336 
GEOGRAPHICAL ZOOLOGY. 
[part IV. 
a physical cause for this peculiarity of distribution. Pigeons 
build rude, open nests, and their young remain helpless for a 
considerable period. They are thus exposed to the attacks of 
such arboreal quadrupeds or other animals as feed on eggs or 
young birds. Monkeys are very destructive in this respect; 
and it is a noteworthy fact that over the whole Australian re- 
gion, the Mascarene Islands and the Antilles, monkeys are un- 
known. In the Indo-Malay sub-region, where monkeys are 
generally plentiful, the greatest variety of pigeons occurs in the 
Philippines, where there is but a single species in one island ; 
and in Java, where monkeys are far less numerous than in Sumatra 
or Borneo. It we add to this consideration the fact, that mam- 
malia and rapacious birds are, as a rule, far less abundant in 
islands than on continents ; and that the extreme development 
of pigeon-life is reached in the Papuan group of islands, in which 
mammalia (except a few marsupials, bats, and pigs) are wholly 
absent, we see further reason to adopt this view. It is also to 
be noted that in America, comparatively few pigeons are found 
in the rich forests (comparable to those of the Australian insular 
region in which they abound), but are mostly confined to the 
open campos, the high Andes, and the western coast districts, 
from which the monkey-tribe are wholly absent. 
This view is further supported by the great development of 
colour that is found in the pigeons of these insular regions, cul- 
minating in the golden-yellow fruit-dove of the Fiji Islands, the 
metallic green Mcobar-pigeon of Malaya, and the black and 
crimson Alectroenas of Mauritius. Here also, alone, we meet 
with crested pigeons, rendering the possessors more conspicuous ; 
such as the Lopholaimus of Australia and the crowned Goura of 
Hew Guinea ; and here too are more peculiar forms of terrestrial 
pigeons than elsewhere, though none have completely lost the 
power of flight but the now extinct Hididae. 
The curious liking of pigeons for an insular habitat is well 
shown in the genera Ianthcenas and Calcenas. The former, con- 
taining 11 species, ranges over a hundred degrees of longitude, 
and forty-five of latitude, extending into three regions, yet 
nowhere inhabits a continent or even a large island. It is 
