262 REPTILES AND BIRDS. 
The appearance of these birds announce, as we have said, that: 
the navigators have entered the torrid zone, as they rarely go beyond 
the limits of this region. It sometimes, however, pushes out to sea 
to a distance of a hundred leagues. When they are fatigued, aided 
by their large webbed feet, they rest upon the waves. Like many 
other ocean birds, their peculiar organisation prevents them settling 
on the ground from choice. T hey, therefore, skim continually over 
the surface, on which they obtain their food, which consists of fish 
and molluscs. To enjoy a state of quiescence, the immense spread 
Fig 96.—Tropic Bird. 
of their wings forces them to choose an elevated perch, such as the 
top of a tree or the summit of a rock. When worn-out by fatigue, if 
they settle on the water, they are forced to wait until they are lifted 
on the crest of a wave before they can again take flight. Their mode 
of flying is peculiar, for they communicate to their wings a kind of 
quivering motion. 
These birds seek remote and solitary islands for the purpose of 
breeding. ‘They build their nests in trees, or in the clefts of rocks, 
but always in some position difficult of access. They lay two or 
three eggs. ‘The young ones, when just hatched, owing to their 
Soe down, bear a considerable resemblance to powder- 
puffs. 
