Karen Sussman, president of the International Society for the Protection of Mustangs and Burros, based in Lantry, South Dakota, works to preserve the genetically pure and rare herd of wild horses from Gila Bend, Arizona.
They are descended from horses brought to America in the 1600s by Father Eusebio Kino, a missionary from Spain. The original horses survived a trip across the Atlantic in small sailing vessels and a 1920s campaign of capture and shipment to slaughter.
Sussman's story is featured in a new book, Horses with a Mission: Extraordinary True Stories of Equine Service, by Allen and Linda Anderson.
In her story in the book, Sussman discusses wild horses based on research into four herds she has rescued that are now free to roam and behave naturally.
She claims that when the Bureau of Land Management does roundups, they disrupt the harem system that has been in place for more than 500 years. The wild horses never band up the same way again.
Without supervision from the wiser stallions that have been removed and that typically maintain harmony in the herds, the younger stallions take charge.
"It's analogous to having fifth graders running the neighborhood," Sussman says.
The young stallions breed with fillies, and the fertility rates skyrocket.
"The increasing fertility rate of the herds is the direct result of harem bands being destroyed as stallions are separated from their mares when captured in roundups," Sussman says.
She cited the example of one herd with a lead mare named Diana, that has been kept intact in conditions that are natural to wild horses.
"The herd has been able to teach us the importance of keeping harems together and of allowing the wild horses to maintain strong social bonds."
One of Sussman's goals is to bring the conservation model she is developing to other areas of the United States and to develop ecotourism nationally and worldwide.
Sussman described the Bureau of Land Management's methods as disruptive - "chasing terrified horses with hovering helicopters". She said the methods used in South Dakota are based on the natural harmony of wild horse herds and harems.
Sussman explained that Diana roamed the desert areas and public lands near Gila Bend where the last of her herd remained.
The Gila herd was eventually given legal protection, thanks to the efforts of the International Society for the Protection of Mustangs and Burros' first president, Velma Johnson, known as Wild Horse Annie.
In 1999, when the bureau threatened to remove the Gila herd at the request of ranchers, Sussman stepped in. Eventually she brought Diana and her herd to a ranch four hours north of the Badlands, on the Cheyenne River Sioux Reservation, in Lantry, South Dakota.
The Andersons, who wrote the book, said: "Karen and Diana's story is a wakeup call that wild horses help us to remember our country's history that was built on the backs of horses, to cherish beauty for beauty's sake alone, and to preserve the type of freedom we all aspire to attain."
Joe Camp, author of "The Soul of the Horse" and creator of the films starring the canine superstar Benji, said: "Karen Sussman's account of rescuing and documenting a wild horse herd reminds all of us that native and indigenous horses have been here for 52 million years."
Horses with a Mission: Extraordinary True Stories of Equine Service
By Allen and Linda Anderson, ISBN: 978-1-57731-648-0
Available in bookstores nationwide and online.