Notes on the Taxonomy, Natural History, and Status of the Resident Birds of Palau
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THE CONDOR JOURNAL OF THE COOPER ORNITHOLOGICAL SOCIETY Volume 82 Number 2 May 1980 NOTES ON THE TAXONOMY, NATURAL HISTORY, AND STATUS OF THE RESIDENT BIRDS OF PALAU H. DOUGLAS PRATT JOHN ENGBRING PHILLIP L. BRUNER AND DELWYN G. BERRETT ABSTRACT.-This paper reports observations made from 1976 to 1979 of the resident birds of the Palau Islands in western Micronesia. Comments on population status, distribution, and habitat are made for all species. Song descriptions and food habits are reported for many species. Nests are de- scribed for Megapodius laperouse, Ptilinopus pelewensis, Cettia (=Psama- thia) annae, Myiagra erythrops, Rhipidura lepida, Zosterops cinerea, My- zomela cardinalis, Aplonis opaca, and Artamus Zeucorhynchus. Taxonomic comments are made on Ptilinopus, Coracina, Psamathia, Myiagra, Colluri- cincla, and Megazosterops. The recommendation is made that Pyrrhoglaux podargina, Rhipidura lepida, and possibly Megapodius laperouse be declas- sified as Endangered Species, but that Palau populations of Rallina eurizo- noides, Gallinula chloropus, Porphyrio porphyrio, and Caprimulgus indicus be considered for such listing. The Palau Islands lie at the western ex- U.S. Forest Service has begun surveys of treme of Micronesia about equidistant from birdlife in Micronesia, including Palau Mindanao, the Moluccas, and New Guinea (Ralph and Sakai 1979). Because of the (Fig. 1). The islands are part of the U.S. awakening interest in Palauan birds, we Trust Territory of the Pacific Islands have prepared this summary of our recent (TTPI), but that status will change in the observations in order to provide information near future when the trusteeship expires. and show where information is lacking. As Although possessing the richest avifauna in most of our notes on migrants will be Micronesia, Palau has been sadly neglected published elsewhere (Pratt and Bruner, in by ornithologists until recently. Only a few press), this paper deals only with the resi- brief notes on the birds have appeared in dent breeding birds. Our comments on sta- the almost three decades since Marshall tus are preliminary assessments pending (1949) and Baker (1951) published their ob- publication of Engbrings’ quantitative data. servations. In recent years the work of Rob- For the most part, the nests reported herein ert P. Owen (1977a, b, and c), TTPI Chief are the first for the species. Our knowledge Conservationist, at the Trust Territory Bi- of Palauan birds has been greatly increased ology Laboratory at Koror in Palau has be- by conversations with Owen, and we in- gun to focus attention on Palauan birds once clude many of his observations as well as again. A proposal to build an oil tanker some of the information contained in three superport at Palau has made environmen- unpublished government reports (Owen talists aware of the islands (Gosnell 1976) 1977a, Engbring 1977, 1978). and has at last brought some Federal atten- Berrett, Bruner, and Pratt first visited Pa- tion. A survey of bird populations at Palau lau in June 1976 and studied on Koror, Ma- has recently been completed by John lakal, Arakabesan, southern Babelthuap, Engbring under Owens’ direction. Also the Peleliu, and the Seventy Islands Preserve Condor, 82: 117-131 [I171 @ The Cooper Ornithological Society 1980 118 H. D. PRATT ET AL. ._._,‘_.“...; ,..., .I:,.:’ ., ../‘ : f ; ,_/ .. .: z-Z. /i ,. : c.. ’ ,i .: VOLCANO IS. ...‘ .; : ’ ; ,:. :, \ . 3 : ._;“: :...: :.*:.<‘ : :,, ..‘ .%‘ /?‘ _. .,‘ ;. ’ ,.. i... : ’ i‘ .‘ ..‘ <:;,‘ 2.:‘ i PAL AU ““$‘ ’ $,..; i CAROLINE IS. FIGURE 1. The Southwest Pacific showing the lo- cation of Palau and other islands mentioned in the text. (Fig. 2). Pratt returned to Palau 16-23 Jan- uary 1978 and conducted investigations on southern Babelthuap, in additional areas on Peleliu, and to a lesser extent on Koror, Malakal, and Arakabesan. Bruner and Pratt revisited the islands from 24 June to 4 July 1978, observing (with Engbring) additional areas, particularly the central islands south of Koror. Engbring arrived in Palau 1 July 1977 and began fieldwork in September of that year. He visited all areas of Palau dur- ing his service through June 1979. Pratt has recorded numerous bird vocal- izations, the first ever of Palauan birds. These tapes are deposited in the Library of Natural Sounds, Cornell Laboratory of Or- :..p ANGAUR nithology. Our efforts to obtain permits to FIGURE 2. Map of Palau showing the major islands take specimens of birds were unsuccessful. mentioned in the text. Islands of coralline limestone Palau District Code, Section 202, protects (rock islands) are indicated in solid black. Dotted lines (on paper at least) most birds of the islands indicate coral reefs. and makes no provision for scientific col- lecting. This situation is unfortunate in that little anatomical material and no tissue sam- and habitats of Palau is that of Gressitt ples of Palauan birds exist, and many taxo- (1954). In general, the southern islands are nomic questions may require such speci- of raised coral limestone and the northern mens for satisfactory resolution. Efforts are ones are of ancient volcanic soil. Some is- now under way to persuade local legislators lands, such as Koror, have some volcanic to amend their well-intentioned statute so and some coralline areas (Fig. 2). The lime- as to allow collecting under permit (Owen, stone islands between Koror and Peleliu are pers. comm.). largely uninhabitable. They are covered with a dense growth of forest over jagged THE ISLANDS coralline rubble on precipitous slopes. The main Palau Islands (Fig. 2) range in These “rock islands” are characteristically size from Babelthuap (397 sq. km) to tiny undercut at the waterline by water solution rock islets. All except the southernmost is- and the action of marine organisms such as land of Angaur and two outlying atolls to chitons, with only a few sheltered beaches. the north are enclosed within a single reef Peleliu lies on the barrier reef at the south- system. An excellent account of the geology ern end and is a relatively flat coralline is- THE BIRDS OF PALAU 119 TABLE 1. Summary of distribution and status of Palauan land and freshwater birds. Status abbreviations: A, abundant; C, common; U, uncommon; R, rare; X, extirpated; ?, status uncertain. Babelthuap Arakabesan KOXX Urukthapel Eil Malk Peleliu Angaur Ixobrychus sine&s C U U U U U C Anus superciliosa R X R R Megapodius laperouse R R U C C C C Gallus gallus C U U A A Rallina eurizonoides U U U U U U U Rallus philippensis C C C A Poliolimnas cinereus R R R Gallinula chloropus X X R Porphyria porphyrio U R U Caloenas nicobarica R R U U Gallicolumba canifrons R R U U R Ptilinopus pelewensis A A A A A Ducula oceanica A C A A Pyrrhoglaux podargina C C C C R Caprimulgus indicus U U R R Cacatua galerita R R U U Eclectus roratus R R U U Aerodramus vanikorensis C C A Halcyon cinnamomina C U C ?z Halcyon chloris C C C C C C Coracina tenuirostris U U U U Cettia annae A C A Myiagra erythrops C C ; C Rhipidura lepida U C C Colluricincla tenebrosa C C C Zosterops cinerea A C C Zosterops conspicillata C C C U Megazosterops palauensis C A Myzomela cardinalis C C C C C Erythrura trichroa U U U Lonchura malacca A Aplonis opaca A A A A A Artamus leucorhynchus R land with extensive beaches; it supports a THE AVIFAUNA small human population. Angaur, separated from Peleliu by 10.5 km of open ocean, is The Palauan avifauna comprises represen- a low, flat island which also has a small hu- tatives of 38 families, either as breeding res- man population. Both Peleliu and Angaur idents or migrant visitors. A high level of were devastated by World War II (Baker endemism at the species or subspecies level 1946) and their vegetation is entirely sec- characterizes the terrestrial avifauna, but ond growth. Nevertheless, at least on Pele- the breeding seabirds are species that are liu some areas of tropical forest have re- widespread in tropical waters (Baker 1951). covered impressively. The main population The migrants include winter visitors from center of Palau is on the volcanic western the Asiatic mainland and Japan. Shorebirds part of Koror, with satellite communities on predominate among such visitors but the neighboring Arakabesan and Malakal. These list also includes herons, raptors, and pas- three islands are joined by causeways and serines. A few species visit Palau during the are collectively known as the Koror com- southern winter. plex. They are devoted largely to agricul- Several Palauan birds are listed as En- ture and residential areas, but forests re- dangered Species by Federal (Federal Reg- main on the western end of Arakabesan and ister, 26 September 1975) or local (Title 17, on the limestone eastern portion of Koror. Code of the Trust Territory) statutes. The Babelthuaps’ population is mainly confined inclusion of these birds in the Federal list to the coastal periphery of the island, with was apparently based on published ac- very little disturbance of the vast and, prior counts shortly after the cessation of World to Engbrings’ work, ornithologically little War II (Marshall 1949, Baker 1951), when known interior forests. With fewer than avian habitats had been severely disturbed 15,000 people, Palau cannot be said to be by battle (Baker 1946). As we will indicate, overcrowded. several of these species seem to have re- 120 H. D. PRATT ET AL. covered completely and may eventually be herons congregate at times at the garbage removed from the lists (Owen, pers. comm.). dump/landfill site at Koror, particularly at Several others not now listed may warrant high tide. When tides are low, Rufous inclusion, however. Table 1 shows the dis- Night-Herons disperse to mudflats in the tributions among the major islands (Fig.