New Guinea’s Islands in the Sky

Our fieldwork has focused primarily on New Guinea’s outlying mountain ranges. Ten such ranges of varying height and extent, detached from New Guinea’s central cordillera, occur along the island’s northern reaches. As of 1964, only half had been ornithologically explored. The other five were remote and difficult to reach overland, three of them so remote that it would have been impossible to reach the summits except by helicopter, and even the locations and elevations of their highest peaks were unknown. Such islands in the sky represent an ideal situation for studying species distributions over isolated patches of habitat: why some species are much better colonists (present on more isolated patches) than other species. JMD began exploring the unexplored outliers in 1966, and we began exploring them together in 1990. We have now explored all ten (1, 2, 3, 4).

Each site presents its own special challenges in terms of access and surveying. While local people clearly know the birds of the area, we were the first professional western biologists, let alone ornithologists, to explore the Van Rees and Kumawa mountains, and possibly the first humans to set foot on their summits, such is their extreme remoteness. Organizing the logistics for such expeditions is ‘interesting’. Despite our considerable experience, there is no planning for your helicopter pilot forgetting to pick you up after five weeks in the wilderness, at a site from which it would be impossible to walk out!

Our studies in the uplands of the Kumawas (3) discovered several undescribed taxa. However, our field methods focus on observation and sound-recording, so determination of their taxonomic status will have to await future sample collection.

Our studies of the Adelberts (2001, 2002, 2004, and 2006) in particular (see March Bull BOC) addressed the paradox of their harboring one of New Guinea’s most “spectacular, surprising, distinctive, and beautiful discoveries of modern New Guinea ornithology: Fire-maned Bowerbird Sericulus aureus.” Paradoxical, because ironically not a single other endemic species, and only a couple of undistinctive endemic subspecies, have been found in these mountains.

Even by the standards of New Guinea’s generally rugged mountainous terrain, the Adelberts rank as extremely tough and difficult for travel.  Our helicopter flights revealed no large flat areas; just tiny patches of land carved out for local farming. Such a rugged terrain has several consequences for ornithologists: no roads; no commercial logging – thankfully, thus the area remains largely covered in pristine forest. The terrain’s extreme difficulty and sustained warfare explain why the Adelberts remained unknown to Europeans for so long, despite their proximity to the German colonial capital of Madang – and why the discovery of the Fire-maned Bowerbird supposedly at “Madang” (actually, at medium elevations in the Adelberts) occurred so late and caused such astonishment (5).

The distinctness of this bowerbird may be due its evolution in considerable isolation from its allospecies Sericulus aureus, the Masked Bowerbird. No such allospecies occurs east of the Adelberts, and in the west it is separated from Masked Bowerbird by a wide geographic barrier (Fig. 2 March Bull BOC).  Strikingly, all other Adelbert upland populations are identical or similar to upland populations nearby on the Huon and the Central Range.  The easternmost record of Masked Bowerbird of which we are confident is not from the Central Range but from JMD’s collecting site of Mt. Turu in the North Coastal Range (6).

Thus, the range of Masked Bowerbird, as depicted in recent published maps of this taxon’s range, is in all likelihood incorrect. The only firm records known to us on the slopes of New Guinea’s main range are from the Weyland Mts. and Bernhard Camp.  Instead, in north New Guinea the Sericulus [aureus] superspecies is much more often recorded on north New Guinea’s outlying mountains than on the north slopes of the Central Range itself. Such revelations not only have important biogeographic implications but conservation considerations too.

The pandemic aside, our New Guinea studies continue.  We are as excited at the prospect of continuing to explore New Guinea as we were in our respective youths, oh so many years ago!

Linked paper: Jared Diamond, K. David Bishop “Avifauna of the Adelbert Mountains, New Guinea: why is Fire-maned Bowerbird Sericulus bakeri the mountains’ only endemic bird species?,” Bulletin of the British Ornithologists’ Club, 141(1), 75-108

Author Information

David Bishop (KDB) and Jared M. Diamond (JMD)