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336 GEOGRAPHICAL ZOOLOGY. [part it-
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. If 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 tl^at 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 Nicobar-pigeon of Malaya, and the black and
crimson Aledrcenas 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
New 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 Dididte.
The curious liking of pigeons for an insular habitat is well
shown in the genera lanthcenas and Calcenas. The former, con-
taining 11 species, ranges over a hundred degrees of longitude,
axid forty-five of latitude, extending into three regions, yet
nowhere inhabits a continent or even a large island. It is
;