(CNN) - Baby bison are big eaters. The year's first newborn buffalo at Custer State Park in South Dakota has packed on close to 20 pounds in her first two weeks.
The March 22 arrival is actually an American bison, which is the correct species name, but "buffalo" is frequently used interchangeably.
"So technically they are bison. The term 'buffalo' is used just because most people know exactly what you're talking about when you use the term 'buffalo,'" says Mark Hendrix, resource program manager at Custer State Park.
This year's first calf is a female, or heifer, and she's one of about 450 calves expected in the park this spring.
"They calve out on their own throughout the park, scattered wherever they want. So a lot of them will kind of wander off into the trees, have their calves and then they'll come back to the herd a day or two later," says Hendrix.
The park doesn't name the calves -- it's hard to keep track of hundreds of newcomers -- but park visitors have been calling the premier heifer "Helmsley" after the Helmsley Charitable Trust.
She was born on the same day that the park received a $1.8 million dollar grant from the trust for fire rehabilitation, according to Kobee Stalder, the park's visitor services program manager.
The calves usually start arriving toward the beginning of April, and so far about a half dozen have been born. The herd will number about 1,300 with all the new arrivals.
Calves usually weigh between 35 and 50 pounds at birth. The first heifer of 2018 will probably weigh about 400 pounds by fall, Hendrix says, and she will likely grow to be a 1,000- to 1,100-pound cow.
Custer State Park, which encompasses 71,000 acres in South Dakota's Black Hills, is also home to the world's longest-running bison auction. Between 300 and 400 head of surplus bison will be sold at the 53rd annual auction in 2018.
The park's herd is state-managed for conservation, but the bison are available for sale to private producers. The sale generates a significant amount of the park's revenue, which is used to support the state park system.
The surplus animals often go toward growing the bison herd, Hendrix says. "There used to be millions of bison in the United States. Currently, there's about 400,000 bison and [the industry] goal is to try to push to get one million bison back in North America."
Driving the 18-mile Wildlife Loop Road is a great way to encounter Custer State Park's herd. Guests may also spot white-tailed deer, mule deer, elk, bighorn sheep, coyotes, prairie dogs and more.
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