The September 2014 edition of Equus magazine summarizes the recent research of Dr. Konstanze Krueger of the University of Regensburg who investigated the "lead mare" theory. She and her students watched three herds of feral horses in the mountains of Italy to determine driving behavior (moving other horses from behind) and departures (one member leaving and the herd following). Horses were between 1 and 23 in age. Two of the herds had one alpha stallion and the third harem had one alpha stallion and two lower ranking bachelors. Each of the alpha stallions had been with their herds for years.
Only stallions exhibited driving behavior. Interestingly, mares of all ranks were observed in moving the herd by departing from it with higher ranking mares exhibiting more departures. As Dr. Krueger states, "But the theory of 'individual lead mare' roles is not true. There is no particular lead mare in a group. Higher ranking mares lead more altogether; but which one of the mares takes the lead depends on the situation." Leadership is shared within a herd whereas hierarchy is relatively stable. She cautions that "...being a 'boss' does not necessarily mean that you become a leader your horse would choose to follow."