In other animals

there is no hair-growth at the pubes (for
some animals have no hair at all, and others have none on the belly,
or less on the belly than on the back), but still, in some animals the
change of voice is quite obvious; and in some animals other organs
give indication of the commencing secretion of the sperm and the onset
of generative capacity. As a general rule the female is
sharper-toned in voice than the male, and the young animal than the
elder; for, by the way, the stag has a much deeper-toned bay than
the hind. Moreover, the male cries chiefly at rutting time, and the
female under terror and alarm; and the cry of the female is short, and
that of the male prolonged. With dogs also, as they grow old, the tone
of the bark gets deeper.