120 BIRD LIFE ON ISLAND AND SHORE 
tion of species. Owing to local conditions there 
seemed to be occurring certain modifications of 
normal habits—habits that hardly strike us as 
requiring explanations when we are born to them, 
accepted with as little concern as are the daily 
miracles of light and growth. 
One of the modifying environments was the 
nightly shower of sea-fowl, a fall which continues 
during the whole breeding season of the resident 
land birds. Thus on the mainland, where no fall 
of Petrel occurs, the Tui, the Bellbird, and the 
Robin, I believe, habitually build nests open to 
the sky. On Kotiwhenu the Tui’s nest is placed 
where protection is afforded by stout, small, 
covering boughs, branched clusters of twigs suffi- 
ciently stiff to fend off a falling bird. More pro- 
nounced is the effect of the Petrel fall on the 
nesting habits of the Bellbird. Of the two dozen 
Bellbirds’ nests known to us on Kotiwhenu, half 
were built in cavities and tree holes; the others, 
as in the case of the Tui, placed where other pro- 
tection was obtainable. Thus in some degree the 
idea of shelter for their nests in tree holes and 
chinks is permeating this breed. The Bellbird is 
a migrant. Undoubtedly there is free and con- 
stant communication with the mainland; equally 
certain is it that. a large proportion of Bellbirds 
of this region breed, not on the barren mainland, 
but on the islands fertilised by centuries of guano 
