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The Avifauna of Micronesia, Its Origin, Evolution, and Distribution

ROLLIN H. BAKER

University of Kansas Publications Museum of Natural History

Volume 3, No. 1, pp. 1-359, 16 figures in text June 12, 1951

University of Kansas LAWRENCE 1951

The Avifauna of Micronesia, Its Origin, Evolution, and Distribution

ROLLIN H. BAKER

University of Kansas Publications Museum of Natural History

Volume 3, No. 1, pp. 1-359, 16 figures in text June 12, 1951

University of Kansas LAWRENCE 1951

UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, A. Byron Leonard, Edward H. Taylor, Robert W. Wilson

UNIVERSITY OF KANSAS Lawrence, Kansas

PRINTED BY FERD VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1951

The Avifauna of Micronesia, Its Origin, Evolution, and Distribution

ROLLIN H. BAKER

PAGE

INTRODUCTION 5

DESCRIPTION OF MICRONESIA 5 Climate 8 Soils 9 Surface water 9 Vegetation 10

GAZETTEER OF THE ISLANDS OF MICRONESIA 11 Mariana Islands 11 Palau Islands 13 Caroline Islands 14 Marshall Islands 15

ORNITHOLOGICAL EXPLORATION IN MICRONESIA 16

CHECK-LIST OF THE BIRDS OF MICRONESIA 21

DISCUSSION OF THE AVIFAUNA 28 Oceanic Birds 28 Inshore Oceanic Birds 29 Offshore and Pelagic Oceanic Birds 30 Faunal Components 30 Migratory Shore Birds 32 Original Homes of the Shore Birds that Visit Micronesia 32 Routes of Migration 34 Populations of Shore Birds in Micronesia 37 Land and Fresh-Water Birds 42 Polynesian Component 44 Melanesian Component 44 Moluccan and Celebesian Components 45 Philippine Component 45 Palearctic Component 46 Speciation 48 Time of Colonization 50 Factors Causing Dispersal 52 Analysis of Speciation 55

CONSERVATION OF THE AVIFAUNA OF MICRONESIA 58

THE FUTURE OF ORNITHOLOGICAL RESEARCH IN MICRONESIA 60

METHODS AND ACKNOWLEDGMENTS 60

ACCOUNTS OF THE KINDS OF BIRDS IN MICRONESIA 63

SUMMARY AND CONCLUSIONS 340

BIBLIOGRAPHY 343

FIGURES IN TEXT

FIGURE PAGE

INTRODUCTION

DESCRIPTION OF MICRONESIA

The vast expanse of the Pacific Ocean is dotted with numerous islands, most of which are concentrated in the central and western part and are known collectively as Oceania. Within Oceania three divisions are popularly recognized: Melanesia, Polynesia, and Micronesia. According to Krieger , the Micronesia islands include the Mariana, Palau, Caroline, Marshall, and Gilbert islands; they may take in also the Volcano, Bonin, and Ellice islands . Zoogeographically, according to Wallace , Micronesia is to be included in the Polynesian Subregion of the Australian Region. Mayr , on the basis of the distribution of birds, ranks Micronesia as one of the four subdivisions of the Polynesian Subregion, and includes within Micronesia the Palau, Caroline, Mariana, Marshall, and Gilbert islands. Except in the discussion of distribution, this report does not treat of the avifauna of the Gilbert Islands, which straddle the equator south of the Marshall Islands. This report is concerned only with the birds in the Mariana, Palau, Caroline, and Marshall islands formerly mandated to Japan, and with the birds of the island of Guam, which is a possession of the United States.

Geologists and oceanographers have shown , that islands of Micronesia are of two general types: arcuate and strewn. The Pacific Ocean is surrounded by rising mountain ranges which are arranged in elongated, near-circular arcs, which form an extended series of scallops. In the western Pacific these sweeping arcs extend into the ocean, where the mountain ranges project upward from the bottom of the sea with only the crests showing above the waves to point out, in dotted outline, the position of the mountains. The easternmost of these arcs is marked by the islands of the Aleutians, Kuriles, Japan, Izo, Bonins, Volcanoes, Marianas, Yap, Palaus, and others continuing southward into Melanesia. These are characterized by igneous rocks of andesitic nature.

To the eastward of the arcuate islands in Micronesia, are numerous and irregularly distributed islands, making up all of the central and eastern Carolines and the Marshalls, which are known as strewn islands. Strewn islands mark the places of former volcanoes or volcanic peaks. If these volcanic peaks have been completely drowned and are now marked by a series of low islands edged by a protecting reef formed by coral growth enclosing a lagoon and with all exposures consisting of coral rock, the island is known as a coral atoll . Some of the coral exposures lack lagoons; they are known merely as coral islands . Some atolls become elevated by geologic activity and the lagoons may dry out or drain. The accumulation of guano of oceanic birds and the residue of fish and other organisms in the area of the lagoon remains as a rich phosphate deposit; these raised atolls have been called phosphate islands . Other strewn islands consist of igneous rocks which are exposed above the surface of the ocean. These are known as "high" or volcanic islands and may occur as a single mountain rising out of the ocean , or be partly drowned and surrounded by a coral reef . The igneous rocks found on these strewn islands are basaltic in nature.

The Mariana Islands consist of a chain of volcanic islands approximately 450 miles long. As shown in figure 2, there are 14 single islands and one group of three islands , from Uracas in the north to Guam in the south. The Palau Islands which are situated in the easternmost part of Micronesia have often been considered from a political standpoint as part of the Caroline Islands. As shown in figure 3, the Palau Islands are a chain of islands approximately 120 miles long from north to south. Sonsorol, Tobi, Merir, Pulo Anna, and Helen Island occur to the southward of the Palaus and may be considered as part of the Carolines or as part of the Palaus. The Palaus together with the Carolines, to the eastward, extend in an east-west direction for approximately 1,700 miles. The Palaus and Carolines include 37 atolls, 34 banks, 11 coral islands without lagoons, 2 uplifted phosphate islands, 4 volcanic islands, and the Palau chain. The Marshall Islands to the extreme eastward extend approximately 700 miles from north to south and, as shown in figure 5, contain 29 atolls and five coral islands without lagoons. No volcanic exposures occur in the Marshall Islands.

There is a total land surface of approximately 846 square miles in the islands of Micronesia. The Palaus and Carolines have 525 square miles, the Marianas 247 square miles, and the Marshalls 74 square miles of land surface. Guam has the largest land surface of any of the islands of Micronesia with 225 square miles, Ponap? has 145 square miles, and Babelthuap has 143 square miles. Asuncion, in the northern Marianas, has the highest elevation, rising as an almost perfect cone to a height of 2,923 feet; Ponap? reaches a height of 2,579 feet above the sea level. The volcanic islands are known as "high" islands, and the coral atolls are known as "low" islands. The coral islands usually rise but a few feet above sea level.

CLIMATE

In Micronesia there are two seasons: a wet summer and a dryer winter. Temperatures rarely go above 90? F. and rarely below 70? F. Rainfall in the Marianas averages approximately 85 inches per year, in the Palaus approximately 150 inches, in the Carolines it ranges from 129 to 185 inches, and in the Marshalls it goes up to 160 inches. The humidity is excessive, the average annual mean of relative humidity for selected islands in Micronesia being between 82 and 86 percent. The relative humidity is lower in the western Carolines and the Palaus, than in other parts of Micronesia.

The Mariana Islands lie between the area of the Asiatic monsoon and the belt of the northeast trade winds. At Saipan from November until March or April, winds usually are easterly or northeasterly and are strong and steady since the northeast trades and the winter monsoon reinforce each other. In April and May the directions of the winds shift toward the southeast, and they become weaker and more variable. In this period there may be some easterly winds in addition to the predominating southeasterly winds. Detailed information is not available on the winds which occur in the Marianas north of Saipan, but at Pagan easterly winds probably prevail from May to July and westerly winds prevail in the remainder of the year. The Carolines lie in the belt of alternating northeast trade winds and southwest monsoons. The northeast trades begin in October and prevail until May or June. The southwest monsoon occurs from May to October and may be felt as far east as Truk. To the eastward, the winds of the summer are usually light and variable. In the Marshall Islands, the northeast trade winds predominate from about December to April, especially in the northern part of the Marshalls. In summer, winds are variable and weak; periods of calm may occur. Typhoons and squalls occur most frequently in the spring and summer in Micronesia. Some of the severe typhoons are known to engulf entire islands, as did the one at Woleai in 1907.

SOILS

The soils of the islands of Micronesia have been derived from volcanic materials or from depositions of coralline limestone. Volcanic soils occur on the "high" islands of Micronesia. In many places, especially on the islands of the northern Marianas there is little soil; there are large areas of bare igneous rock, because the islands are geologically of relatively recent origin and little erosion has occurred. On islands where volcanic rocks have decomposed, the resulting soil may have a top layer of humus. The richest soils of the islands are along drainage areas and in alluvial deposits.

Coralline soils result from the decomposition of limestone, coral fragments, shells, and sand, and are overlain by some humus. Where the layer of humus is deep, the fertility is greatest. Coralline-volcanic soils occur on some "high" islands where coral rock and volcanic rock have become mixed in the decomposition process which forms soil. In parts of the Marianas and elsewhere, unwise practices of burning and overgrazing have allowed extensive erosion to occur, resulting in reduced fertility of the soil. On the island of Yap certain sedimentary rocks are exposed which are thought to have been elevated from the ocean bottom. Soils at Yap which have developed from this rock are considered more fertile than soils of coralline origin, although the fertility there also is dependent on the depth of the layer of humus.

SURFACE WATER

There is little fresh water on the coral atolls, but brackish marshes are present on some islands, and many of these marshes are used for the cultivation of taro by the natives. Some volcanic islands, on the other hand, possess small streams and fresh water lakes, producing suitable habitat for certain rails, gallinules and ducks. On the "low" islands in the Marshalls, natural surface pools are rare.

VEGETATION

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