Birds of paradise, biogeography and ecology in New Guinea: a review

912 M. Heads
Milne Bay islands
The islands of the D'Entrecasteaux and Louisiade Archipelagos
form an eastward extension of the New Guinea orogen
possibly related to the Owen Stanley terrane (Pigram &
Davies, 1987) and the D'Entrecasteaux islands include active
metamorphic core complexes (Tregoning et al., 1998). The
low Trobriand Islands to the north also lie within the belt.
Birds of paradise are represented in this region only by three
species of Manucodia. M. keraudrenii hunsteini is endemic
to the three D'Entrecasteaux islands. M. comrii Sclater is
known only from these same islands (M. c. comrii) and, at
the family's limit, the Trobriand Islands (M. c. trobriandi
Mayr); there is a spreading centre in the Woodlark Basin
(de Boer & Duffels, 1996a; Tregoning et al., 1998) and these
ranges may have been split apart by the opening of the basin.
Finally, M. atra Lesson has an endemic race, M. a. altera
Rothschild and Hartert, on Sudest ( ˆ Tagula) I. in the
Louisiades, but is not present on the D'Entrecasteaux or
Trobriand Islands.
It is striking that the only islands off New Guinea that
birds of paradise occur on ± northern Moluccas, Western
Papuan Islands, Japen, D'Entrecasteaux, Trobriands, and
Sudest ± all lie within the New Guinea orogen (Fig. 2). The
islands of Manam, Karkar and the Bismarck Archipelago lie
outside this belt and do not have birds of paradise. A very
similar distribution on the mainland and the Milne Bay
Islands, but absent from the Bismarck Archipelago, is seen in
the snake Tropidonophis aenigmaticus Malnate (Fig. 38).
Restricted island endemics, such as Semioptera and
Lycocorax on the Moluccas and Manucodia atra altera on
Sudest, are usually assumed to have been derived from a
widespread population on the mainland. However, the
island endemics may once have had a much more extensive
distribution on now-sunken land, for example around
Sudest, which is `obviously submerged' (LoÈ f¯er, 1977). In
this case birds that are currently `mainland' and `island'
forms are probably descendants of a common ancestor
formerly widespread over very different Mesozoic and
Tertiary geography. Likewise, areas of ocean ¯oor in the
Gulf of Papua, such as the Eastern Fields Fan (50,000 km 2 )
between Port Moresby and the northern end of the Great
Barrier Reef, have been subsiding ever since the Coral Sea
began rifting open in the Miocene (Mutter, 1975). This
could explain biogeographical connections between the
trans-Fly and Port Moresby regions `cutting the corner'
across the Gulf of Papua, seen for example in several snakes
mapped by O'Shea (1996).
The island taxa cited above include distinctive endemic
genera, as well as barely differentiated taxa, but the same
principle may apply. Minor morphological and molecular
differences may re¯ect ancient but rapid and minor evolutionary
divergence followed by a long periods of stasis, with
possible geographical convergence of populations on converging
terranes.
Rand & Gilliard (1967) cited many species, for example in
Eos (Fig. 15), which `favour' small islands. But perhaps these
taxa have no choice if small islets form the only land currently
available in their respective regions. The islets may represent
the last land in an area of subsidence, and competition from
related forms prevents establishment in neighbouring territory.
These birds survive on small islets and atolls because,
®rstly, they were already in the region in a prior geography,
and secondly, because they either possessed the necessary preadaptations
for this ecology or were able to adapt. The vast
majority of small islet taxa around New Guinea are not found
on all the many islets available, but only those in particular
regions. This implies that something other than the small islet
ecology is determining the distribution.
Northern limits of birds of paradise and bowerbirds
Despite being on the western Papuan Islands and the Milne
Bay islands, no birds of paradise or bowerbirds are known
from the offshore islands of Biak, Karkar, Manam, New
Britain, or New Ireland, all of which provide suitable habitat:
hills with closed rainforest. The island of Karkar, for example
(Fig. 4), is 25 km across and 1850 m high, largely covered in
rainforest and only 15 km offshore. Yet there has never been
a single record of a bird of paradise or bowerbird there. New
Britain is a much larger island, 90 km off New Guinea. A
surprising 70% of the species on the part of New Guinea
opposite New Britain are not represented on New Britain
(Mayr, 1940). Gressitt (1982b) frankly admitted that the
absence of many New Guinea groups from the Bismarck
Archipelago, `in spite of proximity and island steppingstones',
is `puzzling'. In fact the avifauna of these islands is
both rich (Coates, 1990) and quite different from that on the
mainland ± many ¯oristic and faunistic works (e.g. Rand &
Gilliard, 1967; Beehler et al., 1986) are logically limited to
the mainland taxa. Because the offshore islands are so close it
seems that `dispersal' in the sense of physical movement, or in
this case lack of dispersal, has nothing to do with the major
faunistic difference. On the other hand, it is surely not a
coincidence that the northern boundary of the New Guinea
orogen runs along the north coast and marks the mutual
boundary of the two faunas, including the northern limit of
Paradisaeidae and Ptilonorhynchidae.
The distinctive fauna of Karkar and the other fringing
islands includes birds such as Charmosyna rubrigularis
(Sclater), Macropygia mackinlayi (Ramsay), Cacomantis
variolasus fortior (Rothschild & Hartert), Ducula pistrinaria
Bonaparte, Monarcha cinerascens Temminck and Myzomela
sclateri Forbes (maps in Coates, 1990). These are all on
Karkar and several of the other northern islands (New
Britain, etc.) but are not on the New Guinea mainland,
where they are replaced by allied forms. At subspecies level
Gallicolumba b. beccarii (Salvadori) is in the mountains
throughout New Guinea, and G. b. johannae (Sclater) is on
Karkar Island and the Bismarck Archipelago. Megapodius
freycinet (Gaimard) shows the boundary well, with
M. f. af®nis Meyer in northern New Guinea and M. f.
eremita Hartlaub on Manus, Long Island, Siassi (ˆ Umboi
or Rooke) Island, New Britain, and the Solomon Islands.
Karkar Island, on the biogeographical boundary between the
two, has a `mixed population' (Rand & Gilliard, 1967).
Ó Blackwell Science Ltd 2001, Journal of Biogeography, 28, 893±925