Read Ebook: The Avifauna of Micronesia Its Origin Evolution and Distribution by Baker Rollin H Rollin Harold

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individuals the birds inhabiting the inshore zones are relatively more numerous than those preferring the offshore and pelagic zones, although 12 of the 18 resident kinds of oceanic birds apparently prefer the offshore zone, while only 6 kinds appear to be restricted primarily to the inshore areas.

FAUNAL COMPONENTS

The oceanic birds were probably among the earliest birds to reach the islands of Micronesia. The presence of phosphate deposits on islands , denoting deposition of guano by oceanic birds , indicates long time residence by these birds. A person is prone to think that these deposits must have been made by larger concentrations of oceanic birds than are found in these islands today. Whether there were actually more individuals present during the period of deposition of phosphate in the lagoons of these islands is not known, although the elevation of the lagoons with the resulting freshening of the water probably was a great attraction to oceanic birds, especially to those which prefer to drink fresh water. According to Leonard P. Schultz , the abundance of fish in the areas about these Pacific islands has been approximately the same since Pleistocene times, so that there was apparently no greater concentration of fish near these islands to attract large populations of fish-eating sea birds. Probably the time element is of sufficient magnitude to account for such deposition by birds with a population similar to that found there today.

The oceanic avifauna of Micronesia contains birds which are apparently from ancestral homes in the Palearctic Region, in the North and Central Pacific, in Polynesia, in Melanesia and Malaysia, and from homes the positions of which are uncertain because of the widespread circumtropical occurrence of the birds. There are no sea birds that are endemic in Micronesia.

MIGRATORY SHORE BIRDS

Twenty-eight species of shore birds of the families Charadriidae and Scolopacidae have been recorded from Micronesia, and one other of the family Phalaropodidae apparently occurs in the area, making a total of 29 kinds. From the entire Southwest Pacific, Mayr lists 31 species and subspecies of shore birds and mentions six other species which may occur there. Thus, of a possible 37 kinds of shore birds in this large area , 29 are present in the islands of Micronesia. For purposes of discussion, shore birds are here placed in one of two groups: regular visitors or uncommon visitors. A regular visitor is one which has been recorded in the literature or in unpublished field accounts as being frequently observed in Micronesia in periods of migration. An uncommon visitor is one which has been infrequently observed in Micronesia. Of the 28 kinds of shore birds recorded from Micronesia, 17 are classed as regular visitors and 11 are classed as uncommon visitors.

ORIGINAL HOMES OF THE SHORE BIRDS THAT VISIT MICRONESIA

TABLE 3. BREEDING AND WINTERING GROUNDS OF THE SPECIES OF MIGRATORY SHORE BIRDS IN MICRONESIA

Denotes birds which breed on both American and Asiatic sides of the Pacific Ocean.

The shore birds which are known to visit Micronesia breed in the Northern Hemisphere. Table 3 summarizes the data concerning the breeding and wintering areas of these birds. As shown in part A of table 3, 18 of the 28 species which visit Micronesia come from Asiatic breeding grounds. Seven have circumpolar breeding ranges and three come from American breeding grounds. As shown in part B of table 3, 21 of the 28 waders have their winter ranges on the Asiatic side of the Pacific with eastern extensions to Micronesia and other parts of Oceania. Of the 7 remaining species, the winter ranges of three are circumtropical; the winter range of a fourth is restricted to Oceania; and the winter ranges of the remaining three are American.

The ability of the shore birds to migrate almost as well over water as over land may explain their spread into Oceania. The likelihood that shore birds, when migrating may have ventured to Micronesia and Polynesia initially from the Asiatic side of the Pacific is strongly suggested by the data given in the paragraph above. Also, on the Asiatic side of the Pacific there are large numbers of islands, which form several archipelagoes extending from Kamchatka south to Malaysia. Once accustomed to migrating along these chains of islands from the Arctic to Australia, birds would probably have to make only minor adjustments to extend the breadth of their migratory routes eastward into the islands of the Pacific Ocean. In contrast, on the Pacific coast of North America there are few coastal or offshore islands and there is a vast area of open water separating the Hawaiian Islands from the American mainland. Probably the vastness of this area of water offers little stimulus to birds to expand their migratory ranges westward, and in part accounts for the small North American contingent in the population of shore birds of the Central Pacific. Some North American shore birds do visit the Pacific. The brisk trade winds from the northeast might be an aid to the birds in their flights from Nearctica to Hawaii.

ROUTES OF MIGRATION

The small and isolated islands of Oceania might, upon first inspection, seem to offer but little attraction to shore birds. Hesse, Allee and Schmidt point out that the "open southeastern Pacific" being least supplied with water from land sources, which is an important means of fertility, is known to have one of the poorest faunas found anywhere in the oceans. However, there are extensive tidal flats, especially on the leeward sides of the islands, and these flats apparently afford extensive feeding grounds for these birds. Also, the absence of competition from resident birds as well as the virtual absence of predatory animals are other factors which may help to make the islands attractive wintering grounds for shore birds.

Only a few birds have been banded in the Pacific, and the knowledge which comes from the recovery of banded birds gives but little aid to the student of movements of birds in the Pacific. The probable flyways for migratory shore birds there have to be deduced from sight records, data from specimens collected, known stations of breeding and wintering , and from a study of maps of the region. Analysis of information from the above-mentioned sources indicates that there are three routes taken by shore birds which migrate from Micronesia to and from their northern breeding grounds : Asiatic-Palauan Flyway; Japanese-Marianan Flyway; Nearctic-Hawaiian Flyway.

The information available indicates that migrant shore birds which utilize this flyway move east into the Carolines ; however, the recording of 20 species from the Palaus as compared with only 12 species in the western Carolines indicates that this spread eastward may not be very pronounced. Migrants in autumn probably move from the Palaus in a southerly direction toward the New Guinea area. Eight species of shore birds which reach the Palaus , are not recorded from other parts of Micronesia. Species which apparently utilize the Asiatic-Palauan Flyway are listed in table 5.

Flyways additional to the three suggested above may be utilized by some shore birds on their southward migrations. Species reaching Wake and the Marcus Islands may fly directly south from the islands of the North Pacific. Bryan lists four species of shore birds from Marcus .

TABLE 4. LIST OF SPECIES OF SHORE BIRDS KNOWN FROM FIVE GEOGRAPHICAL AREAS OF MICRONESIA

Western Central Eastern Palaus Carolines Marianas Carolines Carolines Marshalls

Number of species 20 12 17 11 10 10

TABLE 5. SHORE BIRDS WHICH MAY USE THE ASIATIC-PALAUAN FLYWAY

Regular Visitors Uncommon? Visitors

TABLE 6. SHORE BIRDS WHICH MAY USE THE JAPANESE-MARIANAN FLYWAY

Regular Visitors Uncommon? Visitors

TABLE 7. SHORE BIRDS WHICH MAY USE THE NEARCTIC-HAWAIIAN FLYWAY

Regular Visitors Uncommon? Visitors

POPULATIONS OF SHORE BIRDS IN MICRONESIA

Although shore birds have been observed in Micronesia on many occasions, actual counts of numbers of individuals of the different birds have rarely been made. Kubary, Finsch, Marche, Seale and other early collectors and observers record some data of this kind as have the Japanese investigators in later times. William Coultas of the Whitney South Sea Expedition obtained considerable information of this nature at Guam, Saipan, Kusiae, Ponap?, and the Palaus, but it is unpublished. His records were made in fall, winter and spring, when migrants were present in large numbers and these observations offer evidence that many of the migrants are comparatively numerous, especially in the Carolines, throughout the winter months. McElroy's observations made on his trip for NAMRU2 to Truk in December, 1945, offer further evidence of this.

TABLE 8. POPULATIONS OF MIGRATORY SHORE BIRDS SEEN AT GUAM IN 1945

Column headings:

x Observed but numbers not recorded.

Figures based on identified skins.

None of the above workers, however, obtained very much information on comparative numbers of species.

Tables 8, 9, and 10 present the writer's findings on populations of migratory shore birds in Micronesia in 1945. At Guam, as shown in table 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 9. POPULATIONS OF MIGRATORY SHORE BIRDS SEEN AT ULITHI ATOLL IN 1945

Column headings:

Fas.: Fassari Man.: Mangejang Los.: Losiep

x Observed but numbers not recorded.

TABLE 10. POPULATIONS OF MIGRATORY SHORE BIRDS SEEN AT THE PALAU ISLANDS IN 1945

Observations made at fresh water ponds.

x Observed but numbers not recorded.

Figures based on identified skins.

Table 10 presents 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 ; 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 , 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.

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 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 stresses that the fauna and flora of the oceanic islands may be "disharmonic" 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 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.

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 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 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 subdivides the Polynesian Subregion into the following districts: Micronesia ; Central Polynesia ; Eastern Polynesia ; and Southern Melanesia . 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

MELANESIAN COMPONENT

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