UGIINUUR, ARKHANGAI PROVINCE, MONGOLIA — The endless prairie has become a colander, peppered with what look like golf holes. Small gray rodents dart in and out, growing more numerous as late autumn sunshine warms the Mongolian steppe in the country’s central Khangai region.
Munkh-Erdene Baasanjav, a herder for 30 years, drills a hole into a raised mound and puts his hand inside to confirm his fears: a nest of thick grass. After removing the material, he pumps 60 liters of water into the hole, an environmentally friendly method of freezing the creatures out.
“When I was a child, there were rodents in some places, but now they are bustling everywhere like dust rising,” he says.
The pests are Brandt’s voles, one of the fastest reproducing mammals in the world. Female voles can give birth three times a year, up to 11 offspring each time. Just one of these rodents, smaller than a man’s hand, can eat 34 grams (1 ounce) of grass per day and stockpile 9 kilograms (20 pounds) of hay for winter.
Rising temperatures and overgrazing in Mongolia have fueled a dramatic increase in the vole population, by making soil conditions more favorable for nesting. The infestation threatens one-third of the country’s grasslands (38.6 million hectares, or 149,000 square miles), according to the Ministry of Food, Agriculture and Light Industry, leaving less food for livestock. The burrow holes also pose a hazard, leading horses and people to sprain their ankles or break bones. In response, herders and government rangers are working to reduce the vole population without harming other animals.
Enkhbold Nanj, a doctor of biological sciences at the Plant Protection Research Institute, a national organization that studies Mongolia’s grasslands and pests, says it’s normal to have 100 voles per hectare, but now some areas have up to 2,000. Estimates put their total population at over a billion.
“It’s too much,” he says. “It turns the soil over.”
Mongolia’s grasslands are state owned, while livestock are privately owned. A mainstay of the economy, the livestock sector accounts for more than 10% of the country’s gross domestic product and 23% of its labor force. Herders raise horses, cattle, sheep, goats and camels, and earn money by selling dairy products, meat and hides.
Since the country’s shift to a market economy, the number of livestock has nearly tripled, from 25 million in 1990 to nearly 70 million in 2020. The resulting overgrazing has caused soil deterioration on 78% of its grasslands, according to the Mongolian National Federation of Pasture User Group, a self-governing association of more than 80,000 members working to develop pasture management policies.
Dr. Tseveendorj Dalkhaa, head of the Rodent Research Laboratory at the Plant Protection Research Institute, says that humans must accept responsibility for disrupting the ecosystem by hunting or driving out the vole’s natural predators, such as foxes.
“If an animal exists in nature in a balanced way, it will not cause any harm,” he says. “But voles are said to be harmful when the right balance is lost.”
Odonchimeg Batsukh, GPJ Mongolia
The average temperature in Mongolia has risen more than 2 degrees Celsius (more than 3.5 degrees Fahrenheit) since 1939. When combined with overgrazing, the resulting dry, warm soil has created a favorable environment for voles to multiply, says Munkhnasan Tsevegmed, a pasture protection and restoration specialist at the Ministry of Food, Agriculture and Light Industry.
Before 2003, Enkhbold says Mongolians used pesticides to protect pastures, but these chemical methods have been discontinued due to their toxic environmental impacts.
Traditional extermination methods are far more labor-intensive. Since 2019, the government has provided a daily bonus of 2,000 Mongolian togrogs (70 cents) to herders and 20,000 togrogs ($7) to unemployed people who pour water into burrows, scatter rice contaminated with vole-killing bacteria and provide shelter for birds of prey.
These organized efforts have happened on 15% of the affected region so far, Munkhnasan says, which is not enough to overtake the vole’s reproductive success nor address the root causes of the infestation.
Enkhtur Badam-Ochir, a 41-year-old herder from Ugiinuur soum, or district, says that when she weighed a 1-year-old sheep to sell five years ago, it weighed 21 kilograms (46 pounds). Today, she says, the same sheep would not weigh more than 18 kilograms (40 pounds).
“The voles eat all the savory and nutritious grass,” Enkhtur says. “Therefore, animals do not fatten up.”
Odonchimeg Batsukh, GPJ Mongolia
Both local and national levels of government are focused on tackling the vole problem. While province governors adjust pasture usage plans by consulting local herders and considering annual plant yields, the Ministry of Food, Agriculture and Light Industry works to regulate land use and protection nationally. This includes a Law on Livestock Tax, effective July 2021, that uses revenue to fund more pest-control efforts and rehabilitate the country’s grasslands.
“The most affordable, effective and long-term measure to regulate excessive multiplication of voles is to reduce overgrazing and allow vegetation to regrow,” Munkhnasan says.
The number of livestock needs to reflect the size of the pasture, and the economic turnover of livestock should accelerate, he says. And herders should have fewer animals of better quality, rather than many animals of poor quality.
Although they recognize the problems of overgrazing, many Mongolians can’t afford to thin their herds.
“We supply all our needs with livestock, and the price of raw materials is not enough, so we don’t want to reduce the number of livestock,” says Munkhtsetseg Tudev, a resident of Ugiinuur soum. Any less livestock, she says, “is not enough to live on.”