_Globecera oceanica ratakensis_ Takatsukasa and Yamashina, Dobutsu.
Zasshi, 44, 1932, p. 221. (Type locality, Aruno.)
_Columba australis_ Chamisso, in Kotzebue's, Voy. "Rurick," 3,
1821, p. 157 (Radak).
_Carpophaga oceanica_ Finsch, Ibis, 1880, p. 331 (Arno);
Wiglesworth (part), Abhandl. und Ber. Zool. Mus. Dresden, no. 6,
1890-1891 (1891), p. 52 (Arno); _idem_, Ibis, 1893, p. 211
(Marshalls).
_Globicera oceanica oceanica_ Momiyama (part), Birds Micronesia,
1922, p. 5 (Arno); Kuroda (part), in Momiyama, Birds Micronesia,
1922, p. 55 (Arno).
_Globicera oceanica ratakensis_ Hand-list Japanese Birds, rev.,
1932, p. 190 (Arhno, Wotze); Mathews, Ibis, 1933, p. 87 (Aruno,
Wozzie).
_Ducala oceanica ratakensis_ Peters, Check-list Birds World, 3,
1937, p. 44 (Arno, Wotje); Hand-list Japanese Birds, 3d ed., 1942,
p. 212 (Arhno, Wotze); Amadon, Amer. Mus. Novit., no. 1237, 1943,
p. 12 (Arno, Wotje); Mayr. Birds Southwest Pacific, 1945, p. 289
(Arno, Wotje).
_Geographic range._--Micronesia: Marshall Islands (Radak
Chain)--Wotje, Arhno.
_Characters._--Takatsukasa and Yamashina (1932:221) describe this
subspecies as follows, "This form differs from all other forms of
_Globicera oceanica_ by its smaller size, more bronze-sheen on the
back, more vinaceous grey on the breast and duller brown on the
abdomen." On examining two specimens from Arno in the collection
of the Museum of Comparative Zoölogy, Amadon (1943:12) writes that
he finds no distinguishing color characters between _D. o.
oceanica_ and _D. o. ratakensis_. He also questions whether there
is any difference in size between the two populations.
_Measurements._--Measurements are listed in table 27.
_Remarks._--Chamisso (1821), the naturalist on board the ship "Rurick,"
was the first person to write of the pigeon in the Radak Chain of the
Marshall Islands. The ship visited this area in 1817. Finsch (1880b)
published an account of the bird when he visited the area about 1880.
Takatsukasa and Yamashina (1932:221) described this bird as new on the
basis of an examination of nine skins taken at Arhno and Wotje.
_Evolutionary history of Ducula oceanica in Micronesia._--The
distribution and evolutionary history of _Ducula oceanica_ have been
treated by Mayr (1940) and Amadon (1943). These authors place _D.
oceanica_ within a superspecies containing _D. pacifica_ (Melanesia to
Samoa and Cook Islands), _D. aurorea_ (Society Islands), _D. galeata_
(Marquesas Islands), and possibly other species in Papua and Malaysia.
According to Mayr (1942b:fig. 7), _D. pacifica_ is the species which is
ancestral to other species of pigeons in Oceania. Apparently _D.
oceanica_ was derived from this ancestral stock and reached Micronesia
via the Ellice and Gilbert islands. Records of _Ducula_ were obtained in
the Gilbert Islands in the days of exploration; Amadon (1943:11)
tentatively refers these to _D. o. oceanica_.
The irregular distribution of _D. oceanica_ in the islands of Micronesia
and the fact that the bird exists on both "high" volcanic islands as
well as on "low" coral atolls suggest that the present population may be
a remnant of a once more widely distributed one. The fact that _D.
oceanica_ may be divided into several subspecies shows that a greater
amount of geographic variation has occurred as compared with its
probable ancestral stock, _D. pacifica_, which is virtually
undifferentiated over most of its extensive range. The pigeon of
Micronesia has a more rounded wing than that of _D. pacifica_, which
might, as Amadon has suggested, cause the bird to be more sedentary and
lend itself more readily to differentiation through geographic
isolation. _D. pacifica_ is known to fly from island to island. As shown
by the measurements in table 27, the length of wing of _D. oceanica_
differs, in the various insular populations, being longer in the west
and shorter in the east. This cline has been discussed by Amadon
(1943:11).
It is interesting that _Ducula_ or some other large pigeon has not
become established in the Mariana Islands. _Ducula_ is present at Yap
and Truk, which are not very distant from Guam. Another tropical pigeon,
_Columba vitiensis_, has extended its range northward and reached the
Bonin Islands; probably it arrived there via the Philippines or the Riu
Kiu Islands. Thus, there are representatives of large pigeons on islands
to the southeast, south, west and northwest of the Marianas, but none
has become established in the Marianas themselves.
=Streptopelia bitorquata dusumieri= (Temminck)