The land and fresh-water avifauna of Micronesia consists of 147 kinds of
birds. Of these, 37 kinds are non-residents, 104 kinds are residents,
and 6 kinds have been introduced by man. The 104 resident birds include
98 kinds (94 percent) which are found only within the confines of
Micronesia. Included in these 98 kinds which are restricted to
Micronesia are 5 endemic genera, 31 endemic species and 76 endemic
subspecies.
Gulick (1932: 407, 413) stresses that the fauna and flora of the oceanic
islands may be "disharmonic" (he uses Easter Island as his example) and
says, "It is evident that mature groups of islands will attain an
internal harmony, from the standpoint of the systematist. But this
harmony, instead of reflecting the pre-existing harmony of some
continental source (as in the case of the continental islands or
land-bridge remnants) will be recognizably derivable by descent from a
quite limited number of original importations, at the start distinctly
miscellaneous and 'disharmonic'." Analysis of the land and fresh-water
avifauna of Micronesia supports Gulick's view.
[Illustration: FIG. 7. Divisions of the islands of part of the Pacific
Basin from the standpoint of the distribution of land birds and
fresh-water birds: (1) Micronesia; (2) Hawaii; (3) Central Polynesia;
(4) Eastern Polynesia; (5) Southern Melanesia; (6) Melanesia.]
As mentioned previously, the islands of Micronesia, from the
zoogeographical viewpoint, have been regarded as a part of the
Polynesian Subregion of the Australian Region. Mayr (1941a: 192) defines
the Polynesian Subregion as comprising "all the tropical and subtropical
islands of the Pacific Basin which indicate by their impoverished fauna
that they have had no recent continental connection (after early
Tertiary) and which derived the major part of their fauna directly or
indirectly from the Papuan Region or jointly from Australia and the
Papuan Region." As based on the distribution of the resident avifauna,
Mayr (1941a:193) subdivides the Polynesian Subregion into the following
districts: Micronesia ("including Palau, the Marianne, Caroline,
Marshall, and Gilbert islands"); Central Polynesia ("including Fiji,
Tonga, Samoa, Phoenix, Ellice, Union islands, and a number of small
islands, such as Rotuma, Fotuna, Keppel, Niue, Niouafu, and Uvea");
Eastern Polynesia ("all the islands east of 165° W"); and Southern
Melanesia ("including the Santa Cruz group, Banks Islands, New Hebrides,
Loyalty Islands, and New Caledonia"). He considers that the Hawaiian
Islands, Solomon Islands, and possibly New Caledonia are bordering
districts to the Polynesian Subregion. Figure 7 shows the divisions of
the islands of the Pacific Basin from the standpoint of the distribution
of the land and fresh-water birds. I have placed the Gilbert and
Marshall islands in the Central Polynesian rather than in the
Micronesian District. For purposes of discussion in this report,
however, I am considering the Marshalls to be a part of Micronesia. The
birdlife of the Bonin and Volcano islands northward of the Marianas is
regarded as having its closest affinities to the Japanese avifauna. The
Papuan or Melanesian Subregion of the Australian Region includes the
districts of New Guinea and Northern Melanesia, including the Bismarck
Archipelago, the Admiralty Islands, and the Solomon Islands.
The resident land and fresh-water birds of Micronesia have been derived
from several sources. Studies of these birds and their closest relatives
in adjacent areas indicate that the avifauna has been derived from five
different sources: Polynesia, Melanesia, the Moluccas and Celebes,
Philippines, and Palearctica.