Land and Fresh-water Birds
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.
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.
Polynesian Component
Aphanolimnas monasa (extinct?), Ptilinopus porphyraceus, and Ducula oceanica are the only species of birds which have reached Micronesia directly from Polynesia. There are in Micronesia, as Mayr (1941b: 204) points out, eight species "which are members of typically Polynesian species or genera" and six species which are either Papuan or Polynesian. The relationships between Polynesian and Micronesian birds is evident, but insofar as the pathways of colonization are concerned the majority of these Micronesian species listed by Mayr have come from elsewhere than Polynesia and the birds of these two areas are thought to have arisen from common ancestors. Aphanolimnas, Ptilinopus, and Ducula apparently invaded Micronesia from Central Polynesia via the Marshall Islands through a rather continuous chain of islands and atolls. Aphanolimnas is known only from Kusaie in the extreme eastern part of the Carolines while Ptilinopus and Ducula are known from the Marshalls, Carolines, and Palaus.