1. All the actions of animals are employed either in sexual intercourse, or in rearing their young, or in procuring food for themselves, or in providing against excessive heat and cold, and the changes of the seasons. For they all have naturally a sensitiveness respecting heat and cold, and, like mankind, who either change their abodes in cold weather, or those who have large estates, pass their summer in cold countries and their winter in warm ones; so animals, also, if they can, migrate from place to place. Some of them find protection in their accustomed localities, others are migratory; and at the autumnal equinox, escape at the approach of winter, from the Pontus and other cold places; and in spring retreat again before the approach of summer from hot to cold countries, for they are afraid of excessive heat. Some migrate from places close at hand, and others from the very ends of the earth. 2. The cranes do this, for they travel from Scythia to the marshes in the higher parts of Egypt, from which the Nile originates. This is the place where the Pygmies dwell; and this is no fable, for there is really, as it is said, a race of dwarfs, both men and horses, which lead the life of troglodites. The pelicans also are migratory, and leave the river Strymon for the Ister, where they rear their young. They depart in great crowds, and those that are before wait for those behind, for in flying over the mountains those behind cannot see the leaders. 3. The fish also, in the same manner, migrate either from or to the Pontus, and in winter they leave the deep water for the sake of the warmth of the shore, and in summer they escape from the heat by migrating from the shore into deep water. Delicate birds, also, in winter and frosty weather, descend from the mountains to the plains, for the sake of the warmth; and in summer they return again to the mountains for fear of the heat. 4. Those that are the most delicate are the first to make the change at each extreme of heat and cold, such as the mackerel migrate sooner than the tunnies, and the quails than cranes; for some migrate in August, others in September. They are always fatter when they migrate from cold countries, than when they leave warm countries, as the quail is more fat in the autumn than the spring: and so it happens that they migrate alike from cold countries and from warm seasons. Their sexual desires are also more violent in the spring, and when they leave warm countries.