maximum, but sea levels were >100 m lower as little as ~18,000 years ago during the last glacial maximum. The Indonesian archipelago is characterised by extensive shelf areas of shallow sea, especially (but not exclusively) in its western part. During glaciations and global drops in sea level, enormous areas of land form across the archipelago and lead to connections between land masses we now see as islands. In our region, Pleistocene sea level fluctuations are one of the most important biogeographic factors, and bathymetry (research into sea depths) has become a useful tool for ornithologists to predict faunal connections between islands across the region (Figure 1). While we have known about the effects of Pleistocene glaciations for a while now, there are two aspects about them that are still insufficiently appreciated in the ornithological community: (1) their frequency, and (2) their recency. As regards their frequency, Pleistocene drops in sea level have recurred so many times, and for such extended periods of time, that it is almost biogeograph-
Figure 1. Bathymetric and topographic map comprising most of our region (minus easternmost parts, such as Kai). Green shades denote various elevations of currently exposed land. Blue shades denote various depths of current sea and ocean. Yellow and ochre shades denote areas currently submerged by shallow sea (=shelf) but exposed as land at various periods during Pleistocene glaciations in the last ~2 million years. At glacial maxima, such as during the ‘Last Glacial Maximum’ (LGM) at 18,000–21,000 years ago, the extent of land was greatest, leading to the formation of the Sundaic subcontinent that has repeatedly been connecting Borneo, Java, Sumatra, Bali and the South-east Asian mainland. Note also the smaller but equally important land connections between various Wallacean islands (such as Sumbawa and Flores, or Sula Islands and Banggai Islands) (modified from Sathiamurthy & Voris 2006). 95
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ically inappropriate to think of some land masses as ‘islands’. Land masses such as Sumatra and Java have been connected to the Asian mainland far more often – and for longer – than they have been separated as islands. Modern humans’ perception of these regions as islands is based on our existence during a less typical era (the peak of an interglacial) that is marked by their brief severance from mainland Asia before they become reconnected only a few thousand years later. As regards the recency of drops in sea level, the last glacial maximum occurred as little as 18,000 years ago, but land connections in particularly shallow shelf areas would have been even younger by a few thousand years. Modern humans walked from the Malay Peninsula to Sumatra and Java, or from Sulawesi to Buton. Animals and plants from these land masses would have been closely connected, too.
Wallace’s Line In biogeographic terms, the region comprises two halves split by an iconic biological boundary the name of which commemorates one of the region’s greatest explorers: Sir Alfred Russel Wallace. This line separates the Asian continental shelf in the west from the more easterly Wallacea, a region of deep-sea islands (again named after Wallace) that is tucked in between the Asian and Australo-Papuan continental shelves and is characterised by an avifauna of mixed Asian and Australo-Papuan descent. Without a knowledge of the distribution of deep-sea trenches or shallow shelf water, it was Wallace who first identified the difference in the mammals and birds of the island of Bali to those of the island of Lombok situated only 21 km to the east. In his book The Malay archipelago he says “In Bali we have Barbets, Fruit thrushes and Woodpeckers; on passing over to Lombok we see these no more, but on Lombok we have an abundance of Cockatoos, Honeysuckers, and Brush-turkeys which we do not see in Bali or further west.” Recognising similar differences between the wildlife of Borneo and Sulawesi, he drew a line between islands that was later named by Huxley as ‘Wallace’s Line’. Subsequent exploration by Richard Lydekker identified a similar distinction between the birds and mammals of Wallacea and those of New Guinea, with the latter being defined by species that were purely of an Australo-Papuan origin while the former exhibits a pronounced Asian element. This line subsequently became known as ‘Lydekker’s Line’ and now forms the eastern boundary of the region covered by this guide. Expanding on these distinctions further, the Indonesian archipelago can broadly be described as having four geographically distinct regions: west of Wallace’s Line lie the Greater Sundas, whereas Wallacea to the east of Wallace’s Line comprises the Lesser Sundas, Sulawesi and the Moluccas. Below these regions are considered in greater detail:
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The Greater Sundas comprise the islands that lie on the Sunda Shelf. This area is essentially an extension of the Malay Peninsula and the South-east Asian mainland, and at most times during the Pleistocene has formed its own ‘Sundaic subcontinent’ (sometimes referred to as ‘Sundaland’). However, at other times (such as now) the Greater Sundas constitute an archipelago consisting of some of the largest islands on Earth. The main islands in this group, Sumatra, Borneo, Java and Bali, all have mountains over 3,000 m, with the highest being Mt Kinabalu on Borneo at 4,095 m (see table below). The continental Asian nature of the Greater Sundas is reflected in the bird families found here, which are of a typically South and South-east Asian (‘Oriental’) affinity. The constant land connections among the Greater Sunda Islands are also reflected in
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