Measurements.—Measurements of 17 adult birds (9 males, 7 females, 1 unsexed) from Micronesia (Palau, Truk, Ponapé, Kusaie) and 10 adult birds (6 males, 4 females) from the Phoenix Group (Enderbury, Canton) are listed in [table 14].
Table 14. Measurements of Puffinus lherminieri dichrous
Table 14. Measurements of Puffinus lherminieri dichrous
| Locality | Wing | Tail | Exposed culmen | Tarsus |
| Micronesia | 203 (197-211) | 83.6 (77-89) | 27.9 (26-30) | 38.5 (37.5-40) |
| Phoenix | 197 (193-203) | 82.2 (79-85) | 26.3 (25-28) | 37.2 (36-39) |
Specimens examined.—Total number, 72 (44 males, 19 females, 9 unsexed), as follows: Palau Islands, AMNH—exact locality not given, 64 (Oct., Nov., Dec.); Caroline Islands, AMNH—Truk, 4 (June 15, 16)—Ponapé, 3 (undated)—Kusaie, 1 (April 25).
Nesting.—The Dusky Shearwater in Micronesia nests in holes on high, and usually isolated, coral cliffs. Owston's collectors, according to Hartert (1900:10), found a nest with one egg at Truk on June 16. The nest was in a hole four feet deep in the side of a cliff. The egg is white and measures 42 × 35. Yamashina (1932a:408) records the taking of one egg at Arakabesan, Palau Islands, on May 26. Coultas (field notes) gives an interesting account of nesting activities of this shearwater at the Palau Islands. He found the bird nesting on small islands of the group from October to December, 1931; however, he states that the natives told him that the bird nests throughout the year. Land crabs and shearwaters were often found together in the same burrow. Apparently the adult birds did not remain in the burrow with the young during the day. At Kusaie, Coultas was told by the natives that the adult birds were caught by tying the mandibles of the young together. When the parent birds approached and hovered over the young birds expecting their mouths to open, the natives had the opportunity to strike them down with clubs. Coultas collected six downy nestlings at Palau in November and December.
Remarks.—The first published account of this shearwater in Micronesia was apparently by Kittlitz (1858, pt. 1:358) when he recorded his "Schwärzlicher Sturmvogel" at Kusaie, according to Wiglesworth (1891a:79). Finsch (1875:44 and 1881b:113, 115) studied specimens taken by Tetens, Heinsohn, and Kubary at the Palau Islands and those taken by Kubary at Ponapé. Earlier, Hartlaub (1868:832) used some of these specimens from the Palau Islands to describe his Puffinus opisthomelas var. minor, which was destined to be placed in synonymy (Murphy, 1927:10). Oustalet (1896:54, 55) recorded specimens taken by Marche at Saipan in May, 1887, and at Rota in July, 1888. Oustalet referred to them as P. obscuras and P. tenebrosus, respectively. T. W. Gulick obtained undated skins at Ponapé. Hartert (1900:10) reported on specimens taken by Owston's collectors at Truk. In 1931, Coultas with the Whitney South Sea Expedition took one shearwater at Kusaie and a series of 64 skins at the Palau Islands. He failed to find birds at Ponapé and wrote that their scarcity there may have been due to persistent hunting of them by the inhabitants of the island. The NAMRU2 party obtained no information concerning the birds at Guam, Rota, or Truk, but at the Palau Islands observed shearwaters at sea approximately 6 miles east of Babelthuap Island on September 2, 1945.
Murphy (1927:6-15) revised the shearwaters of the Puffinus lherminieri group, and recognized several subspecies. P. l. dichrous was assigned a range consisting of Micronesia, the Phoenix Islands, and Nauru Island. The breeding range of P. l. polynesiae was given as the Samoan, Society, Tuamotu and Marquesas islands. Color differences between the two subspecies are very slight, and he separated them on the basis of the length of the exposed culmen as follows: P. l. dichrous 22.6-27 (26) in P. l. polynesiae 25.5-30 (28.9). In other measurements they closely resembled one another. At the time of his study, Murphy did not have the shearwaters from Micronesia collected by Coultas and actually did not have a large series from these islands. On studying this new material, I find the length of the exposed culmen of 17 adult birds from Micronesia (including 12 from the Palaus) to be 26-30 (27.9). In comparison with Murphy's findings, my measurements of Micronesian birds fall almost midway between the measurements which he recorded as characteristic of P. l. dichrous (from the Phoenix Islands) and P. l. polynesiae. The intermediate position of the measurements of the Micronesian birds, together with the absence of other distinguishing characters, suggests that these shearwaters belong to only one subspecies which consists of a group of isolated and variable populations. Unless the old specific name, obscuras of Gmelin, is revived, the name for the entire group in Micronesia and Polynesia would be P. l. dichrous. I agree with Murphy that the Bonin form, P. l. bannermani, is a well-defined subspecies.