above, adult White-tailed Eagle Haliaetus albicilla feeding large nestling, Sweden {photo: Christer Wastesson) and, inset, adult at rock nest with small chick, Norway {photo: J. F. Willgohs); both show the contrastingly pale head and bill. Below, well-grown youngster exercising, Sweden {photo: Svante Lundgren) PLATE 64. Above, immature perched on rock, Iceland; in its early years this species is dark brown all over and its bill is horn instead of yellow (page 460) {photo: Bjorn Bjornsson). Below, another in similar plumage standing at the edge of the water with characteristic hunched shape, Sweden (photo: Christer Wastesson) PLATE 65. Female White-tailed Eagle Haliaetus albicilla in heraldic pose at her tree eyrie with two young, Sweden {photo: Svante Lundgren) PLATE 66. Above, comparison of bills of young Golden Eagle Aquila cbrysaitos (left) and young White-tailed Eagle Haliaetus albicilla {photos: Lea MacNally and J. F. Willgohs). Below, adult White-tailed Eagle with dead Eider, Sweden; Eiders are regular prey in Norway and Iceland (pages 46Z-464) {photo: Christer Wastesson) PLATE 66. Above, comparison of bills of young Golden Eagle Aquila cbrysaitos (left) and young White-tailed Eagle Haliaetus albicilla {photos: Lea MacNally and J. F. Willgohs). Below, adult White-tailed Eagle with dead Eider, Sweden; Eiders are regular prey in Norway and Iceland (pages 46Z-464) {photo: Christer Wastesson) PLATE 67. Above, two young in a nest on a low-lying islet, Iceland; compare with rock and tree sites below and on plate 68 {photo: Bjorn Bjornsson). Below, a very different nest on hillside rocks, Iceland {photo: Jomas Sigurdsson); and flying adult showing heavy head, broad wings and white tail, Norway {photo: Eric Hosking) PLATE 68. Tree nest of White-tailed Eagle Haliaetus albicilla high in a pine, Sweden {photo: Christer Wastessori). Inset, a bulky cliff eyrie in Norway showing the lining and the normal clutch of two white eggs (page 465) {photo: J. F. Willgohs)