None of the above workers, however, obtained very much information on comparative numbers of species.
Tables8,9, and10present the writer's findings on populations of migratory shore birds in Micronesia in 1945. At Guam, as shown intable 8, the records for March, April and early May are few, owing to a limited amount of field observation. Beginning in late May and until October 24 a greater amount of time was spent in the field and more regular records were obtained. No observations were made by the author at Guam in the period from August 11 to September 25. The dates marked with an asterisk are those on which observations were made on the extensive tidal flats at Agfayan Bay and vicinity. These flats, at low tide, present excellent feeding grounds for waders and in 1945 were undisturbed by parties of service personnel, because the area was "off-limits."
Table 8shows thatPluvialis dominica,Numenius phaeopus, andHeteroscelusspp. were the shore birds most frequently found at Guam in this period.Pluvialis dominicawas the most numerous of the three species. OfHeteroscelusthere was approximately equal representation ofH. incanusandH. brevipesas indicated by specimens collected. These birds were not identified to species in the field.
Although records were made only infrequently in the spring migration, such information as was obtained indicates that the populations were largest in March and early April. On April 24,Pluvialis dominicawas the only bird observed on beaches and in upland openings. On April 26, a singleLimosa lapponicawas recorded. On May 15, no shore bird was seen on a trip along several beaches. In late May and early June, single individuals ofHeterosceluswere found. Of this genus, those collected in May were in nuptial plumage, and those collected in June were in winter plumage and probably should be classed as non-migrants.Numenius phaeopuswas occasionally recorded beginning in early June, but waders were totally absent from beaches at Agfayan Bay and vicinity on June 18 and 19. Few shore birds were seen in early August. In late September, birds, especiallyPluvialis dominica,Numenius phaeopus, andHeteroscelusspp., were numerous. These species were numerous until October 24, when observations were discontinued.
Of the 17 species of migratory shore birds recorded from the Mariana Islands, eight were identified. Of these eight, three species,Limosa lapponica,Actitis hypoleucos, andCharadrius mongolus, were found on only one occasion. Never more than four specieswere identified on a single field trip. These data give an idea of the lack of variety of species that may be observed on Micronesian islands.
Table 9. Populations of Migratory Shore Birds Seen at Ulithi Atoll in 1945
Table 9. Populations of Migratory Shore Birds Seen at Ulithi Atoll in 1945
*Figures based on identified skins.x Observed but numbers not recorded.
*Figures based on identified skins.x Observed but numbers not recorded.
*Figures based on identified skins.
x Observed but numbers not recorded.
Table 9lists the shore birds seen at Ulithi Atoll, Caroline Islands, on eight field excursions in the period from August 14 to August 22, 1945. Of seven species of shore birds known to visit the atoll, six were taken in this period. As observed at Guam,Pluvialis dominicaandNumenius phaeopuswere the species most frequently found.Heterosceluswas seen on three occasions; those collected were identified asH. incanus. Most of the shore birds were seen at Pau and Losiep, islands unoccupied by man. Similar tidal flats are present at most of the other small islands in the atoll, but these islands (Asor, Fallalop, Potangeras, Fassarai and Mangejang were visited) were occupied by small detachments of service personnel or by natives, which may have tended to keep many of the shore birds away. At the more populated islands of Asor and Fallalop, no shore birdswere seen. Almost as many species were recorded at Ulithi on the eight field trips as were found by the author at Guam in eight months of observations.
Table 10. Populations of Migratory Shore Birds Seen at the Palau Islands in 194
Table 10. Populations of Migratory Shore Birds Seen at the Palau Islands in 194
*Observations made on beaches at Akarakoro Point, Peleliu.x Observed but numbers not recorded.[+]Observations made at fresh water ponds.[++]Figures based on identified skins.
*Observations made on beaches at Akarakoro Point, Peleliu.x Observed but numbers not recorded.[+]Observations made at fresh water ponds.[++]Figures based on identified skins.
*Observations made on beaches at Akarakoro Point, Peleliu.
x Observed but numbers not recorded.
[+]Observations made at fresh water ponds.
[++]Figures based on identified skins.
Table 10presents field counts at the Palau Islands in the period from August 24 to September 21, 1945. Of 20 species of shore birds known from the Palaus, 17 species were collected or identified on this trip. It was apparent that the fall migration was at its height at this time. Birds were numerous at inland openings and ponds, air field strips, and on the extensive tidal flats at Akarakoro Point. The latter area is between Peleliu and the adjacent island of Ngesebus to the north. Several observations were made at this area (as indicated by the dates marked with asterisks in the table); on September 8, 271+ shore birds were counted; on September 16,129+ were counted. Six species were observed to be abundant. The majority of the birds found at these beaches were in small flocks which consisted of several birds of one or more species.
The birds observed at Angaur on September 21 were seen at several fresh and brackish ponds. Four species (Tringa glareola,Erolia acuminata,Limicola falcinellus,Gallinago megala), which were not taken on the tidal flats or elsewhere at Peleliu, were found at these ponds.
The abundance, and more especially the variety, of shore birds at the Palau Islands during this period was in marked contrast to the smaller and less diversified populations of shore birds in rather similar insular environments at Ulithi and Guam. These differences offer support for the supposition that the Asiatic-Palauan Migratory Shore Bird Flyway is distinct from the Japanese-Marianan Migratory Shore Bird Flyway.
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 BasinFig. 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 oftheir 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 7shows 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 andNorthern 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.
Aphanolimnas monasa(extinct?),Ptilinopus porphyraceus, andDucula oceanicaare 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, andDuculaapparently invaded Micronesia from Central Polynesiaviathe Marshall Islands through a rather continuous chain of islands and atolls.Aphanolimnasis known only from Kusaie in the extreme eastern part of the Carolines whilePtilinopusandDuculaare known from the Marshalls, Carolines, and Palaus.
The Papuan or Melanesian Region (New Guinea, Bismarck Archipelago, Solomon Islands) has supplied to Micronesia its greatest number of endemic land and fresh-water residents. Fifty kinds of birds belonging to the following species reached Micronesia from Melanesia:Nycticorax caledonicus,Megapodius lapérouse,Ptilinopus roseicapillus,Gallicolumba xanthonura,G. canifrons,Caloenas nicobarica,Halcyon cinnamomina,Trichoglossus rubiginosus,Collocalia inquieta,Edolisoma tenuirostre,Rhipidura rufifrons,Metabolus regensis,Monarcha godeffroyi,M. takatsukasae,Colluricincla tenebrosa,Aplonis opacus,A. pelzelni,A. corvinus(extinct?),Cleptornis marchei,Myzomela cardinalis(probably by way of Southern Melanesia),Rukia palauensis,R. oleaginea,R. ruki,R. sanfordi,Erythrura trichroa. The colonization of Micronesia by these species has probably extended over a considerable period of time.Megapodius,Trichoglossus, andAplonis corvinusmay represent oldercolonizations which have become well differentiated from the ancestral forms;Nycticorax,Myzomela, andErythruramay have become established later and have had "less time" to become modified from the ancestral forms. Birds from Melanesia have reached Micronesia probably by direct flight to the Caroline Islands. Aided by favorable winds which blow from the southwest, south and southeast during the period from May to November, birds, particularly the young of the year, might conceivably be blown in the direction of the Carolines, where 57 percent of the birds derived from Melanesia reside. The Palaus are populated with 15 percent, the Marianas with 28 percent, and the Marshalls (lacking "high" islands) with none; these may be secondary colonizations from the Carolinas exceptingPtilinopus,Megapodius,Gallicolumba canifrons,Cleptornis, andColluricincla. The Marshall Islands have received no avian components from Melanesia. The absence of "high" islands in the Marshalls and the possible inability of birds accustomed to life on the luxuriant islands of Melanesia to become established on relatively barren atolls are logical reasons for this. Instead of New Guinea itself, the outlying islands of Melanesia (Bismarck Archipelago, Solomons, Southern Melanesia) probably have been the principal "taking-off" places for birds invading Micronesia.
Birds which reached Micronesia by way of the islands of Celebes and the Moluccas may have been derived originally from Melanesia. The following birds appear to have used this route:Porphyrio porphyrio, probablyHalcyon chloris,Rhipidura lepida,Myiagra oceanica,Zosterops conspicillata, andZ. cinerea. These birds apparently became established initially in the Palaus;PorphyrioandRhipidura lepidahave not been recorded elsewhere in Micronesia, butMyiagraand the two species ofZosteropshave spread to the Carolines and Marianas, although not into the Marshall Islands. Wind from the southeast in summer and fall has probably been a factor aiding these colonizations. The population ofGallinula chloropusresident at Palau may also have arrived by this route.
Ten of the kinds of birds of Micronesia have come from or by way of the Philippine area. These are known principally from the Palaus and the Marianas and include:Rallus philippinus,R. owstoni,Poliolimnas cinereus,Caprimulgus indicus,Corvus kubaryi,Psamathia annae,Artamus leucorhynchus, possiblyLonchura nigerrima, andCollocalia inexpectata. The Philippines may have been the actual point of dispersal of the birds (example,Psamathia), or may have been used as a stepping stone to Micronesia by birds coming from Melanesia (examples,RallusandArtamus), by birds from Malaysia (example,Collocalia), and by birds from Asia (example,Caprimulgus). Two birds of this component have reached the islands of eastern Micronesia. A subspecies ofLonchura nigerrimais endemic at Ponapé, and a subspecies ofPoliolimnas cinereusoccurs on several islands in the Carolines and has even been recorded at Bikini in the Marshall Islands. Three species are known only from the Palaus; two are known only from the Marianas.
Fig. 8Fig. 8.Faunal areas from which the resident land birds and fresh-water birds of Micronesia have been derived. (1) Palearctica; (2) Philippines; (3) Moluccas and Celebes (Malaysia); (4) Melanesia (New Guinea and northern Melanesia); (5) Polynesia.
Birds of Micronesia which have been derived directly from Palearctica areGallinula chloropus guami,Otus podarginus,Asio flammeus,Acrocephalus lusciniaandAnas oustaleti. ApparentlyGallinula,Asio, andAcrocephalusarrived in Micronesia by way of the chain of islands from Japan southward to the Bonins, Volcanoes, and Marianas.Otusreached 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 birdsto 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 8shows 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), hasbut 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