MIGRATION OF BIRDS IN AFRICA 



545 



All of these birds cited as examples are 

 common and conspicuous, easily observed, 

 and could not have passed unnoticed had 

 they been resident throughout the year. 

 The white -bellied stork, white-necked bee 

 eater, red-winged buzzard, and pennant- 

 winged nightjar offer four clear-cut examples 

 of migration within the tropics Some of the 

 species, however, which we found to be 

 migratory in the Uele, are distributed over all 

 the more open parts of Africa, and to judge 

 from the dates at which they have been 

 taken in various regions do not migrate 

 north and south in this way. 



The common yellow-billed kite {Milvus 

 cegyptiiis) is a perplexing case. In the forest 

 belt it is never common; the carrion insects, 

 and other weak prey on which it feeds are 

 not easy for it to find; but a stray indi- 

 vidual may be seen in almost any month. 

 On rare occasions large flocks are seen passing 

 over. In the Ituri we have noticed them 

 going southward in August. In the savannah 

 districts just north and south of the forest belt 

 they are very abundant in the dry season, but 

 practically absent in the rainy months. As 

 these seasons alternate to the north and south, 

 we might jump to the conclusion that the kites 

 simply migrate across the forest like the 

 pennant-winged nightjar. Such does not 

 appear to be the case, however, for in many 

 parts farther removed from the equator, 

 both north and south, they are found through- 

 out the year. Moreover, at the very limits 

 of their range, they are present only in the 

 summer (rainy season). At the same period 

 then, when they increase in numbers just 

 north of the forest, they are likewise invading 

 South Africa in flocks, and conversely, at 

 the season when they gather about grass 

 fires just south of the forest they are also 

 increasing in numbers in Senegal and visiting 

 the islands of the eastern Mediterranean. 

 Their movements thus seem to be correlated 

 from north to south, but no large body of 

 kites migrates from South to North Africa, 

 and they nest everywhere save in the equa- 

 torial forest. 



The cattle heron {Bubulcus ibis) is another 

 bird of wide distribution, from southern 

 Europe and central Asia to South Africa 

 and Madagascar. But the cattle herons of 

 the northeastern Congo act like northern 

 migrants, arriving in late October and Novem- 

 ber, when, according to plumage and other 

 indications, they have finished nesting. 



Toward January they are rare, as though 

 they had continued farther south, but by 

 April they are again numerous, and vanish 

 regularly before the middle of May, after 

 some of them have assumed the buff plumes 

 of the nuptial dress. 



Bates also writes that they are seen in 

 the Kamerun in November and in May. 

 These Inrds must breed in Africa, farther 

 north; but others of the species are known to 

 breed in the south, where they are not con- 

 sidered migratory. 



This is a case like those which caused 

 Dixon to suspect a neutral zone of "winter- 

 ing" or non breeding birds in central Africa. 

 But in some instances at least, as the quail and 

 bittern, the South African birds have been 

 found to be distinct from the European, 

 subspecifically at least. As far as I have 

 seen, there is no such neutral zone in the 

 Congo. If such a zone did exist, in the case 

 of the cattle heron, it would have to be south 

 of the equator, but the cattle herons of 

 South Africa are not known to migrate 

 at all. 



Migration, then, although less charac- 

 teristic of birds in the tropics, does take 

 place not only among birds of temperate 

 South Africa, but also even among many that 

 nest within ten degrees of the equator. 

 These movements are regular, like those of , 

 more northern birds, and are probably due 

 to variation in the food supply, governed of 

 course by seasonal changes — • here rains and 

 drought rather than heat and cold. In the 

 case of the pennant-winged nightjar, the 

 migration may insure a bountiful diet of 

 winged termites (a favorite food of this and 

 many other birds), since these insects fly in 

 the greatest numbers toward the beginning 

 of the rainy season. But whatever its 

 causes, we have still a great deal to learn of 

 the simple facts of bird migration on the 

 great African continent. 



Seasonal journeys, even in the north- 

 eastern Congo, are by no means restricted to 

 birds. In the Ituri District several species 

 of butterflies are seen traveling northward 

 in enormous numbers at definite seasons, 

 and the common yellow-necked fruit bat 

 {Eidolon helvum) seems to have some similar 

 habit. In the northeastern Uele even the 

 elephants go northward into the savannah 

 during the rainy months, and retire again to 

 the border of the forest on the approach of 

 the dry season. 



