Fig. 17. Tropic Bird on Nest. Not only does the bird fauna crowd all the available space on the ground, and in the bushes, and swarm in the air above, but still another vast multitude burrows under the sandy surface, forming a subterranean population that in itself would make the island of peculiar interest to the naturalist. Nor does the human visitor long remain in ignorance of this fact, for he has taken but a few steps anywhere among the bushes before lie suddenly joins the 'submerged tenth' in a most undignified and 
Fig. 18. 'Bush Gannet' on Nest. precipitate manner, and is struggling waist deep in the yielding sand, an unwelcome invader of the home of the shearwater. This experience has the charm of novelty at first, but becomes exasperating after a score of repetitions in the course of an hour, with the perspiration streaming down one's face and the sand packed inside of one's shoes and clothing. How many scores or hundreds of thousands of these burrowing Procellaridæ there are on the island it is vain to estimate; but there are four or five species, and the entire surface is fairly undermined by their tunnels 
Fig. 19. 'Sand Gannet' with Egg and Young. and burrowings. Their notes are melancholy beyond expression, being a distressful moaning, sometimes reminding one of the less romantic yowling of the night wandering cat.
As one walks among the bushes be is from time to time greeted with most strident and piercing screams from nesting tropic birds, rarely beautiful creatures, pure satiny white, the wings and tail mainly black, the two central tail
