3 The New York Years (1931–1953)

180 4 Ornithologist and Zoogeographer
south, between Borneo and Celebes (Sulawesi) and between Palawan and the
Philippines in the north. This is “Wallace’s line” of most zoogeographers (Fig. 4.15).
A corresponding western limit of the Australo-Papuan Region follows the western
border of the Sahul Shelf which includes the islands of Aru, Misol and Waigeu
(“Lydekker’s line”). There is a third line where western and eastern faunal elements
of mammals and birds reach similar proportions of faunal balance (50 : 50%),
“Weber’s line” west of Tenimber, Buru and the northern Moluccas. Weber’s line
separates the islands with predominantly Indomalayan fauna in the west from
islands with a predominantly Papuan fauna in the east. Mayr (1944d) documented
that the shelf margins of both the Sunda land and Sahul land represent conspicuous
breaks in a general faunal transition zone between the Indomalayan and Australo-
Fig.4.15. Malay Archipelago, the contact zone between the Indo-Malayan and the Australo-
Papuan faunas. The shaded area in the west is the Asian (Sunda) shelf, and in the east lies
the Australian (Sahul) shelf. The area between the two shelves, never connected by a land
bridge, is referred to as Wallacea. The real border (line of balance) between the Asian and
the Australian faunas is Weber’s Line (from Mayr 1944d)