396 | Philippine Journal of Science 1920 
likely that the great “mobbing”? power afforded by numbers must be so 
great an advantage as to probably act as a contributing factor. I think, 
too, that the Drongo, with his boldness and readiness to attack, quite 
likely fully “pays for his keep.” 
The fact of systematic co-operative hunting on so large a scale suggests 
the views on mutual aid amongst animals that have been laid stress on 
by some Russian naturalists; yet is of particular interest as suggesting 
how keen selection must sometimes be and how baseless, probably, is the 
view that the more perfect defensive adaptions of insects constitute 
hypertely. 
At another time a family of four or five fiery minivets (Pert- 
crocotus) comes into sight. The adult male is brillant red or 
orange and black, the female and young are yellow and black. 
The minivets are rare and seem to care little for the company 
of other birds. The various species of forest orioles (Oriolus) 
and of fairy bluebirds (Irena) move about in pairs; they feed 
among the branches of the tallest trees, and their presence is 
usually revealed by their characteristic call notes some time 
before they can be seen. 
Few of these forest-inhabiting species are even seen in the 
open. As Worcester ** remarks, birds in the Tropics “may be 
born, grow old, and die within the limits of a single grove, and 
never suffer want of food or shelter.” This seems to account for 
the fact that many species of birds are confined to single islands, 
in some cases to very small islands. The species having been 
developed in a thick forest, the individuals never leave it and have 
no chance or inclination to extend their range to other islands, 
however near. Furthermore, in the forest they are perfectly 
protected from being driven to sea or to other islands by winds, 
no matter how powerful. 
There are many endemic species that are seldom found except 
when they are feeding at flowering or fruiting trees. Days oF 
even weeks may be spent without an individual of these species 
being seen; but when a favorite tree is found in flower or fruit 
it is only necessary to wait nearby, where as many specimens 
as desired can be collected. 
The species of Dicwum, Prionochilus, Leptocoma, Cyrtosto- 
mus, Athopyga, Iole, and Loriculus, especially, can be obtained 
in quantities at trees in flower. One tree that is a particular 
favorite with many species of birds is the dap-dap, Erythrina 
indica, which has large scarlet flowers from January to April; 
as it usually casts most of its leaves during anthesis the flowers 
are rendered very conspicuous. Zimmer * gives a good picture 
* Proc. U. S. Nat. Mus, 20 (1898) 581. 
” Philip. Journ. Sci. § D 13 (1918) 350. 
