162 
NATURAL HISTORY 
for many weeks together, both spring and fall : during 
which periods myriads of the swallow kind traverse the 
Straits from north to south, and from south to north, 
according to the season. And these vast migrations con- 
sist not only of Hirundines , but of bee-birds, hoopoes, 
Oropendolas/ or golden thrushes, &c., &c., and also of many 
of our soft-billed summer birds of passage ; and, moreover, of 
birds which never leave us, such as all the various sorts 
of hawks and kites. Old Belon, 200 years ago, gives a 
curious account of the incredible armies of hawks and kites 
which he saw in the spring-time traversing the Thracian 
Bosphorus from Asia to Europe. Besides the above-men- 
tioned, he remarks that the procession isk swelled by whole 
troops of eagles and vultures. 
Now, it is no wonder that birds residing in Africa should 
retreat before the sun as it advances, and retire to milder 
regions, and especially birds of prey, whose blood being 
heated with hot animal food, are more impatient of a sultry 
climate ; but then I cannot help wondering why kites and 
hawks, and such hardy birds as are known to defy all the 
severity of England, and even of Sweden and all north 
Europe, should want to migrate from the south of Europe, 
and be dissatisfied with the winters of Andalusia.^ 
It does not appear to me that much stress may be laid 
on the difficulty and hazard that birds must run in their 
* Oropendola is the Spanish name for the Golden Oriole. — Ed. 
2 The migration of the kites and hawks no doubt depends in a 
measure upon that of the smaller birds upon which they prey ; in the 
same way that some of the latter are influenced by the appearance or 
disappearance of locusts and other insects, which form their chief food. 
In Lloyd's " Game Birds and Wild-fowl of Norway and Sweden," 
p. 370, there is a wonderful picture by "Wolf, entitled " The Bird- 
cloud," in which, in illustration of the author's remarks, the artist has 
depicted a vast flock of wild fowl on migration harassed by birds of 
prey. In Andersson's " Birds of Damaraland," p. 264, a singular 
account is given of the way in which the pratincoles (^Glareola melan- 
optera) attend the flying swarms of locusts in South Africa. The. 
writer says : — " These birds come, I may say, in millions, attendant on 
the flying swarms of locusts ; indeed, the appearance of a few of them 
is looked upon as a sure presage of the locust swarms being at 
hand. ' --Ed. 
