DR. EMIL HOLUB. 197 
to rest, and soon they are asleep. But do not think, dear 
reader, that with the retirement of the Swallows every sign 
of life has ceased in the dark marsh for the night. Though 
the night has set in, we soon hear peculiar low tones coming 
from the thicket of reeds. We hear the melancholy song 
of the Sylvias, the voices of the Night Herons and of the 
Bitterns, and from time to time the gurgling cry of the 
sentinel among the gray Cranes mingles with them, generally 
followed up by the cries of the whole troop of Cranes. 
Another Crane takes the watch until his cry again puts these 
large birds on the alert against the sly attacks of hyenas and 
jackals. 
The day is dawning. The song of the gray Sylvias and 
the Bittern’s loud boom are soon drowned in the noise of the 
hundreds of thousands of Swallows which have just awak- 
ened, and in the loud cries of the large birds, which try at 
first a walk on the moist bank of the swamp, before they 
leave for the plains. Our friends, the Swallows, rise after a 
good deal of squabbling about the dreams of the night past ; 
they leave in small swarms—as I think, those coming from 
certain European districts keeping together for the whole 
time of their African sojourn—and make at once for the 
different portions of that endless plain, on which they are 
accustomed to hunt dayafter day. But they do not rise high 
up in the air to fly in any particular direction; taking the 
proper course at first, they commence at once to search for 
food, reaching their proper hunting-field—may it be near or 
very far off—by thus flying low along the high grass, and 
taking with their breakfast the glittering drops of the morn- 
ing dew to quench their thirst. 
Who could count the millions of insects the swarms of 
Swallows which rest at this one marsh destroy in a single 
day on that South African plain? Count now all the sleep- 
ing-places; count now all the swarms of this most useful 
bird ; consider also the number of days of our winter, dur- 
ing which the Swallows remain in the far south; and if 
