MIGRATION OF BIRDS. 393 removal from one place to another, it may be asserted that the greater part of the animals of Africa are forced to make such changes. The difference in the commencement of the rainy season throughout the grassy or wooded uplands, both north and south of the equator, naturally influences the ripening of fruits and the development of insect life, upon which the higher classes of animals depend for subsistence. Hence arises the necessity for the latter to leave tracts which are beginning to get dry, and to go in search of others which yield the necessary means of subsistence in greater abundance. A good example of this wandering caused by the necessity of finding food is afforded in the Chrysospizza lutea, Licht., which frequents the steppe in flocks at the first commencement of the summer .

rain, and builds its nests in the acacia brushwood, but, as soon as the steppe becomes withered and dry, collects in small companies and removes to the banks of the larger rivers and brooks, visiting even towns and villages. ‘These birds may thus be seen in the winter months by hundreds in Khartum, together with Passer domesticus, L. The same is true of some weaverbirds. It is, then, quite natural that, when the steppe yields no more food, its feathered inhabitants should retire, in part at least, to the south, where an abundant feast awaits them. I mention as a well-known example Hyphantica ethiopica, Sund., which in summer frequents the tablelands of Kordofan, Sennar, and Takale, but in the wimter chooses for its abode the region between Sobat and the 4th parallel of N. lat., because the beds of rushes in this tract supply suitable dwellings and food. But besides the need of food, which causes birds as well as all other animals to change their residence, it must be remembered that limited districts, which are able in ordinary times to harbour a certain number of birds, become too small for them, particularly in the breeding season, because, on the one hand, each pair demands a larger space, and on the other, the consumption, of insects especially, is considerably increased. Hence results a movement which in our territory is chiefly from south to north, though migrations to the south are not unknown.

It would be superfluous to give examples of this movement - from south to north; all that have hitherto been called African