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

Geographic range.—Micronesia: Mariana Islands—Guam, Rota, Tinian, Saipan.

Characters.—Adult: Resembles closely A. o. angus in the amount of greenish gloss present on the body feathers, but with slightly shorter and deeper bill.

Immature: Resembles the immature of A. o. angus but streaks on underparts brighter and less-dingy yellow.

Measurements.—Measurements are listed in table 45. The writer (1948:69) has given average measurements for the length of wing of adult males from Guam as 127, from Rota as 122, from Tinian as 131, and from Saipan as 131; for depth of bill of adult males from Guam as 9.0, from Rota as 9.0, from Tinian as 9.5, and from Saipan as 10.0.

Weights.—The NAMRU2 party obtained weights of six adult males from Guam as 84-96 (87); of eight adult females from Guam as 78-108 (86); of two juvenal males from Guam as 88 and 90; of five juvenal females from Guam as 77-87 (80); of two adult males from Rota as 70 and 83; and of five juvenal males from Rota as 64-80 (76).

Specimens examined.—Total number, 95 (55 males, 37 females, 3 unsexed), as follows: Mariana Islands, USNM—Guam, 44 (Jan. 21, 22, Feb. 5, March 8, 13, April 12, May 18, 22, 24, 27, 29, 30, June 3, 4, 6, 14, 16, 18, July 6, 7, 14, 20, Aug. 24, Oct. 8, Nov. 19, 23)—Rota, 12 (Oct. 18, 19, 26, 27, Nov. 2)—Tinian, 4 (Oct. 12, 18); AMNH—Guam, 16 (Jan. 23, 24, 29, March 3, 12, 13, 24, May, Aug. 12, Nov. 23, 28, Dec. 26)—Tinian, 15 (Sept. 7, 8, 10, 11, 12)—Saipan, 4 (July 9, 17, Aug. 26, Sept. 2).

Nesting.—The NAMRU2 party found evidence of nesting by starlings at Guam as early as January 28, in 1945. On this date a bird was seen to carry food into a hollow tree at Oca Point. Signs of nesting activities were observed in the months that followed, the last record being obtained on June 11. Starlings nest in cavities in trees, in holes in rocky cliffs, and probably in the tops of coconut palms. On June 2 a nest was found by Muennink in a cavity of a banyan tree at Oca Point, Guam. The nest was approximately 12 feet from the ground and consisted of a flattened mass of green foliage at the bottom of the cavity. Two eggs found in the nest have been described by the author (1948:69) as "Niagara green" with scattered, irregular spots of color, near "russet," "Mars brown" and "pallid purple-drab," most abundant near the large ends. Measurements are 32.1 by 22.1 and 32.0 by 22.4.

Yamashina (1932a:394) records two eggs taken at Saipan on April 14, 1931; two eggs taken at Rota on March 10, 1931; and one egg taken at Rota on March 11, 1931. Seale (1901:54) writes that the starling nests in a hole in the dead trunk of the coconut palm and may lay three or four eggs. Hartert (1898:59) reports that two eggs were taken at Guam on March 11.

Food habits.—Probably the chief food of the starling at Guam is the fruit and seeds of the papaya. This plant grows in most parts of the island, especially in the lowlands where land uses have disturbed the climax vegetation. Many of the garden plots lay fallow during the war and were allowed to grow up in thick stands of papaya. As a fruit began to ripen, the starlings would peck out one side of a ripe fruit, feeding on the tissues and the seeds. It was seldom that a fully ripe papaya fruit was found that had not been at least partly eaten by the starlings. Apparently the birds do not feed on the fruit before it is fully ripened. Seeds of other types of vegetation were also eaten by the birds.

Parasites.—Wharton (1946:174) records the chigger (Acarina), Trombicula sp., from the starling at Guam.

Remarks.—According to Oustalet (1895:212), the starling was taken in the Marianas by the expedition in the "Uranie" in 1820 and by the expedition in the "Astrolabe" in 1829. Kittlitz, who visited Guam from March 1-20, 1828, also recorded the starling. It was not until 1922, however, that the starling in the Marianas was recognized as subspecifically distinct from the birds in the Carolines and Palaus. The Japanese ornithologists named the bird at Guam as A. o. guami and the bird at Saipan as A. o. harterti, but later regarded these as a single subspecies A. o. guami. Momiyama (1920:2) had, previously to the naming of the new forms in the Marianas, considered the bird at Saipan as belonging to the same subspecies as that found at Yap. Among named kinds, A. o. guami found at Guam, Rota, Tinian, and Saipan appears to be most closely related to A. o. angus. These two subspecies differ in that the streaking of the underparts in the immatures is brighter in A. o. guami and duller in A. o. angus. The bird at Saipan has a longer wing and a deeper bill than the bird at Guam; however, birds at Tinian show intermediate measurements.

At Guam, the starling is the most numerous land bird. The writer (1947b:124), in counting birds along the roadways of Guam, recorded the starling on all of the 125 counts and found the birds to include more than one-half (57.3 percent) of all the birds seen. Starlings may have increased during the years of the war, with the disruption of normal agricultural activities allowing the growth of papaya and other food plants in fallow areas; however, the use of the birds as food by the islanders probably increased during the war.

As at other islands in Micronesia, the numbers of birds in immature plumage at Guam seemingly exceeds the number of birds in adult plumage. Animals which may prey on the starling at Guam include the feral house cat, Rattus mindanensis, Corvus kubaryi, and the large lizard Varanus indicus. The starling spends little time on the ground; it feeds principally in the trees, which might limit the amount of damage done to it by the feral house cats which are numerous on the island. The rat, R. mindanensis, is a semi-arboreal animal and may feed on eggs and young birds in nest cavities of trees or on cliffs. The crow, C. kubaryi, has a reputation for stealing chicken eggs from poultry yards and may prey on the eggs and young of the starling. The monitor lizard, V. indicus, is known to prey on the starling, as well as on the domestic chickens at farm houses. On January 31, 1945, one of these large lizards was seen descending a tree after robbing a nest of a starling; one of the starling's eggs was seen in the mouth of the lizard. The noise and commotion set up by the parent birds and by other starlings, which had been attracted to the area, did not appear to perturb the uninvited guest.

Downs (1946:103) writes that the starling at Tinian is less common than the white-eye, Zosterops conspicillata saypani. Gleize (1945:220) estimated the population of starlings on Tinian at 200. Coultas (field notes) found the starling abundant at Tinian in 1931, but he did not find the bird at Saipan. According to Stott (1947:527), the starling was abundant at Guam but "appeared to be common only locally on Saipan." He saw large flocks at the Marpi Point and Kingman Point areas on Saipan but found the bird less numerous elsewhere on the island. At Rota, the NAMRU2 party found the birds to be numerous and widely distributed over the island in 1945.

At Guam, the present writer observed behavior of the starling on January 31, 1945, which may have been a courtship ceremony. Two adults were perched on a palm frond approximately 20 feet above the ground. The bird which was perched more distally on the frond opened its tail fan-fashion, spread its wings and at irregular intervals picked up in its beak a part of the frond and then released it. As this behavior was taking place, the birds would call in a sweet ascending song, which reminded me very much of the song of the redwing blackbird of North America. This was indeed a contrast to the usual squawking notes of this subspecies.

Aplonis opacus aeneus   (Takatsukasa and Yamashina)

Micronesian Starling

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

Geographic range.—Micronesia: Caroline Islands—Ponapé.

Characters.—Adult: A small, dark starling with upper parts sooty-brown, darker on head with forehead and lores blackish; wings, rump, upper tail-coverts, and tail lighter and more brownish than head; underparts paler and washed with olive-brown; bill and feet black; iris brown.

Immature: Resembles adult, but lighter brown, especially the underparts.

A. pelzelni differs from A. opacus by having no gloss on the feathers, smaller size, more slender bill, and a brown iris.

Measurements.—Measurements are listed in table 46.

Specimens examined.—Total number, 59 (32 males, 24 females, 3 unsexed), from Caroline Islands, AMNH—Ponapé (Dec).

Nesting.—Coultas (field notes) obtained reports that the Ponapé Mountain Starling nests in cavities in trees and lays two eggs.

Table 46. Measurements of Aplonis pelzelni