Distribution, taxonomy and evolution of the gardener bowerbirds, Amblyornis spp, in eastern New Guinea with descriptions of two new subspecies (Contributions to Papuasian Ornithology No.2)

Abstract

Amblyornis macgregoriae and A. subalaris are effectively altitudinally allopatric on both scarps of the Owen Stanley Range. The hitherto poorly known distribution of the two species in the eastern Owen Stanley Range is documented in some detail. Both species meet between altitudes of 1,200 and 1,400 m, with A. macgregoriae occurring in primary mixed montane and Nothofagus-forest above, and A. subalaris in primary fagaceous hill-forest below. The juxtaposition of A. macgregoriae bowers on ridges and of A. subalaris bowers on slopes below the crests of ridges in areas of abutment suggests competition between the two species; altitudinal displacement of A. subalaris by A. macgregoriae is inferred.

The evolution and distribution of A. macgregoriae and A. subalaris are interpreted in terms of alternating disjunction and conjunction of one ancestral stock brought about by the altitudinal expansion and contraction of forest-zones during climatic oscillations of Pleistocene times. The present grouping of subspecies of A. macgregoriae in eastern New Guinea is probably the result of the most recent (post-glacial ) isolation of various populations by passes of low altitude and valleys of alien habitat. A. subalaris is monotypic.

Two new subspecies are recognized: A. macgregoriae kombok, in the Kubor-Mt Hagen-Bismarck Ranges, and A. m. nubicola, in the extreme eastern Owen Stanley Range.