Proceedings of the United States National Museum
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A REVIEW OF THE BIRDS OF THE ISLANDS OF SIBERUT AND SIPORA, MENTAWI GROUP ^ (SPOLIA MENTA- WIENSIA) By J. H. Riley Assista7it Curator, Division of Birds, United States National Museum Off the west coast of Sumatra lies a long chain of islands of vary- ing size, stretching from Simalur in the north to Engano in the south, a distance of over 700 miles. Dr. W. L. Abbott became inter- ested in this chain and in the autumn of 1901 visited Simalur, Pulo Babi, Pulo Lasia, and the Banjak Islands, making collections on each of them. The bird material of this collection was worked up by Dr. Charles W. Richmond, who published an account of it.- In the autumn of 1902, Doctor Abbott, accompanied by Mr. C. Boden Kloss, revisited Simalur, and then went to the Pagi and Batu Islands, and Nias, the latter already known ornithologically from Modigliani's explorations; in the autumn of 1904 he visited Engano, and early in 1905 returned to Nias. Dr. H. C. Oberholser^ has published an account of the second Abbott collection from Simalur, but the col- lections from the other islands never have been reported upon as a whole, though Oberholser has described many new forms from them, in one paper* no less than 97, with scattered descriptions at subse- quent dates. In this early paper the descriptions are very brief and are unaccompanied by measurements or information concerning the number of specimens upon which his conclusions were based. For this reason it is utterly impossible for any subsequent worker to reach any definite conclusions with material from adjacent islands without consulting topotypical material. ^ The present paper is one of a series under the general heading of " Spolia Menta- wiensia," dealing with collections in natural history made in 1924 in the Mentawi Islands by Mr C. Boden Kloss and his assistants of the RaflBes Museum in Singapore. The National Museum is indebted to the friendly cooperation of Dr. W. L. Abbott for a share In the material secured during this worlt. » Proc. U. S. Nat. Mus., vol. 26, 1903, pp. 485-524. 3 Idem, vol. -55, 1919, pp. 473-498. * Smiths. Misc. Coll., vol. 60, no. 7, 1912, pp. 1-22. No. 2775.— Proceedings U. S. National Museum, Vol. 75, Art. 4 22482—29 1 1 2 PROCEEDINGS OF THE NATIONAL MUSEUM vol.75 At the time Doctor Abbott was active in this region, he was unable to get permission from the Dutch authorities to visit Siberut and Sipora, two islands of fair size lying north of the Pagi Islands, and with them constituting the Mentawi Group. When, in the autumn of 1924, Mr. Kloss and a party from the Raffles Museum, Singapore, visited Siberut and Sipora to make a general natural history survey, Doctor Abbott contributed funds in , aid of the enterprise, in return for which support the United States i National Museum was to receive a set of the duplicates. After writing an account of the birds, in conjunction with Mr. F. N. Chasen,^ Mr. Kloss, the Director of the Raffles Museuni, for- warded the whole collection to Washington, with the exception of ' certain specimens which he took to London for further study, and requested the writer to prepare a review of the collection after mak- ing comparisons with related material in Doctor Abbott's collections i from neighboring islands. A report upon the avifauna of the whole chain of islands off the west coast of Sumatra would be welcome, but the writer does not wish to anticipate the results of Doctor Oberholser, who has been engaged upon the birds of this general region for so many years. For this reason he has confined himself to the Mentawi Group alone, more particularly to Siberut and Sipora, and has mentioned related forms from other islands only when in his opinion this would lead to a better understanding of the Mentawi birds. Chasen and Kloss, in their paper (cited above), named 11 new subspecies from Siberut and Sipora, three of which are not recog- nized in the present paper, but the writer ^ has described three addi- tional ones which are believed to be valid. Two of these are from Siberut and Sipora, the other from Sipora and the Batu Islands. This arrangement leaves 10 forms confined to the two northern i islands, but in the Mentawi Group as a whole there are 32 peculiar forms. The islands off the west coast of Sumatra generally are closely related in their avifauna to the mainland and Sumatra, as would naturally be expected, with a few well-differentiated species and many more or less well-marked races. As a rule, the forms from Simalur seem to be more strongly characterized than those from the remainder of the chain, with the possible exception of Engano. Messrs. Chasen and Kloss are to be congratulated upon their suc- cessful trip and on their published ornithological results ; their paper has left very little to be supplied here that is additional or new. s Ibis, 1926, pp. 269-306. • Proc. Biol. Soc. Wasiiington, vol. 40, 1927. pp. 95, 96. : ART. 4 BIEDS OF THE MENTAWI GROUP RILEY 6 For an account of the physical features of Siberut and Sipora and other details the reader is referred to the " Ibis " paper mentioned above. ANNOTATED LIST OF SPECIES TRERON CURVIROSTRA SMICRA Oberholser Treion curmrontra smicra Oberholser, Smiths. Misc. Coll., vol. 60, no, 7, 1912, p. 3 (Tana Bala Island, Batu Islands). Treron curvirostra Chasen and Kloss, Ibis, 1926, p. 273. Two males and one female, Sipora; six males and two females, Siberut. The Sipora and Siberut birds, compared with T. c. hypothapsina of Engano, have the greens above and below much more yellowish, with the yellow on the greater wing coverts brighter. The type of Treron curvlrostra smicra of the Batu Islands is an immature male not in full plumage (the describer evidently had only the one specimen) ; it is brighter and more yellowish than the Engano bird, but not as yellowish below as the adult males from Sipora and Siberut, It approaches the female from Sipora and Siberut in color of the underparts ; the head is washed with greenish, but is becoming gray. It would be unsafe to separate the Sipora-Siberut birds until we know what the adult of typical smicra is like. Treron curvlrostra pega of Nias is quite distinct, very pale below, greenish glaucous, washed on the chest with light grape green with a buffy tinge, and without the yellowish tinge on fchest as in smicra; there are also other differences. The female is without the buffy tinge on the chest, which is darker. Treron curvlrostra haliploa of Simalur resembles pega, but is darker below and the chest is washed with grape green, without buffy tinge. This form was evidently based on a single specimen. There thus appear to be four races of this species on the islands off the west coast of Sumatra, as below Treron curvirostra hypothapsina '^ from Engano. Treron curvirostra smicra,^ from Sipora, Siberut, and the Batu Islands. Treron curvirostra pega ^ from Nias. Treron curvlrostra haliploa ^ from Simalur. DENDROPHASSA VERNANS MESOCHLOA Oberholser Dendrophassa vemans mesochloa Oberholser, Smiths, Misc. Coll., vol. 60, no. 7, 1912, p. 2 (Nias Island). Treron vemans Chasen and Kloss, Ibis, 1926, p. 274. Two males, Sipora ; one male and one female, Siberut. ' Oberholser, Smiths. Misc. Colls., vol. 60, no. 7, 1912, p, 3. * Idem, p. 4. : ; 4 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 75 The specimens from Siberut and Sipora are intermediate between the Nias form and that from the Pagi Islands, but on the whole nearer to that of Nias. Considering only those forms of the species described from the Sumatran Avest coast islands, we have Demlrophassa vemans mesochloa^ from Nias. Dendrophassa vemans folioftila^ from North Pagi. Dendrophassa vertmns iniza^ from Simalur. The males of D. v. miza are more greenish on the back and are larger than the Nias bird. The wings of the males measure: 166, 163, 160.5 mm., and of the female (type), 156 mm. The culmen (from cere) is also longer; in males, 12, 12.5, 11.5; in the female 11 mm. The male of the Nias form is not so deep a green on the back and is smaller than the Simalur bird. Males measure, wing, 148.5, 157, 154, 151, 151.5, 151, 154.5, 154 mm.; culmen (from cere), 10-11.5 mm. Females, wing, 152 (type), 148, 148; culmen (from cere), 10-10.5 mm. One male from Siberut measures, wing, 161 ; one female. 147.5 mm. Two males from Sipora have the wings 153 and 156 mm. A male from Tana Bala, Batu Islands, is here assigned to the Nias form, with wing 149 ; culmen from cere, 11 mm. Males from the Pagi Islands are slightly lighter below than those from Nias, and this slight difference also holds in the females. There appears to be little or no difference in size, however. The wings of males measure: North Pagi Island, 148, 151.5, 161, 162.5 mm. ; culmen, from cere, 11-11.5 mm. Females from the same island the polioptila) have wing 154.5, 155, 157.5, 155, 150 (type of ; culmen, from cere, 10-11 mm. Males from South Pagi Island have the wing 146, 149 ; culmen from cere, 10-11 mm. A male from Engano is like the Nias bird ; it measures, wing, 157 culmen, from cere, 11.5 mm. The color differences between Pagi and Nias birds are only aver- age and not constant ; some of the Pagi males can not be distinguished from those of Nias.