The White-head 
71 
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 remarkable that so many of them should 
have retained common characters during the enormous period 
that must have elapsed since the formation of Cook Straits.” 
There is probably no doubt that the differences in the two 
representatives of these various species in the two islands are 
cine to long separation by the waters of Cook Strait, sixteen 
miles wide at its narrowest part, and ranging up to ninety, 
but the two species of fantail are common to both islands, 
though the black is much more plentiful in the South Island 
than in the North, and these two species interbreed without 
apparent change in their characteristic distinctions. It would 
be an interesting experiment to place representative birds of 
both species on some well-severed island, and see if they inter¬ 
breed, and if so, are the differentiating characteristics lost. 
It might be several generations before the difference, if any, 
would be detected. 
Both the white-head and the bush-canary, which go from 
place to place through the bush feeding in twittering flocks, 
were usually accompanied, or rather followed by a pair of 
saddlebacks. “The birds were never seen singly, says 
S. Percy Smith, (Tr. Yol. 43, p. 166), “but always in flocks of 
about thirty to forty, hopping about from branch to branch, 
with their little musical twitter. They were invariably accom¬ 
panied by a pair of saddlebacks, tieki (or tiaki), who seemed 
to act as guardians of the flock, giving the alarm, when any 
one approached, with their sharp notes. The word tiaki in 
Maori means 4 a Guardian,’ and this, no doubt, was the origin 
of the name.” It. is doubtful, however, if the presence of 
the saddleback was due to any other reason than an economic 
one: the flocks of smaller birds doubtless disturbed a great deal 
of insect life of whose presence the saddlebacks might take 
advantage; disturbed insects, too, that perhaps formed the 
prey of the saddleback but not of the others. Sncli associations 
