THE MIGRATIONS OF MAMMALS. 247 



struggle does the new candidate for leadership gain his troop of 

 mares; the old leader does not readily relinquish his rights. For 

 hours together the stallion stands on the top of a hill or on the 

 shoulder of a ridge, keenly scanning the country around. His eye 

 wanders over the desert, his dilated nostrils are turned towards the 

 wind, his ears are directed forwards on the alert. Eager for battle, 

 he rushes at full gallop towards every herd which approaches, every 

 adversary who shows himself; and a furious struggle takes place for 

 the possession of the mares, who always attach themselves to the 

 victor. Such combats and strife set the herd in motion, detach it 

 from the place where the summer has been spent, and lead on to 

 migrations which become gradually regular, prolonged, persistent, 

 and almost uninterrupted. In the course of these, if not before 

 the end of the combats just described, the kulan troops assemble 

 in ever-growing numbers, until at length herds of more than a 

 thousand head set out together for fields which give promise of 

 pasturage. They do not break up while in their winter quarters, 

 and they are thus compelled to be continually on the move in order 

 to find sufficient nourishment. The combined tread of the army, as 

 they gallop on in their usual furious fashion, rings dully out, and 

 more than once, in Russia, the sound has called the Cossacks of the 

 military cordon to arms. No wolf ventures to attack such a herd, 

 for the courageous wild horses know so well how to use their hoofs 

 against him that he soon gives up any attempt; it is only the sick 

 and exhausted horses which become his prey, as he follows the 

 wandering herd. Even man can do them no great damage, for their 

 caution and shyness render them difficult of approach. But winter, 

 especially if much snow falls, brings them much suffering. The 

 pasture, at all times scanty, is exhausted the more quickly the more 

 numerous the herd which feeds on it. Then the animals devour indis- 

 criminately all the vegetable substances they can find. For months 

 together they have to maintain life on leafless shoots. Their bodies 

 cease to be fat and plump, till at length they are like wandering 

 skeletons. The mother, herself starving, is no longer able to nourish 

 her foal, for the milk-yielding udder dries up in times of such need. 

 Many a one whose tender youth is unable to endure the hard fare 



