EEP Crowned pigeon number 4

EEP STUDBOOK CROWNED PIGEONS
Lowland rainforest occurs along the entire coast of New Guinea, being broken in a few places
by anthropogenic grassland or eucalypti savanna. However, at the moment large areas of
tropical rainforest occur only in three regions:
(1) The vast Fly Platform south of the Central Ranges, extending from about Etna Bay at the
neck of the Vogelkop to Hall Sound on the SE peninsula, home of the Scheepmakers
crowned pigeons
(2) In the west, the Vogelkop peninsula, where the common crowned pigeons occurs, and
(3) In the north, the watershed of the Mamberambo River and its tributaries and adjacent
coastal plains, and the Sepik and Ramu basins. In this area the vicoria’s crowned pigeons
occur.
These three lowland areas are isolated from eachother by two geographical barriers: (1) the
Central Ranges, which separates the northern from the southern lowlands, consists of high
mountains (3000-5000m) and are crossed by only a few passes at about 1200-2000m; thus the
important zones of contact between northern and southern faunas are at the far eastern and
western ends of the range, (2) the mountainous isthmus between the Vogelkop and the main
body of the island. In the Pleistocene, there was also a major change in rainfall pattern due to
reduced precipitation. Much of the tropical rainforest along the coast is replaced by savanna
and sclerophyl vegetation. This left remnant pockets of rainforest only where the precipitation
remained high (Pratt, 1981). Thus by the mountains and the reduced precipitation, three
geographical regions into which many lowland birds segregate were separated by barriers
defined by low rainfall and/or mountains. The populations were confined to regional refuges
of humid forest, segregated from other areas by broad belts of inhospitable habitat during
periods when rainfall was reduced (Beehler, et al., 1986). If the drier zones were in fact gaps,
then the Fly, Vogelkop, Geelvink, and Sepik and Ramu rainforests would have become
isolated tracts (Pratt, 1981). Thus speciation may have occurred in a typical geographic
fashion, during dry and cool Pleistocene conditions, when ranges were more fragmented than
they are today (Beehler, et al., 1986). When the climate changed again and the rainforests
expanded in response to higher precipitation, many birds followed the forest out of the
refuges. This range expansion continued until allopatric populations came into contact once
again. This is said to be the case for crowned pigeons: each species of crowned pigeons
occupies one of the main distributional centers for lowland birds. In the Fly Platform the
scheepmakers crowned pigeon occurs the common crowned pigeon at the Vogelkop and the
victoria’s crowned pigeon at Geelvink Bay. In the Siriwo River region of northwestern New
Guinea Goura victoria and Goura cristata meet and hybridize (Goodwin, 1983). In the Sepik-
Ramu area crowned pigeons do not occur. (Pratt, 1981). There, they probably became extinct
because of few numbers or other ecological reasons, like food abundance or climate.
Most of the islands, where crowned pigeons occur, are co-called ‘land-bridge islands’:
Waigeo (or Waigeu), Yapen, Salawati, Misool and Batanta. Land-bridge islands were in the
past connected to the mainland (New Guinea), but since the sealevel has risen, they became
isolated (Diamond, 1973). This development has taken place only recently.
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