Aplonis opacus aeneus Mayr, Birds Southwest Pacific, 1945, p. 297 (Agrigan, Pagan, Almagan); Borror, Auk, 64, 1947, p. 417 (Agrihan).
Geographic range.—Micronesia: Mariana Islands—Alamagan, Pagan, Agrihan, Asuncion.
Characters.—Adult: According to Takatsukasa and Yamashina (1931:487), A. o. aeneus resembles A. o. orii of Palau, but has a bronze rather than green luster. A. o. aeneus resembles A. o. opacus, but has a smaller bill.
Remarks.—No specimens of this subspecies have been examined by me. Little information is available regarding the occurrence of this subspecies in the northern Marianas. Oustalet (1895:212) writes that Marche collected four specimens at Pagan and three at Agrihan. Borror (1947:417) writes that in 1945, it was a "common and abundant species" at Agrihan. He obtained one specimen between July 27 and August 14 and comments that it had a grasshopper in its stomach.
Evolutionary history of Aplonis opacus.—Aplonis opacus is known from the Mariana, Palau, and Caroline islands in Micronesia. It consists of several subspecies, which have relatively few distinguishing characteristics. No starlings are known in the Marshall and Gilbert islands, although atolls occur in these island-chains that offer a habitat approximately the same as those in the western Carolines now occupied by A. o. angus.
In regard to parental stock, Sharpe (1876:47) considered A. opacus as "nothing but a slightly more metallic race of C. mysolensis, with a still stouter bill." The species with which Sharpe compared A. opacus is known from Mysol, Buru, and Ceram. Oustalet (1896:70) thought that the Aplonis in Micronesia belonged to a group of starlings whose members are scattered through the Pacific islands including Cook, Samoa, Tonga, Fiji, New Britain, New Guinea, Banta, Mysol, Salwatti, and Timor. Mayr (1941b:204) is of the opinion that Aplonis in Micronesia was derived from central Polynesia. Amadon (1943:8), in his study of the genera of starlings, places A. opacus within a superspecies containing A. cinerascens, A. tabuensis, A. fuscus, and possibly A. feadensis and A. cantoroides. All of these are blackish birds with greenish gloss with immatures having the underparts streaked. In comparing A. opacus with these mentioned species and with other species of Aplonis, I find that A. opacus more closely resembles A. feadensis and A. cantoroides than any others. Although there are differences in size of the bill, wing, and tail, these structures are proportionally the same. The streaked underparts of the immatures of A. cantoroides are much like that of the immatures of A. opacus, whereas the immatures of A. feadensis are only faintly streaked with whitish below. The eye of A. cantoroides is red, and that of A. opacus is more nearly yellow. The ancestral stock from which A. opacus developed in Micronesia seemingly reached the area from Melanesia. In Micronesia the birds dispersed to various groups of islands from some point in the Caroline Islands. The birds are absent from the Marshall Islands. Perhaps the birds never reached the Marshall Islands or they may have been present in former times and disappeared since then.
Aplonis pelzelni Finsch
Ponapé Mountain Starling
Aplonis pelzelni Finsch, Proc. Zool. Soc. London, 1875 (1876), p. 644. (Type locality, Ponapé.)