YELLOWSTONE NATIONAL PARK (AP) — A bison expert says Yellowstone's buffalo population could break a record this fall even though it faces continuing challenges.

The record of 4,002 animals dates to 1994. ‘‘We'll probably just barely top that this year,'' said Rick Wallen, of Yellowstone's Bison Ecology and Management Center.

Between 600 and 700 bison calves were born in the park this spring.

The park's population continues to grow despite Montana livestock officials' policy of slaughtering bison that leave the park out of concern that they could spread brucellosis to cattle.

The disease can cause cattle to abort and, in rare cases, causes undulant fever in humans. Officials try to prevent transmission to cattle by keeping bison and cattle separate.

Bison were hunted nearly to extinction in the early 1900s.

Around that time, a man nicknamed Buffalo Jones lobbied Congress to restore the park's bison herd. He rounded up 25 bison and became the park's first bison caretaker. The herd grew to 1,200 in just 30 years.

The park's bison management plan calls for a population of 3,000. When the population falls below that number, bison that leave Yellowstone are captured and tested for brucellosis; those that test positive are killed.

Bison are killed without testing when the herd exceeds 3,000.

About half the bison tested currently test positive for brucellosis antibodies, and about half of those are believed to be infected.