The Secret Lives of Horses 3 of 5 Part article

Mares also sometimes have stallion preferences. They resist males they don't like with surprising persistence, even when that male has established himself as the band's stallion. Joel Berger of the University of Montana studied the behavior of two nonrelated mares that had spent several years together. The pair joined a band that was then taken over by a new stallion that asserted himself by attempting to copulate with them forcibly on numerous occasions. The mares refused his attentions and repeatedly aided one another by kicking and biting the stallion as he tried to mate, Berger observed in Wild Horses of the Great Basin. It's long been known that female elephants cooperate, but before ethologists began systematically studying free-roaming horses, few people suspected that cooperating mares were capable not only of waging such a fight—but of winning it. Given the truth about mares, “harem” seems like such an old-fashioned word.

Fending off unwanted suitors is not the only means by which mares rebel. For years Laura Lagos and Felipe Bárcena, both at the University of Santiago de Compostela in Spain, have been studying the behavior of Garranos, an unusual type of free-roaming horse. Garranos live rough, tough lives in the rugged hills of northwestern Spain and northern Portugal, where they are under constant threat from wolves. In the course of their work, Lagos and Bárcena catalogued the behavior of a pair of mares in one band that were strongly bonded with each other and that often stood just a bit apart from the rest of the band.

At breeding time, the mares went together to visit the stallion of another band. Lagos watched one of the mares consort with this stallion rather than with the stallion from her own band. Then the mares returned to their original group. When the second mare was ready to breed, the duo again deserted their original band and its stallion to consort with the other stallion. Then, again, they returned to their original group. This was not an anomaly. The mares did the same thing the following year. “They prefer their own territory, but the stallion of the other band,” she told me.

Adapted from The Horse: The Epic History of Our Noble Companion, by Wendy Williams