Birds of Micronesia which have been derived directly from Palearctica are Gallinula chloropus guami, Otus podarginus, Asio flammeus, Acrocephalus luscinia and Anas oustaleti. Apparently Gallinula, Asio, and Acrocephalus arrived in Micronesia by way of the chain of islands from Japan southward to the Bonins, Volcanoes, and Marianas. Otus reached Palau from Asia, possibly by way of the Philippines. The smallness of the representation of this component may result partly from lesser ability of the northern birds to adapt themselves to, and to establish themselves on, the semi-tropical and tropical islands of Micronesia as compared with birds from Melanesia where the climate and ecologic conditions resemble more closely those found in Micronesia. Evidence supporting this possibility is the large number of Palearctic residents in the Bonin and Volcano islands as compared with fewer in the Marianas; the Bonins and Volcanoes are less tropical and more temperate in climate.

Table 11 lists the birds concerned, by faunal areas from which the birds have been derived and shows the number of kinds of birds which are present as a result of these colonizations. There is some overlap in the numbers since some endemics may be found in more than one area in Micronesia. [Figure 8] shows the faunal areas from which the endemic land and fresh-water birds of Micronesia have been derived. Melanesia (Papua) supplied 52 percent of this population. Birds reaching Micronesia by way of the Moluccas and Celebes include 21 percent of the total population. The Philippines have supplied 10 percent; Polynesia, 9 percent; and Palearctica, 8 percent. This population of endemic land birds and fresh-water birds has seemingly evolved from 46 colonizations, of which 27 have been derived from Melanesia, 6 from the Philippines, 5 from the Moluccan and Celebean areas, 5 from Palearctica, and 3 from Polynesia.

The Palaus have received a large part of their avifauna from the west (Moluccas, Philippines, Palearctica). Their Melanesian component is mostly the result of secondary colonization from the Carolines. The Carolines have received a greater share of their land birds and fresh-water birds from Melanesia and a smaller share from Polynesia. The Marshalls are definitely associated with the Polynesian element. The Marianas exhibit a considerable amount of secondary colonization from other Micronesian islands, as well as some unique components from the Philippines, Melanesia, and Palearctica. Thus, the number of endemics in Micronesia provides little information concerning the actual number of successful colonizations by birds from other areas. Many of the endemics probably have resulted in this way: Individuals of an endemic subspecies flew to another island and there underwent further differentiation, producing another endemic subspecies. Such secondary colonization probably is going on now.

This analysis of the avifauna shows that Micronesia, with the exception of the Marshall Islands (and the Gilbert Islands), has but little affinity to Polynesia. It has greater affinity, from the zoogeographical standpoint, with the Papuan Region (Melanesia).

Table 11. Avifaunal Components Which Make Up the Endemic Resident Land and Fresh-water Bird Population of Micronesia

Table 11. Avifaunal Components Which Make Up the Endemic Resident Land and Fresh-water Bird Population of Micronesia

Faunal ComponentPalauWestern
and central
Carolines		Eastern
Carolines		MarianasMarshalls
Polynesian2 3 5 0 3
Melanesian11 14 16 12 0
Moluccan-Celebean6 3 4 7 0
Philippine6 2 2 4 1
Palearctic2 1 2 5 0
Totals27 23 29 28 4

Speciation

Of the 104 native fresh-water birds and land birds which are resident in Micronesia, only 7 kinds or 6.5 percent remain undifferentiated from populations elsewhere. These birds are Phalacrocorax melanoleucus, Pandion haliaetus, Demigretta sacra, Ixobrychus sinensis, Anas poecilorhyncha, and possibly Lonchura punctulata (may be an introduction by man). Another bird, Gallinula chloropus, a resident at Palau, may or may not be distinct from the gallinule of Malaysia, G. c. orientalis. Of the 104 resident birds, 97 kinds or 93.5 percent have become differentiated and can be separated taxonomically from populations elsewhere. Of the kinds of birds which are found only in Micronesia, there are 5 endemic genera (16 percent), 31 endemic species (32 percent) and 76 endemic subspecies (75 percent). If we consider the avifauna of Micronesia as a single element, the endemism is high as compared with that on larger and less isolated islands. For example, Mayr (1944a:174) found 137 resident birds on Timor including 22 endemic species (16 percent) and 67 endemic subspecies (47.5 percent). Stresemann (1939b:313) found 220 species including 84 endemic species (38.2 percent) on Celebes. Mayr (1944a:174) also writes that on Java, of 337 breeding species, 16 (4.8 percent) are endemic, and on New Caledonia, of 68 species 19 (27.9 percent) are endemic. Speciation in Micronesia has not progressed much farther than that at New Caledonia and not so far as at Celebes, but subspeciation has progressed considerably more than at the island of Timor. The avifauna of the Hawaiian Islands, as recorded by Bryan and Greenway (1944), has 73 resident land birds and fresh-water birds, all of which are endemic, including one family, 23 genera and 36 species. The North American night heron, Nycticorax n. hoactli, may be included in this list as the only resident which is undifferentiated. The development of full specific differentiation within the resident avifauna is greater in the more isolated Hawaiian chain where 49 percent of these birds are regarded as endemic species, while in Micronesia, which is less remote from other bodies of land, the specific endemism is only 32 percent.

Table 12. Endemism in Families of Native Land and Fresh-water Birds in Micronesia