Flight patterns of the European bustards

Transcription

1 Flight patterns of the European bustards By Vhilip J. Stead THE BUSTARDS, as a family, are terrestial birds and spend the major part of their time on the ground, but both the Great Bustard Otis tarda and the Little Bustard O. tetrax frequently indulge in short flights and take to the air readily if approached. Being a desert species, the Houbara Bustard Chlamydotis undulata is less inclined to fly than the other two, preferring to crouch. However, in flight all three have continued... 43

2 BRITISH BIRDS distinctive wing-patterns which enable them to be identified at a considerable range. Few British bird books contain illustrations of any of the bustards on the wing. The revised edition of The Popular Handbook of British Birds (1962) figures the male and female Little Bustard in flight on page 172, whilst A Field Guide to the Birds of Britain and Europe (1954) shows the Great Bustard in flight on plate 26. However, this latter illustration, as several ornithologists familiar with the Great Bustard have pointed out, is not entirely accurate and I am told that it has unfortunately not been possible to correct the plate in the forthcoming revised edition of this work. It was felt, therefore, that it might be helpful to illustrate the wing-patterns of these three species together, in the light of existing knowledge. The accompanying drawings of the Great, Little and Houbara Bustards are based on field sketches made in Austria, Spain and Suffolk respectively, but the extensive skin collections at the British Museum (Natural History) and the Liverpool Museum have also been examined. On the wing, the male Great Bustard is unlikely to be mistaken for any other species. The bird is heavier and deeper-chested than a Mute Swan Cygnus olor and has longer wings, which are held down-curved like those of a Heron Ardea cinerea. The wing beats are powerful but slow, about the same speed as those of a Heron, the wings beating through a fairly shallow angle both above and below the horizontal. The female Great Bustard is smaller and looks about the size of a Grey Lag Goose Anser anser in the air. The wing patterns of both sexes are similar a broad white band along the upper primaries and secondaries running almost the full length of the wing, the trailing edge of which is black. As with the Little Bustard, the primary coverts are surprisingly long and the dark tips form a patch on the leading edge of the wing. The Little Bustard is much smaller and looks about the size of a Mallard Anas platyrhynchos on the wing. Indeed, in sustained flight or when rising from the ground the bird can appear rather duck-like as it flies with its neck extended and the wing action is similar to that of the Mallard. On the breeding ground, where the Little Bustard does not normally fly any distance, the wing beats are usually shallower and mainly below the horizontal, the wings being held decurved like those of a Red Grouse Lagoptts lagoptts. In level flight the bird has a tendency to glide, merely flicking its wings downwards at intervals which emphasises the grouse-like effect. The male can have a swollennecked appearance at times, particularly if flushed whilst displaying. His wings also make a distinctive whistling sound, which perhaps serves to alert other bustards in the vicinity if the birds are feeding in tall herbage and out of sight of each other. This sound, which is 44

3 Flight-sketches from side and rear of (top) Great Bustard Otis tarda, (right centre) female and male Little Bustard 0. tetrax and (bottom) Houbara Bustard Chlamydotis undulaia (drawn by P. J. Stead) 45

4 BRITISH BIRDS audible at some distance, may be caused by the peculiarly short and emarginated fourth primary, an adaption which is unique in the bird world. Except for the coverts the wings of the Little Bustard appear largely white in flight, although there is a black area on the forewing formed by the tips of the primary coverts and the leading four primaries. The visible portion of the first primary is black for virtually its full length, but when the bird is in level flight and the primaries are not fully spread this may be obscured so that there appear to be two separate patches of black on the wing. The male also shows a white rump and in breeding plumage the neck pattern contrasting with the grey head is visible at a considerable range. The Houbara Bustard has three races which show much variation in both size and colour, particularly of the back and tail. The Asiatic race C. u. macqueenii, to which all the British records refer*, is the largest and palest of the three. In size, males of this form approach that of the female Great Bustard, but the wing pattern of the Houbara is quite different, the primaries and secondaries being largely black with a prominent white patch on the forewing. The pale grey greater and median coverts form a band across the wing, the lesser coverts and back being sandy brown, finely vermiculated with black. In flight, seen from the rear, the wings are kinked at the carpal joint like those of *H. E. Axell in his note on the Suffolk Houbara (Brit. Birds, 5 7: ) concluded that subspecific identification of this individual was impossible because of a number of conflicting characters. This conclusion was based on the description of the African race C. u. undulata in R. Meinertzhagen's The Birds of Arabia (1954: 548) and that of the Asiatic race C. u. macqueenii in The Handbook and J. A. Murray's The Avifauna of British India and its Dependencies ( : 575). Having examined the large series of skins of all three subspecies of the Houbara in the British Museum (Natural History) only a week after seeing the Suffolk bird, I must beg to differ with Axell's view, as I am quite certain that this individual belonged to the Asiatic form, macqueenii. The much broader and coarser bands of black on the mantle of undulata give it an altogether darker appearance which alone is quite sufficient to distinguish it from macqueenii. In fact, the two races are so dissimilar that at one time they were considered to be separate species. In the light of Axell's note, R. Wagstaffe kindly examined the Houbara skins in the Liverpool Museum collection. Both the number of tail bands and the amount of white on the neck plumes (the conflicting characters referred to above) vary in both forms and Wagstaffe does not consider that cither could be used to separate the two races. On the other hand, all the skins in the Liverpool collection can be separated at once by the colour of the long feathers on the fore-neck, which are grey in macqueenii and white in undulata, and by the black feathers on the crown of macqueenii, which are absent in undulata. The black crown feathers were very prominent in the Suffolk bird and are mentioned in Axell's description. At least one of the previous British specimens, that shot near Redcar, Yorkshire, on 5th October 1892, is still in existence, being preserved in the Hancock Museum, Newcastle upon Tyne. It is a typical macqueenii and almost identical with the Suffolk bird, including the absence of any white on the neck plumes. 46

5 FLIGHT PATTERNS OF BUSTARDS a Stone Curlew Burbinus oedknemus and the wing pattern is, indeed, reminiscent of this species. The wing action, however, is much slower, the strokes being through a fairly shallow angle both above and below the horizontal. Like the Little, the Great and Houbara Bustards extend their necks in flight, which in their case accentuates the rather goose-like effect of the slow wing beats. I should like to thank the authorities at the British Museum (Natural History) for allowing me to examine skins of the bustards and R. Wagstaffe at Liverpool Museum for the same facility and for his help and guidance on several points. I am also grateful to I. J. Ferguson- Lees, P. A. D. Hollom and D. I. M. Wallace, who read this article in draft and made many helpful suggestions. 47