298 _ BRITISH BIRDS. 
country and Central Abyssinia C. equatorialis occurs, which is somewhat 
intermediate between it and the Common Swift. In its dimensions it is 
exactly intermediate between these two species, and has the dark belly of 
the latter, but the less forked tail of the former. z 
The Alpine or White-bellied Swift very closely resembles the Common 
Swift in its habits. It is, however, much more of a rock bird, and is 
rarely seen except amongst mountains. It delights to frequent the bare 
heights, the stupendous passes and ravines, the perpendicular cliffs and 
rocks, where, secure from all enemies, it can rear its young in peace. It 
is generally a gregarious bird, and is usually met with in large or small 
flocks. Like its congener it is a somewhat late summer visitor to Europe, 
seldom arriving in Spain and Asia Minor before the last half of March, 
and in Switzerland not before May, generally leaving again in August. 
In Palestine Canon Tristram says that-it arrives much earlier than the 
Common Swift. The first time he noticed them was on the 12th of 
February, when at Jerusalem he saw large flocks, apparently on migration, 
flying north at a great height and with amazing rapidity. It is pro- 
bably a partial resident in the valley of the Jordan, which may be regarded 
as an outlying island or a peninsula of the Ethiopian Region which 
stretches northwards far into the Palearctic Region. The zoological 
regions are bounded longitudinally by seas which are geographical boun- 
daries, but their extent to the north or south is simply a question of 
climate. The valley of the Jordan enjoys a tropical climate because it lies 
below the level of the sea, and it consequently belongs to the Ethiopian 
Region. 
As might naturally be expected from a bird which, small as it is, 
measures nearly two feet in expanse of wing, the Alpine Swift is capable 
of very rapid and powerful flight. It sometimes flies near the ground, 
especially in the morning and evening and in rainy weather, but at other 
times it searches for its insect food in the highest air, occasionally going 
beyond the range of human vision. 
The Alpine Swift is rarely seen on the ground and scarcely attempts 
to walk, its long wings and short legs causing its mode of progression 
to be little better than shuffling or creeping; but if alarmed it has not 
the slightest difficulty in instantly taking wing. The structure of its 
feet makes it difficult for it to perch on a branch or horizontal surface, 
but against the perpendicular face of a cliff or tower it clings with the 
greatest ease. The hole in which the nest is built serves as a roosting- 
place for both birds, and, after the young are hatched, for the whole family. 
Like its British ally it is an early riser, and is often seen abroad before 
dawn. It dashes in reckless haste along the face of the rocks, or darts 
down like a feathered meteor to the plains ; then ascends far up into the 
sky, wheeling in large circles, gliding smoothly along, turning suddenly 
