Anas poecilorhyncha superciliosa Delacour and Mayr, Wilson Bull., 57, 1945, pp. 21, 39 (no locality given); Yamashina, Pacific Science, 2, 1948, p. 122 (Palau, Truk).
Geographic range.—Islands of Micronesia, Polynesia, and Melanesia. In Micronesia: Palau Islands—Babelthuap, Peleliu; Caroline Islands—Truk.
Characters.—Adult: A medium-sized duck with upper parts dark brown, feathers edged with buff; top of head blackish merging into gray on hind neck with narrow buff line below; eye-stripe broad and blackish; lower parts uniformly dark brown to gray brown, feathers edged with buff; face, chin and throat light buff with some dark streakings; under wing white; speculum green; bill plumbeous with nail black; legs yellow-brown to yellowish, webs dusky. A. p. pelewensis resembles A. p. rogersi Mathews, but is smaller with a wing length averaging as much as 20 mm. shorter.
Measurements.—As given by Amadon (1943:4) seven unsexed skins from the Palaus, studied by Finsch (1875:40), have wing lengths of 207, 212, 212, 214, 223, 235, 230. For an adult male taken by Coultas at Palau, the exposed culmen measures 45 and the tarsus 37.
Specimens examined.—Total number, 3 males from Palau Islands, AMNH—exact locality not given (Oct. 26, Nov. 25).
Remarks.—A. p. pelewensis is apparently rare in the Palau Islands. Coultas, who visited the Palaus in October to December, 1931, writes (field notes) that he received reports that the birds were present and nested in numbers on fresh water lakes. He took specimens in taro patches and comments that the ducks probably feed at night and have retiring habits during the day. At Peleliu in 1945, the NAMRU2 party received several reports of ducks but failed to find the birds. At Truk, in December, 1945, McElroy of the NAMRU2 party found ducks to be fairly numerous in rice paddies, marshes, and swamps. He observed that the birds roosted at Moen Island at night but that they apparently flew to outlying islands to spend the day. Richards observed ducks on Moen Island on August 28 and 29, 1947, and again in the period from January 19 to February 10, 1948. He saw several flocks of ducks including one containing "about a dozen ducks" at ponds along a roadway and at an airstrip. Kuroda named the population at Truk as distinct in 1939. I have not been able to examine his description and no specimens are available for study, but if the birds at Truk represent an independent colonization (different from that of the birds at Palau) they might exhibit recognizable variation. Amadon (1943:5) has already pointed out that the shortness of the wing of specimens in the Palaus may merit subspecific status for the population. Delacour and Mayr (1945:21) propose that the Palau Gray Duck is a subspecies of A. poecilorhyncha; this treatment is followed in the present work.
Evolutionary history.—A. p. pelewensis, as Amadon (1943:1) has stated, represents a population of mallards which became separated from the ancestral stock in the Australian or Malayan area and when once differentiated, invaded New Zealand and other parts of Polynesia, Melanesia, and southwestern Micronesia. Amadon points out that its range in the Pacific islands is more or less complimentary to that of A. oustaleti in the Marianas and the Philippine Mallard (A. poecilorhyncha luzonica Fraser), as well as to the Hawaiian forms (A. wyvilliana Sclater and A. laysanensis Rothschild). The range of A. p. pelewensis gives one the impression that its present distribution may be only a stage in a gradual spreading of the species, for it certainly has not yet occupied all habitats suitable for it in southern Micronesia nor elsewhere in Oceania. As in the case of A. oustaleti, A. p. pelewensis appears to prefer areas of fresh, and possibly brackish, water on the larger islands.
A. p. luzonica is a near relative of A. p. pelewensis but has rufous-brown instead of buffy-brown coloring on the chin, throat, sides of head, and superciliary region. The underparts of the Philippine Mallard are much less mottled. The specula are similar. Both of these forms were probably derived from a mallard of the A. p. poecilorhyncha type.