I collected one hundred species of land-birds in the Aru Islands, and about eighty of them, have been found on the mainland of New Guinea.

Among these are the great wingless cassowary, two species of heavy brush turkeys, and two of short winged thrushes; which could certainly not have passed over the 150 miles of open sea to the coast of New Guinea.

This barrier is equally effectual in the case of many other birds which live only in the depths of the forest, as the kinghunters (Dacelo gaudichaudi), the fly-catching wrens (Todopsis), the great crown pigeon (Goura coronata), and the small wood doves (Ptilonopus perlatus, P.aurantiifrons, and P.coronulatus).
Now, to show the real effect of such barrier, let us take the island of Ceram, which is exactly the same distance from New Guinea, but separated from it by a deep sea.

Cut of about seventy land-birds inhabiting Ceram, only fifteen are found in New Guinea, and none of these are terrestrial or forest-haunting species.

The cassowary is distinct; the kingfishers, parrots, pigeons, flycatchers, honeysuckers, thrushes, and cuckoos, are almost always quite distinct species.