RARE SPECIES: Sixty-two Przewalski's horses raised in the Gansu Research Center for Endangered Species endured the winter of 2010 successfully (XINHUA)

Seven wild horses raised in captivity were released into the West Lake National Nature Reserve in Dunhuang, northwest China's Gansu Province, on September 25, 2010. They were the second batch set free by Chinese scientists over the past decade, aiming to help them "return home."

"Situated some 180 km west of Dunhuang, the nature reserve, covering an area of 6,600 square km, was the habitat of wild horses more than 2,000 years ago," said Sun Zhicheng, a local wildlife management official.

"In the vast nature reserve, patches of wetlands function as fences, creating favorable conditions for tending and protecting these horses that prefer a dry grassland environment," said Hu Defu, a zoologist from Beijing Forestry University.

Beginning in 1989, the Gansu Research Center for Endangered Species introduced 18 Przewalski horses from zoos in Beijing, San Diego and Munich. After 20 years of captive breeding, the center eventually built a herd of 70, paving the way for last year's trial release.

Przewalski's horse (Equus ferus przewalskii) is a rare and highly endangered subspecies of wild horse (Equus ferus), native to the steppes of Central Asia, specifically northwest China's Gansu Province, Xinjiang Uygur Autonomous Region and Inner Mongolia Autonomous Region, as well as the Republic of Mongolia. The lineal offspring of dawn horse (Hyracotherium eohippus) and the only true wild horse alive today, Przewalski's horse is distinguished from other subspecies by several unique genetic differences, such as 66 instead of the 64 chromosomes possessed by the domestic horse.

The horse itself is named after Nikolai Mikhaylovich Przhevalsky (1839-88), a Russian geographer, naturalist and explorer of Polish origin, who made four journeys to Central Asia during his lifetime. He found the horse in 1879 in the Junggar Basin of northern Xinjiang and made it known to the West two years later. From 1899 to 1903, some 50 Przewalski horses were transported to Europe and placed in zoos. A dozen of them reproduced and formed today's population.

As a result of excessive hunting, the wild population of Przewalski's horse declined sharply in the 20th century, becoming even fewer than panda. The last herd was sighted in 1967 and the last individual in 1969. The subspecies was then designated "extinct in the wild."

Currently, the captive population of Przewalski's horse is no more than 1,000 all over the world, already in the 10th or 11th generation. These horses generally gain a weight of 50 to 70 kg on average with thicker legs, but apparently losing the vigilance and excellent galloping ability characteristic of their wild ancestors.

The last appearance of Przewalski's horse in the wild in China was in 1966. In 1985, the country reintroduced 11 wild horses from overseas, and initiated a breeding program with the creation of a research center at the southern edge of Junggar Basin.

"The horses quickly adapted to their new environment, and grew to a herd of nearly 200 by the year 2000," said Cao Jie, then Director of Xinjiang Research Center for Wild Horse Breeding. Cao and his colleagues then made the first attempt in history to breed wild horses in the wild.

On August 28, 2001, a total of 27 wild horses were let loose into Kalamely Nature Reserve in the Junggar Basin. Kalamely is a mountainous area with plenty of water and lush grass, but it is also a haunt of wolves—a major enemy of wild horses.

The first step was extremely difficult, as the horses had been accustomed to human care. They were also threatened by various genetic diseases as a result of long-term inbreeding. In the beginning, Cao even made the rather pessimistic prediction no more than half of them would eventually survive.

While keeping a close eye on the herd, researchers systematically reduced artificial feeding, forcing the horses to look for suitable pastures by themselves and to recover their wild nature little by little. In April 2004, signals from tracking devices on the horses showed that they had split into three herds—a prerequisite for survival in the wild, said Hu. In August 2006, a female horse gave birth to its young, marking successful reproduction in the wild.

Thanks to the dedicated efforts of those researchers, the breeding rate and survival rate of these horses roaming wild have both reached more than 80 percent, the highest in the world, leading to the change of the rare animal's status from "extinct in the wild" to "endangered." In 2008, Przewalski's horse was reclassified after a reassessment as "critically endangered" on the Red List of Threatened Species of the International Union for Conservation of Nature.

Hu said there are several criteria for deciding whether or not the wild horses have really "returned home." They include: independently finding water and grass, naturally propagating themselves, successfully struggling for living resources with other species in the same area, and coping tactically with their natural enemies and severe natural calamities.

"The wild horses still need a dozen years to fully adapt to natural conditions," said Gu Jinghe, a zoologist from Xinjiang Institute of Ecology and Geography. "Only after a total population of at least 3,000 has been established and more herds are in existence, will they become the fittest to win their rivalry with other species."