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is coolest, visibility is at its best, and it is then that birds drop down to investigate any- thing that immediately relieves the monotony of the desert. Isolated outcrops of rock and cairns attract these migrants yet are themselves dangerous, for so often they are already tenanted by snakes or falcons. The drifting sands below their whitewashed ledges are often littered with the skeletons and wings of those birds seeking rest, On this and other journeys I found wings of Willow Warbler Phylloscopus trochilus, White- throat Sylvia communis and Subalpine Warbler Sylvia cantillans beneath such sites, though this pair of breeding falcons had yet shown no signs of feeding on the early migrants.

Around Gebel ’Uweinat and the Gilf Kebir, which support a small nocturnal insect and mammal population, the falcons are crepuscular, though in times of migration are still active after dawn. Throughout September, at Wanyanga in the southern desert, I have watched them hawking Trident Bats that emerge in vast numbers at dusk beside the lake.

As a breeding bird in the Libyan Desert the Sooty Falcon seems to be confined to the broken hills and scarps on the southern borders of the Sand Seas, and again in isolated hills in the desert to the south. The Sand Seas cover a hundred thousand square miles of desert and offer few suitable sites for the falcons. In early September I have seen a pair in the barren rocky hills a hundred miles north of Sarra well at lat. 22”30’, N., and two pairs later the same month as far south as lat. 19” N. in the region of Wanyanga. One of these pairs was almost certainly rearing young in the eroded sandstone cliffs to the east of Wanyanga Saghir, a small oasis depression in the extreme south of the Libyan Desert.

Von Heuglin in his ‘ Ornithologie Nordost-Afrikas’ (1869) records small colonies of this rare falcon breeding in July and August on the rocky islands in the southern part of the Red Sea. However, I think it most unlikely that more than two pairs of these desert falcons would ever breed in close company. Their ecology is clearer than it was, though we are now faced with the remarkably interesting problem of why the Sooty and Lanner Falcons should breed at correspondingly different times of year in their range across the Libyan Desert.

20 October 1960. B. D. McD. BOOTH.

[Derived, as they are, from colour transparencies, the author deprecates the reproduction of the photographs (Plate 2), but in view of their unique interest, it has been decided to publish them. This seems to be only the second report of the nesting of the Sooty Falcon, the first for nearly a hundred years, tnd perhaps the first in the continent. (The statements in Meinertzhagen, ‘ Nicoll’s Birds of Egypt : 374 and ‘ Birds of Arabia’: 346 leave some doubt.) It is now evident that autumn migrants travelling over the eastern Mediterranean and the eastern Sahara are liable to run the gauntlet first of the Aegean Eleanora’s Falcons and then of the Sooty Falcons in the desert. That two species which are allopatric should have the same adaptation to breed at a time when almost all other species have produced fully fledged young, and should depend €or food on these birds as they migrate, seems without parallel among Palaearctic birds. It is the more remarkable because probably no land- birds anywhere breed in conditions that involve greater strain on their water economy than is experienced by these Saharan Sooty Falcons. Since Wingate found them in the desert in the early spring and Booth found them in the same area in late summer it is possible they may be resident there; but if so it is difficult to imagine how they maintain life in the midst of such utter desolation when there are no migrants upon which to feed.-E~.]

SPRING MIGRATION OF RAPTORS IN BULGARIA The migration of large birds of prey across the Bosphorus has been described by

Nisbet & Smout (‘ Ibis ’ 1957 : 483-499). Some of these migrants are thought to follow the Black Sea coast on their passage into Europe.

On 27-29 March 1960, with Dr. Boev of the Zoological Institute of Sofia, I visited the Burgas region, especially the shallow lakes and salt pans which lie to the north, west and south of the town-lakes Atanosov, Burgas and Mandra. The last of these is

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normally ' out of bounds ' to foreign diplomats, and I visited it by kind permission of the Bulgarian Ministry for Foreign Affairs. Our main objective was the aquatic avifauna, but during these days we witnessed a considerable passage of raptors, amounting to several hundred birds. We did not attempt a specific count, but made the following observations.

The weather was fine but rather cold, with sea mist during the first two nights and temperatures near freezing, and during the day a light steady breeze from the east. Our observations were made mainly between 10 a.m. and 5 p.m. Migrants were flying low to moderately high and the general direction was north-west to west. They passed singly, in groups, or in continuous streams lasting up to 15 minutes.

The most numerous species were the buzzards (Buteo buteo, with a few B. lagopus and B. rufinus) the kites (Milvus migrans and a few M. milvus), and the harriers (Circus aeruginosus, and three C. cyaneus). Also seen were one adult male of Haliaetus albicilla and a number of other unidentified eagles, among which was probably Aquila heliaca.

At the Burgas Lake in the middle of the day a continuous stream of these raptors was seen in company with flocks of Cranes Megalornis grus, and White Storks Ciconia ciconia. There was a considerable migration of herons Ardea cinereu. This association of species had been observed by Boev in previous years. Rooks, Corvus frugilegus, were also seen in large flocks, immature birds predominating.

The westerly direction of the migration appears to be confirmed by four facts: (a) Boev's observations mentioned above were made near Yambol, 50 miles due west of Burgas; (b) on 29 March we observed a flock of 38 Cranes in a marshy area near Lozenets a few miles north of Yambol; (c) we observed very few raptors along the coast north of Burgas, although a stretch of 25 miles was covered thoroughly, and ( d ) I had observed earlier in March one adult male of Circus aeruginosus a few miles east of Sofia at the foot- hills of the Balkan range, and about 200 miles due west of Burgas. It is suggested, therefore, that the migration route follows the Black Sea coast as far as the Bay of Burgas, and there turns west towards the ' Balkan Corridor ', i.e. the valleys running east/west on the south side of the Balkan range.

Indications that this may be an important migration route for other species were provided by observations made at the beginning of May 1960 a few miles to the east of Sofia, where the Corridor emerges into the Sofia Basin. These included: White Stork, two separate groups of about 60 birds; Black Tern Chlidonias niger and White-winged Black Tern C. leucopterus, about 50 of each; Bee-eater Merops apiaster, small groups flying west; Turtle Dove Streptopelia turtur, very large numbers, and Lesser Grey Shrike Lanius minor and Red-backed Shrike L. collurio, very large numbers.

4 June 1960. ANTHONY LAMBERT.

SOME LAND BIRDS NOTED AT SEA BETWEEN MOMBASA AND THE ENGLISH CHANNEL

These notes were made in 1956 while on board the R.M.V. ' Durban Castle ', between Beira and the English Channel. I am indebted to the Extra Second Officer for details of the ship's position when migrants were sighted. Other passengers helped in report- ing birds to me, and Mr. D. Goodwin gave me help and advice at the British Museum (Natural History) in checking the identification of a few species with which I was unfamiliar.

27 April. 1 May.

No migration was seen between Mombasa and the Gulf of Aden. At 9.20 (12" 36' N., 46" 20' E.) in the Gulf of Aden, about 70 miles from

Arabia, a Collared Turtle Dove Streptopelia decaocta arrived from the port side; another or the same seen later at 15.00. At 12.30 about 25 miles from Arabia, a European Nightjar Caprimulgus aropaeus flew round the stern. We arrived at Aden 13.30.