3 The New York Years (1931–1953)

176 4 Ornithologist and Zoogeographer
Fig.4.13. Distribution of the Pied Bushchat (Saxicola caprata) in the Malay Archipelago and
in New Guinea from where this open-country species of Asian origins has reached only
the Bismarck islands of New Britain and New Ireland and the nearby recently defaunated
volcanic islands of Long and Uatom. Like most other open-country colonists of Northern
Melanesia, it has scarcely differentiated: the Bismarck populations still belong to the same
subspecies as the New Guinea source population. From Mayr and Diamond (2001, map 31)
and bird sketches from MacKinnon and Phillipps (1993, plate 71)
steppe had a much wider distribution in New Guinea than now” and in a letter to
Erwin Stresemann dated 25 April 1939 discussing the distribution pattern of the
Pied Bushchat (Saxicola caprata; Fig. 4.13) Mayr wrote: “I believe that at some time
in the past there was a drier zone along the north coast of New Guinea which was the
immigration route of this form. The three species which I discovered in the Arfak
Mountains: Megalurus timoriensis, Acrocephalus arundinaceus and Lonchura vana
are an indication of this line of immigration. There are quite a number of the
savanna species which have not reached Australia. I am fairly convinced that these
species reached eastern New Guinea via the Moluccas and western New Guinea.
These species are Saxicola caprata, Merops philippinus, and Lanius schach” (see
Haffer 1997b: 509). Saxicola caprata probably did not have to fly across the ocean
from the Philippines to eastern New Guinea, as tentatively indicated on Fig. 4.13,
but was able to hop from one island to the next through the Moluccas and western
New Guinea during a cool-dry climatic period of the recent geological past, when
these regions were partially covered with open nonforest vegetation.
Similarly, the fact that the grasslands of the island of Guadalcanal, one of the
Solomon Islands, are the home of two endemic subspecies of birds (a finch and