Studies of less familar birds 147. Cory's Shearwater By Francis Roux and Christian Jouanin (Plates 20-22)

Various changes have been made in the scientific nomenclature of Cory's Shearwater since the publication of The Handbook of British Birds (1938-41). Not only has the specific name kuhlii been replaced by diomedea, in accordance with the rale of priority, but, following the osteological work of Mayaud (1932) and Kuroda (1954), the re-estab­ lishment of the genus Calonectris, between Procellaria and Puffinus, has been proposed (Alexander et al. 1965). Thus it is by the scientific name of Calonectris diomedea—and no longer Puffinus kuhlii or Procellaria diomedea—that the species is designated in most recent works. Its biology and status are not much better known than they were 30 years ago, however, because research into these aspects has not advanced to the same extent that it has with, for instance, the tubenoses nesting in the British Isles, such as the Manx Shearwater Puffinus puffinus and Fulmar Fulmarus glacialis. Lockley (1952) and Bourne (i955)made the principal contributions to knowledge of the geographical variations and nesting habits of Cory's Shearwater. More recently, Pickering (1959) and Jouanin and Roux (1966) described what is probably the largest colony in the Atlantic, that on Great Salvage between the Canary Islands and Madeira; in this connection, we also summarised information obtained on the biological cycle, and usefal data on breed­ ing in the Azores were given by Mallet and Coghlas (1964). With a wing span nearly equal to that of a Lesser Black-backed Gull harusfuscus, Cory's Shearwater is the largest of the tubenoses breeding in Europe. But the Great Shearwater Puffinus gravis of Tristan da Cunha, whose range outside the breeding season covers the north Atlantic and which in summer passes through European -waters, is hardly smaller and generally rather similar, so that the separation of the two species is not always easy. At a distance, Cory's looks a large shearwater with long wings, a moderately long wedge-shaped tail, almost uniform grey- brown upper-parts (including the head) and immaculate white under- parts. At closer range, the lighter edges to the mantle feathtQs, especi­ ally in fresh plumage, make the whole mantle look paier than the wings (plate 22) and the under-surface of the wings riiows a grey border (plate 20). There are never dark markings on the axillaries, flanks and belly, nor does Cory's have the pale collar and dark crown of the Great Shearwater. In that species a deep brown crown contrasts sharply with

163 BRITISH BIRDS a pale nape and a pure .white throat; Cory's has no pale zone separating the crown from the mantle, and the hood extends on to the side of the neck to shade off gradually into the white of the throat and hreast (plate 20); this presence or absence of a cap and white side-neck is probably the best quick character for distinguishing the two species. Although visible only at rather close ranges, the strong, yellowish bill (plates 21-22) is a certain identification feature, as that of the Great Shearwater is blackish and noticeably more slender. A white V-shaped mark above the tail, generally lacking in Cory's, is illustrated in numerous identification books, including A. Field Guide to the Birds of Britain and Europe (1954), as one of the distinguishing features of the Great Shearwater. In fact, the observation of this character alone is not sufficient for identification in the field, as many Cory's show a noticeable white mark at the base of the tail (plate 22): the upper tail-coverts are often pale-tipped and so contrast with the dark brown tail. The frequency and extent of this white mark seems to vary not only among individuals and with the state-of the plumage, but also between races and even populations of the same race. Hun­ dreds of individuals observed by Nisbet and Smout (1957; 201) in autumn in the eastern Mediterra­ nean showed no trace of it. Yet not Great Shearwater "Puffinus gravis, off less than 30% of the Cory's Shear­ Cape Clear, Co. Cork, September 1965 waters of the Madekan archipelago (see a!so pages 145-159). Note the clear-cut cap, white side-neck and and Salvage Islands have suchamark dark bill which distinguish it from above the tail in the summer. As Cory's Shearwater {phot): K. W. Perry) this large Atlantic race C. d. borealis appears off British and Irish coasts at the same time as the Great Shearwater, it is therefore necessary when seeing a shearwater with a whitish rump to examine the head pattern and bill coloration,before deciding the species. The nature of the flight •is also an important character, as Cory's does not fly in the same manner as the other shearwaters of European seas: its wing beats are notably slower, its glides longer sustained, its action less of a 'flutter and glide'. In calm weather it glides for long distances on bowed wings, giving from time to time two or three heavy flaps. An important character is that the tips of the wings are held below the horizontal of the body in gliding. In rough weather the ease

164 CORY'S SHEARWATER STUDIES and freedom of its action are suggestive of an albatross Diomedea spp. rather than of the more laborious flight of other shearwaters. In these circumstances it can be distinguished at a distance from the Great Shearwater, as Dr. W. R. P. Bourne (in Palmer 1962) has noted, 'by great height to which it rises when towering into wind, so that it appears above horizon, and the appearance of a pure white belly as it turns to resume downwind glide*. It is, in fact, rare for the Great Shear­ water, whose low skimming flight resembles that of the Manx Shear­ water, to rise much above the waves. Cory's Shearwater frequents the Mediterranean and north-east Atlantic, and comprises three distinct subspecies. The characters des­ cribed above apply principally to the European forms: the Mediter­ ranean C. d. diomedea, of intermediate size, and the North Atlantic C. d. borealis, which is larger. Apart from the size difference, which is very noticeable in the hand, these two subspecies are inseparable in the field. The third subspecies, C. d. edwardsti, frequents the Cape Verde Islands in the eastern tropical Atlantic. It is distinctly smaller than the first two, and can be distinguished by the darker coloration of its upper-parts (centre of back as dark as wings), by its weaker beak which for the most part is blackish and not yellow, and by its longer and more square-cut tail. Although probably a migrant like the others, as it is absent from the Cape Verde archipelago in winter, this form has not been recorded north of the tropics. The typical race nests in the Mediterranean from Spain to the Adria­ tic, the Balkans and Asia Minor as far as the Bosphorus, mainly on small offshore islands. The best known colonies are on the Balearic Islands, on certain islets off the coasts of Mediterranean France and Corsica and Sardinia, and on the island of Zembra in the Gulf of Tunis. Much less information is available on the size and exact location of colonies in the eastern Mediterranean: these are mainly in the Aegean, on the coasts of Turkey and in Crete, but not in Cyprus. There are no nesting records from the east and south Mediterranean coasts between Turkey and Tunisia. In autumn this race migrates to the Atlantic and from the Straits of Gibraltar extends down the coasts of western and southern Africa. It occurs in abundance to the south-west of the Cape of Good Hope from November to March and is a vagrant as far as the eastern coasts of the United States, where specimens have been col­ lected off Long Island and the Florida Keys. The one British record of this race has now been discarded with the Hastings Rarities (Nicholson and Ferguson-Lees 1962); nevertheless, it is not unlikely to be encoun­ tered in British waters as k has been taken on the north coast of Brittany and on the North Sea coast of Germany. The North Atlantic race C. d. borealis, distinguished by its larger size and rather stronger beak, breeds on the Berlengas off Portugal, in the

i6S BRITISH BIRDS Madeiran archipelago (on the Desertas and on Porto Santo), on Great Salvage, in the Canary Islands (mainly on the eastern group) and in the Azores. Its non-breeding range extends westwards to the North American coast, off which it is particularly common from August to November, and north-east to about 50° north. It is now recognised annually in varying numbers off Ireland and in British Atlantic seas. Vagrants also occur more rarely in the North Sea and the English Channel. It has been recorded once in the Netherlands and once in the south Baltic. There is little doubt that this North Atlantic race pene­ trates the southern hemisphere, as it has been recorded from the coast of Brazil. Its occurrence off South Africa is only recently confirmed; earlier records there have been attributed by Dr. W. R. P. Bourne to the Mediterranean form (Palmer 1962). Contrary to former opinion, founded on an error in the labelling of two specimens collected by Ross's Antarctic Expedition in 1840, the species is unknown in the Indian Ocean (Bourne 1955). It is in February-March that the adult Cory's Shearwaters return to their breeding localities, both in the Mediterranean and the Atlantic (the annual cycle of the different populations seems identical). Habitu­ ally silent on the high seas, they then become excessively noisy, especially on dark nights, and their calls disclose the whereabouts of the colonies. It is probable that the name 'Cagarra', given to the Cory's Shearwater b) Portuguese fishermen, is derived from its raucous and powerful voice. Described as a 'bubbling wail', a 'moaning' and a repeated 'horrible rasping cry', the call can be transcribed as ia-gow-a- gow-gow in sonorous gutturals. Other cries, written as ia-ia-ia, have been attributed to the females, but this requires verification. Cory's Shear­ waters repeat these cries during aerial evolutions which precede landing in the colony (plate 20) and on the ground at the time of nest relief. In general the volume of sound is particularly intense during the two hours following sunset and diminishes gradually thereafter, but builds up again at the end of the night; it stops completely at first light and the brooding birds are silent throughout the day. In large colonies the chorus produced by hundreds calling together is truly deafening. On the isolated rocky islands and coastal cliffs where they form their colonies, Cory's Shearwaters are very catholic in their choice of incuba­ tion chambers. Less given to digging than typical shearwaters, they prefer to occupy natural cavities which the eroded and volcanic rocks of the Atlantic islands offer in large number. On Great Salvage every crevice and hole of sufficient size can shelter a nest (plate 21a). Some­ times the hole is large enough for the sun to penetrate (plate 21b) or for several pairs to take up their abode. These shearwaters also nest in ruined human habitations as well as in the soft earth of the plateau where they will sometimes excavate actual burrows. On the French 166 CORY'S SHEARWATER STUDIES Mediterranean islets they sometimes do not seek shelter other than that provided by vegetation and there nest in 'galleries' under thick scrub (A. Rivoire in lift.). They frequently decorate their nests with pebbles, shells, bones or vegetable debris (plate 21b). It may be that these materials, which are sometimes in considerable quantities, arise from architectural necessity: when the ground slopes steeply, the building of a platform of pebbles assures a horizontal surface for incu­ bation (Jouanin and Roux 1966). For none of the three races have the incubation and fledging periods been established, nor the age at which individuals start to breed. It is known only that the clutch is laid generally at the end of May or in early June, that the first chicks are hatched at the end of July, and that the young begin to leave the nest at the end of October. As the adults are present at their nesting places from the end of March, the repro­ duction cycle extends over seven months. But the events which make up this cycle—laying, hatching and fledging—appear to be much more synchronised than in other shearwaters: on Great Salvage the spread of dates between the laying of the first and last eggs in the colony does not appear to exceed three weeks and all the young fly within a similar period. As is the rule among the tubenoses, the clutch consists of a single egg, which is white. Male and female incubate in turns, but the length of each spell on the nest is unknown. The return of those coming to relieve their partners may begin well before sunset, at least in the colonies free from human disturbance, such as .that on Great Salvage; this contrasts with the exclusively nocturnal behaviour of other shear­ waters and may be connected with the robustness of this species which on oceanic islands has little to fear from natural predators. But on islands where fishermen persecute them, the Cory's Shearwaters do not come to land until it is quite dark. On their return from the fishing grounds, they assemble on the sea in sight of the colony; resting on the water in flocks like ducks, they await the moment for coming to land. Protracted aerial evolutions in front of the cliffs then precede the land­ ing, which gives the impression of not always being successful at the first attempt. On hatching, Cory's Shearwater chicks are covered with grey-brown down and weigh 70-80 grams. At first they are brooded by one of the parents, but after a few days (how many ?) they are left alone in the nest and visited only for feeding at night. According to Mallet and Coghlan (1964: 123), the second grey down appears about the tenth day, the tail feathers after z\ weeks, the secondaries after 3! weeks and the pri­ maries after four weeks. On 9th September a chick seven weeks old had secondaries 70 mm. long—which suggests that it would not have been able to fly for several more weeks—and weighed 960 grams. (The weights of adult Cory's Shearwaters vary from 700 to 1,000 grams.) 167 BRITISH BIRDS The rhythm of the feeding visits of the parents is still unknown, as are the circumstances of the last feeding of the young before they fly. Only one brood is reared annually. In this species, which has markedly gregarious behaviour, social factors appear to play a large part in the breeding activity and pro­ bably cause its synchronisation. These factors may also explain the scattered distribution in certain archipelagos where some islands are densely colonised while others, apparently quite as favourable for breeding, are uninhabited. Dense colonies may go on attracting peri­ pheral breeders and thus militate against spread to other islands. In the Madeiran archipelago the species is subject to commercial exploitation, which is not unreasonable as it is exercised only at the expense of young ready to fly. For more than a century 18,000-24,000 young have been taken annually on Great Salvage; their flesh is salted for selling in Madeira, while their down is used for making eiderdowns and their oil for the upkeep of brass fittings on boats. To encourage breeding, and to assist exploitation, the hunters used often to build crude walls or piles of stones in which the shearwaters readily nested. Unfortunately, in addition to this controlled exploitation, these shear­ waters have for some years suffered from the depredations of fishermen whose visits have been facilitated by the mechanisation of their fleets and who do not hesitate to seize adults and eggs. For this reason the population of the Desertas, quite close to Madeira, and the islets of Porto Santo, js certainly much smaller than it was about 30 years ago when Lockley (1952) visited these islands. On Great Salvage itself the number of young collected over the last four or five years has appreciably diminished and everything suggests that the present annual cropping now exceeds the replacement capacity of the population. Of the known colonies of Cory's Shearwater, that of Great Salvage is probably the largest. Before its recent diminution it was estimated at a minimum of 22,000 pairs, as this number represented the average ann­ ual culling of chicks. The true total, however, was certainly well in excess of 44,000 birds since there must have been a margin of breeding success to perpetuate the colony and since account must be taken of the numerous non-breeders. Unfortunately, no estimates exist regarding the strength of the colonies on the Azores, the Canary Islands and the coasts of Portugal (C. d. borealis), on the Cape Verde Islands (C. d. edwardsii) or in the Mediterranean (C. d. diomedea). As far as the last race is concerned, a large colony is known on Zembra Is­ land, off Tunisia, and recent observations also suggest the existence of important colonies in south-west Sardinia (C. Erard verbally). In conclusion, we should like to express our gratitude to P. A. D. Hollom for translating this text from French into English, and to Dr. W. R. P. Bourne for useful comments on it. 168 CORY'S SHEARWATER STUDIES

REFERENCES ALEXANDER, W. B., et at. (1965): 'The families and genera of the petrels and their names'. Ibis, 107: 401-405. BOURNE, W. R. P. (1955): 'On the status and appearance of the races of Cory's Shearwater Procellaria diomedea'. Ibis, 97: 145-149. JOUANIN, C, and Roux, F. (1964): 'Une mission aux iles Salvages'. Science et Nature, no. 61: 1-8. (1966): 'La colonie de Puffins cendres Calonectris diomedea borealis (Cory) de Selvagem Grande'. Bol. Mus. Mun. Funchal, XX, Art. 89: 14-28. KURODA, N. (1954): On the Classification and Phylogeny of the Order Tubinares, particularly the Shearwaters {Puffinus). Tokyo. LOCKLEY, R. M. (1952): 'Notes on the birds of the islands of the Berlengas (Portugal), the Desertas and Baixo (Madeira) and the Salvages'. Ibis, 94: 144-157. MALLET, G. E., and COGHLAN, L. J. (1964): 'Cory's Shearwater Procellaria diomedea breeding in the Azores'. Ibis, 106: 123-125. MAYAUD, N. (1932): 'Considerations sur la morphologie et la systematique de quelques Puffins'. Alauda, 4: 41-78. NICHOLSON, E. M., and FERGUSON-LEES, I. J. (1962): 'The Hastings Rarities'. Brit. Birds, 55: 299-384. NISBET, I. C. T., and SMOUT, T. C. (1957): 'Field-notes on some birds of south-east Europe'. Brit. Birds, 50: 201-204. PALMER, R. S. (1962): Handbook of North American Birds. New Haven and London. vol. 1: 155-160. PICKERING, C. H. C. (1959): 'Note sur le Puffin cendre (Puffinus diomedea borealis) aux iles Salvages'. Oiseau, 29: 1-3, plate 1.

169 PLATE 20. Cory's Shearwater Calonectris diomedea returning from the sea in the evening, Great Salvage Island, July 1963. It is calling, with the result that its throat is distended and its bill partly open. Note the head-colour shading into white under-parts, and the grey-edged under-wing (pages 163-169) (photo: F. Roux)

PLATE 22. Cory's Shearwater Calonectris diomedea flying low over the breeding ground just before landing, Great Salvage Island, July 1963. This illustrates the strong, yellowish, dark-tipped bill, the mantle paler than the broad wings, and the variable white mark above the longish tail (pages 163-164) {photo: F. Roux)

PLATE 21 {left). Upper, at rest after landing in the evening; the nest is in the hole under the rock. Lower, adult brooding in a narrow rounded cavity completely sheltered from above, but into which the sun shines; note the pebbles and debris which build up the nest (page 167). Bill and head are shown well {photos: F. Roux)