On they went through the tropical forest, along the swiftly flowing river, passing now and then little stretches of open pampas or grassy plain, where there is excellent pasturage for cattle. At night they halted at an island; the boatmen always prefer to pass the nights on islands when journeying along the river, as they are then much more secure against the wild Indians who might do them harm. Most of the hostiles are without boats, and even when possessing them they are cautious about venturing on the islands for the purpose of making an attack. They greatly prefer to have a safe line of retreat behind them in the shape of the forest, where pursuit is next to impossible. At their second day's nooning it was Fred's turn to make a discovery in ornithology. Several times they had heard the shrill voice of the parrot, but had not succeeded in detecting the bird that made it; at the halting-place we have just mentioned Fred saw two or three parrots among the trees just as his boat swung to the shore, but they flew away at the approach of their disturbers and disappeared. As soon as they had landed, the youth followed in the direction the birds had taken, and was fortunate enough to see them again; evidently they were near their nesting-place, but they did not manifest any willingness to invite the stranger to see them at home. [Illustration: TOUCAN. PARROTS.] The hooked bill of the parrot is as inconvenient in nest-making as the great beak of the toucan; the philosophical bird accepts the situation, and rears its young in a hollow tree, like its huge-billed friend. Parrots are more numerous than toucans and also more noisy; probably for these reasons they are seen quite frequently, while the discovery of a toucan is not easily made. The Doctor said a traveller might make the descent of the Amazon without seeing one of the latter birds, while he would encounter the parrot very often. Consequently Frank might feel proud of what he had seen the day before, and but for the accident of stumbling upon the locality of the nest he would not have been thus favored. Occasionally parrots and toucans are found together; both are gregarious, and the same may be said of most of the birds of South America. To the parrot family belong the true parrots, paroquets, and macaws. Paroquets go in flocks, while the parrots always fly in pairs, though they flock together in large numbers on the trees. A few Indian tribes consider the macaw sacred, and it is called by some of them "the bird of the sun."