16,4 McGregor: Some Features of the Philippine Ornis 395 
and so all of the members of the band are able to secure more 
food than if they moved about singly or in pairs.®® 
The following paragraph is in agreement with this idea : 
In tropical forests, where insects are everywhere abundant, the birds 
seemed to have realized the fact that to each is apportioned certain 
phases of insect life, and that by hunting in large flocks, instead of com- 
petition resulting between birds of different species, they play into each 
other’s hands (or rather beaks). It is of such a flock that Hudson writes: 
“The larger creepers explore the trunks of big trees, others run over the 
branches and cling to the lesser twigs, so that every tree in their route, 
from its roots to the topmost foliage, is thoroughly examined, and every 
spider and caterpillar taken, while the winged insects, driven from their 
lurking-places, are seized where they settle, or caught flying by the tyrant- 
birds.” 
Swynnerton has published an interesting paper on this phase 
of the bird life of southeast Africa in which he gives us many 
of his own observations. He quotes Bates as saying that — 
The simplest explanation appears to be this: that the birds associate 
in flocks from the instinct of self-preservation, and in order to be a less 
easy prey to hawks, snakes, and other enemies than they would be if 
feeding alone. 
Marshall,®’’ in a paper on the birds of Mashonaland, seems to 
agree with Bates. He says: 
A fact which must impress every observer is the way in which one 
may often walk for several miles through likely-looking country and 
scarcely see a bird; then suddenly one comes upon a troop of them, 
composed of Drongos, Tits, small Shrikes, Flycatchers, Warblers, and 
Buntings, keeping more or less together in a limited area. Personally 
I have little doubt that this may be attributed to the large number of 
birds of prey which occur here; so that the smaller birds find it advisable 
to associate as a means of protection, the Drongos acting as a sort of 
body-guard. My view is supported by the fact that the phenomenon is 
observed principally in the open forest which characterizes the greater 
part of the country; while, wherever the bush is more dense and affords 
better cover, the small birds are more generally distributed. 
Swynnerton says that he has seen birds attending a party of 
monkeys that was moving through the tree tops. He concludes 
his paper with the following paragraphs : 
While, however, I feel that the mixed parties are primarily drives, 
and the Drongo from this standpoint mainly parasitic, it is, I think, 
“ It is perhaps worth while recording that I had written the above 
paragraph before I had seen any of the following notes by other authors 
on the same subject. 
“Beebe, C. W., The Bird: its Form and Function. Henry Holt and 
Company, New York (1906) 150. 
Swynnerton, C. F. M., Mixed bird-parties. Ibis X 3 (1915) 346-354. 
The Naturalist on the Amazons 2 (1863) 334-336. 
"Marshall, G. A. K., Ibis VII 4 (1900) 222. 
