3 The New York Years (1931–1953)

182 4 Ornithologist and Zoogeographer
connection on the basis of the percentages of the animals common to both. In
this, he pays no attention whatsoever (except in the general introduction) to the
fact, that these islands might be totally different in their ecology: If you compare
a savanna-covered island with a completely wooded island, you may get only
a slight agreement of the faunas, although the geological history of the two might
easily be the same. On the other hand, Rensch makes very little allowance for the
distribution across the open sea. My work on Polynesian islands and even such
islands, like Rennell and Biak , has convinced me that the open sea is not always as
much of a barrier as commonly supposed. As soon as two islands are fully settled
such as Batanta and Salawati, there is only very little exchange of individuals, but
as long as one island is full of open ecological niches, it will permit the settling
down of immigrants. This point has been largely disregarded by Rensch. I believe
you cannot make such definite statements as he does in many cases, neither do
I believe that all of the island connections have existed as postulated by him” (25
April 1939).
The distribution of birds in the Philippines is influenced by three main factors
(Delacour and Mayr 1946k): (1) Climate and vegetation, (2) former land connection
between islands, (3) proximity to neighboring areas. These factors jointly have
contributedtothespecialbirdfaunasofthevariousislandsandislandgroups.