Photo: Yellowstone National Park

WYOMING — It’s calving season for Bison in the Greater Yellowstone Ecosystem, with new calves increasing herd sizes in Yellowstone and Grand Teton National Parks.

According to Yellowstone National Park, baby calves are born in late April and early May with reddish-brown coats. They are nicknamed “red dogs” for their coat color but will turn dark brown by the end of the summer.

Born weighing about 30-70 pounds at birth, the calves can keep up with the herd two to three hours after birth. They are well protected by their mothers and other members of the herd and stay with their mothers for the first year of their lives.

A nursery group of bison cows and calves makes its way through Lamar Valley. Photo: Neal Herbert // NPS

Wolves and grizzly bears are bisons’ only predator. Bison calves are especially vulnerable, but by adulthood they can run up to 35 miles per hour.

Male bison can weigh up to 2,000 pounds and be up to six feet tall while females can reach up to 1,000 pounds and four or five feet in height. Bison are the largest mammal in North America.

With a life expectancy of about 15-20 years female bison, called cows, have one calf per year and only mate during the rut season which lasts from July to August each year. The gestation period is about nine to nine and a half months.

An estimated 30 to 60 million bison may have roamed North America before the mid-1800s. Bison herds once ranged across the entire continent, from the plains of Mexico to the Appalachian mountains, but the majority lived on the Great Plains.

With the arrival of European settlers and their expansion west during the 1800s, the bison population was extremely affected. Sport hunting, loss of habitat, and a particularly brutal campaign by the U.S Army, targeting native plains tribes, nearly eradicated bison in North America.

In the 1970s, there were less than 500 animals left.

According to Yellowstone National Park, the bison population in Yellowstone fluctuates from 2,300 to 5,500 animals in two subpopulations, defined by where they gather for breeding. The northern herd breeds in the Lamar Valley and on the high plateaus around it. The central herd breeds in Hayden Valley.

“Due to high rates of survival and reproduction, the bison population increases by 10 to 17% every year: ten times faster than the human population grows worldwide,” says Yellowstone National Park.

Lindsay Vallen is a Community News Reporter covering a little bit of everything; with an interest in politics, wildlife, and amplifying community voices. Originally from the east coast, Lindsay has called Wilson, Wyoming home since 2017. In her free time, she enjoys snowboarding, hiking, cooking, and completing the Jackson Hole Daily crosswords.