Travers.—On the Distribution of New Zealand Birds. 181 
I have already mentioned that the North Island possesses nine species 
peculiar to itself, of which Orthonyx albicilla is represented in the South 
Island by Orthonyz ochrocephala. The latter is a very different-looking 
and somewhat more robust bird than its North Island congener, but not- 
withstanding this difference in size and the greater differences which the 
two forms present in external characters, they both have precisely the same 
habits and notes. The differences between the external characters of the 
species of Petroica, Turdide, Apterygida, and Ocydromus peculiar to each 
of the main islands, though less manifest than in the case of the two species 
of Orthonyx, is very well marked, but in each of these instances also the 
habits and notes of the birds are the same. In the case of the Corvida, 
the North Island species is only distinguished from the South Island one 
by its slightly larger size and by the eolour of the wattles, but in this 
instance also the notes and habits of the birds are identical. It will have 
been observed by those who have seen them in their natural state, that, 
with the possible exception of Pogonornis cincta, all the birds of flight 
peculiar to the North Island, and with the exception of the two species of 
Nestor, all those peculiar to the South Island, which frequent forest habitats 
in the respective islands, are birds which never voluntarily rise above the 
level or move outside the limits of the forests in which they dwell, and the 
chances are, therefore, very remote that any of them should pass, in numbers 
at all events, across the waters dividing the two islands. 
The same observations may be applied to a large proportion of the 
species common and peculiar to the two islands, rendering it remarkakle 
that so many of them should have retained common characters during the 
enormous period that must have elapsed since the formation of Cook 
Straits. 
The non-occurrence of Heteralocha acutirostris in the South Island may 
excite surprise; but it must be remembered, in the first place, that this is 
one of the birds which never voluntarily rises above the level or passes 
outside of the limits of the forest in which it lives, and in the next, that 
its range, even in the North Island, is restricted to mountain districts so 
placed that the only winds of sufficient strength to overcome the efforts of 
stray birds to return to their own special abode, would prevent their 
crossing the dividing waters. The restriction in the range of this bird 
is, however, not so surprising as that which occurs in the cases of Nestor 
occidentalis and Nestor notabilis in the South Island, seeing that, apparently, 
the very same natural conditions as those which characterize their respec- 
tive special habitats, extend over a large portion of both islands. We are 
but little aware of the circumstances which operate in causing a restriction 
in the range of any particular species, or which may lead to the local 
