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A New Cuckoo-Shrike from the Bismarck Archipelago

Charles G. Sibley
4 (July-August)
From Field and Study
Online Text

A New Cuckoo-shrike ‘from the Bismarck Archipelago.-The existence of a distinct race of the cuckoo-shrike, Edolisoma morio, in the islands of the St. Matthias Group, Bismarck Archipelago, was suspected by Hartert (Nov. Zool., 31, 1924:272) but he hesitated to name the form since no adult female specimens were then available. With the collection of three females from Emirau Island in this group, the solution of the problem is now possible. The form in the St. Matthias islands proves to be separable from adjacent populations and I propose for it the name

Edolisoma morio matthiae, new subspecies

Type.-Adult female, no. 90187 Mus. Vert. Zool., from Emirau Island, St. Matthias Group, Bismarck Archipelago, collected May 28, 1944, by Charles G. Sibley; orig. no. 2239.

Diagnosis.-Adult female similar to Edolisoma morio heinrotlzi of New Britain but paler, especially on underparts which are Light Ochraceous Buff in matthine and Ochraceous Tawny in Wnrothi.

Range.-Emirau (Storm or Squally) and Mussa.u (St. Matthias) islands in the St. Matthias Group.

Specimens exemined.-Three females and three males from Emirau and a fourth male from Mussau have been examined. In addition to these an immature bird recorded by Hartert (Zoc. cit.) is known. The species was not detected on Tenth Island. On both Emirau and Mussau it is an uncommon species. In addition to the specimens taken the only individuals encountered were adult males observed on Mussau on August 25 and 29, 1944.

From the females of E. m. remotum of New Hanover, the St. Matthias birds are distinguished by their barred underparts and paler coloration. In remotum the underparts are clear Ochraceous Tawny without the black transverse barring characteristic of the other races in the Bismarck Archipelago. From both E. m. rooki of Rook Island and E. m. admiralitatis of the Admiralty Islands, nzutthiae is separated by its larger size and paler coloration.

This species exhibits much greater geographical variation in the females than in the males. Hellmayr (Jour. fiir Omith., 2, 1929:41-70) has designated this condition by the term “heterogynism.” Mayr (Systematics and the Origin of Species, 1942:SO) presents a summary of heterogynism and points out that the phenomenon is most often found in species in which the females are brownish or grayish and the males are black or darkly colored. This is exactly the condition in Edolisoma motio which exhibits a high degree of sexual dimorphism, the females in general being rusty brownish and the males dark slaty-blue or blue-black. The males of the races in the Bismarck Archipelago do not vary appreciably in color although they parallel the females in the degree of variation in size.

For the loan of comparative material I am indebted to Dr. Ernst Mayr and the American Museum of Natural History.-CHARLES G. SIBLEY, Museum of Vertebrate Zoology, Berkeley, California, June 6,1946. 


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