KOTIWHENU 123 
mon in the forests of the mainland, a climber of 
timber, almost like the Rifleman. We must next 
note the breed on some islet more thickly wooded, 
less heavily coated in peat, and therefore less 
densely stocked with Petrel than Kotiwhenu. 
Lastly, we must view it on Kotiwhenu, positively 
a ground bird. The factors of change are inability 
to escape from a limited area, and the increasing 
persecution of another bird. The Robin is the 
chief instrument by which nature seems to be 
shaping out a new species of Xenicus. 
Before the arrival of the European, Robin and 
Bush Wren were alike plentiful in the forests of 
the mainland. Ample room was there, and verge 
enough for both in the woods that then covered 
the country. Food was plentiful, nesting sites 
abundant. It was impossible that the two species 
could clash, or that the one could affect the other. 
We have now to consider conditions obtaining 
on the considerable island Te Puka, where Wrens 
are abundant. Though also a breeding-ground 
for Petrel, it is covered almost everywhere with 
ferns and sedge and ample undergrowth; only 
on certain slopes has the vegetation been eroded 
with bird traffic. Both Robins and Bush Wrens 
abound, but owing to the greater area of the 
land surface and the quantity of cover, the two 
species are not perpetually in each other’s pres- 
ence. The Wren is less furtive and shy. Though 
