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

Family	Residents	Endemic genera	Endemic species	Endemic subspecies	Total endemic
Phalacrocoracidae	1	0	0	0	0
Ardeidae	3	0	0	1	1
Anatidae	2	0	1	0	1
Accipitridae	1	0	0	0	0
Megapodidae	2	0	1	2	2
Rallidae	7	1^*	2	4	6
Columbidae	13	0	4	11	13
Psittacidae	1	0	1	0	1
Strigidae	1	0	1	1	2
Caprimulgidae	1	0	0	1	1
Apodidae	5	0	1	5	5
Alcedinidae	7	0	1	7	7
Apodidae	3	0	0	3	3
Corvidae	1	0	1	0	1
Sylviidae	5	1	2	4	5
Muscicapidae	14	1	6	9	14
Artamidae	1	0	0	1	1
Sturnidae	9	0	3^[+]	7	9
Meliphagidae	7	1	1	6	7
Zosteropidae	14	1	6	10	14
Ploceidae	5	0	0	4	4
Totals	104	5	31	76	97

^* Aphanolimonasa is included but may be extinct.

^[+] Aplonis corvinus is included but may be extinct.

[Table 12] lists the families of land birds and fresh-water birds which have resident members as part of the avifauna of Micronesia. It can be observed from the table that only two families are represented by no endemic kinds, several families are represented by one or two endemic kinds, and others are represented by as many as 14 endemic kinds. Endemism has reached its greatest development in the families Rallidae (6), Columbidae (13), Apodidae (5), Alcedinidae (7), Sylviidae (5), Muscicapidae (14), Sturnidae (9), Meliphagidae (7), and Zosteropidae (14). Generic endemism is greatest in the Sylviidae where one endemic genus occurs among 5 endemic species and subspecies (20 percent), in Rallidae one in 6 (17 percent), in Meliphagidae one in 7 (14 percent). Specific endemism is greatest in Psittacidae and Corvidae where the single representative of each family in Micronesia is considered specifically distinct (100 percent), in Megapodidae and Strigidae one in 2 (50 percent), in Muscicapidae and Zosteropidae 6 in 14 (43 percent) in Sylviidae 2 in 5 (40 percent), in Rallidae 2 in 6 (33 percent), in Sturnidae 3 in 9 (33 percent) in Columbidae 4 in 13 (31 percent). Subspeciation within species which are endemic in Micronesia has occurred in 8 families, occurring within two species in each of the families Columbidae and Zosteropidae and once in each of the families Megapodidae, Apodidae, Alcedinidae, Sylviidae, Muscicapidae, and Sturnidae.

In summary, the families of land and fresh-water birds found in Micronesia which have the greatest number of endemic forms are Muscicapidae (14), Zosteropidae (14), Columbidae (13), and Sturnidae (9). Speciation has occurred in the single representative of the families Psittacidae (Trichoglossus rubiginosus) and Corvidae (Corvus kubaryi). Where family representation is large, speciation has occurred most frequently, as in the Muscicapidae (6 in 14 = 43 percent), in the Zosteropidae (6 in 14 = 43 percent), and in the Columbidae (4 in 13 = 31 percent). Subspeciation has occurred in 8 families, in two species in the Columbidae and Zosteropidae and in one species in each of 6 other families.