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aThe numbers in this column are probably underestimates because they include only species that breed in the East Palaearctic and winter entirely in Africa (leaving no other possible wintering area) or the few species in which such a long migration has been confirmed by ringing. Future ringing is likely to reveal that some individuals of other species also migrate from the East Palaearctic to Africa. The figures are based primarily on information given in The Birds of the Western Palaearctic, and are larger than those given by Moreau (1972) mainly because of increased information resulting from ringing data.

aThe numbers in this column are probably underestimates because they include only species that breed in the East Palaearctic and winter entirely in Africa (leaving no other possible wintering area) or the few species in which such a long migration has been confirmed by ringing. Future ringing is likely to reveal that some individuals of other species also migrate from the East Palaearctic to Africa. The figures are based primarily on information given in The Birds of the Western Palaearctic, and are larger than those given by Moreau (1972) mainly because of increased information resulting from ringing data.

Only about 25 species come from the eastern Palaearctic, beyond 90°E, and some even from across the Bering Sea in Alaska and the Yukon. Some of these birds on their journeys travel as much as 200° west, covering more than 9000 km by the shortest (great circle) route, and then cross the equator and even the tropic of Capricorn. They include such spectacular travellers as the Amur Falcon Falco amurensis, Northern Wheatear Oenanthe oenanthe and Willow Warbler Phylloscopus trochilis.

Many Eurasian species winter partly in Africa and partly in southern Asia. It is assumed that each of these species has a migratory divide, with populations on the west side wintering in Africa. However, only for relatively few of the species is the pos-ition of the divide known, and from how far east the migrants to Africa derive, but in some the divide is surprisingly far to the east. For example, recoveries of Barn Swallows Hirundo rustica ringed in Africa have come from a wide range of localities from Ireland in the west to Siberia at more than 95°E (Turner 2006). Hence, Barn Swallows from most of the breeding range converge on southern Africa for the northern winter. Similarly, an Imperial Eagle Aquila heliaca was radio-tagged and tracked by satellite from western Saudi Arabia to a potential breeding area in northern China beyond 85°E (Meyburg & Meyburg 1998). Again, one would have expected such a bird to have wintered in India, along with others of its kind.

In total, an estimated 5000 million landbirds leave their Palaearctic breeding grounds each year to winter in Africa south of the Sahara, a density equivalent to one migrant per 1 ha of breeding range (Moreau 1972). To these must be added millions of shorebirds and waterfowl,1 and also seabirds which winter offshore. More recent estimates, made 40 years later and based on radar observations across the Mediterranean region, lay between 3500 million and 4500 million birds

(B. Bruderer, in litt.), but these figures would have excluded migrants from east of Europe that enter Africa across Arabia. Radar has also revealed that, although some migration occurs across the whole width of the Mediterranean and Sahara, densities are highest at the western and eastern ends, where sea-crossings are short or avoided (Bruderer & Leichti 1999). Owing to human activities on breeding areas, Moreau (1972) felt that prevailing migrant numbers were only about one-third of those present at their maximum in post-glacial times, perhaps 3000 years ago. The migrants compare in numbers to an estimated 70 000-75 000 million other birds that live in Africa year-round (Brown et al. 1982). In other words, despite their impressive numbers, the migrants form only about 6-7% of the total bird numbers in Africa during the northern winter. However, their relative proportions vary greatly from one region to another and from one type of habitat to another, reaching their highest densities in the northern savannas (see later).

The fact that so many species from the mid-Palaearctic make the long westerly flight to Africa, rather than southwards within Asia, is presumably due partly to the conditions prevailing in southern Asia. The area of land west of 70°E with a genial winter is limited (India and Pakistan cover only 4 million km2 compared with 21 million km2 in Africa south of the Sahara), and between 75° and 95°E lies the formidable mountain mass of Tibet, flanked on the south by the even higher Himalayas. The Tibetan plateau averages nearly 5 km above sea level, covers 2.5 million km2, and spans 2000 km from north to south, while the Himalayan peaks rise to over 8 km and span another 200 km from north to south. Nevertheless, birds of about 27 species and subspecies breeding in the mid-Palaearctic do winter in India, mostly 'leaking round the two ends of the Tibetan massif' (Moreau 1972). Many other birds cross the Tibetan Highlands and the Himalayas in autumn when conditions are favourable, but avoid this region in spring when most is still snow-covered and frozen (Bolshakov 2001). Moreover, India attracts for the winter several species from the west Palaearctic that do not go to Africa, including the Scarlet Rosefinch Carpodacus erythrinus and Arctic Warbler Phylloscopus borealis. From the east Palaearctic, nearly all the migrants move south-southeast into southern Asia, from Burma eastward to Indonesia, on journeys far less strenuous than those undertaken by birds entering tropical Africa from whatever source.

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