BILLINGS, Mont. (AP) — Wildlife officials say the annual count of a major elk herd that migrates between Yellowstone National Park and Montana was unable to be completed this year.

But scientists from the park and the Montana Department of Fish, Wildlife and Parks say a related study suggests the population size remains similar to the 3,915 elk counted in 2013.

Officials said Monday that weather problems prevented completion of the Northern Yellowstone Elk Herd survey when it was attempted in February.

The herd peaked at about 20,000 animals in 1992. That was just a few years before gray wolves were reintroduced to the Yellowstone area from Canada after being absent from the region for decades.

Also taking a toll on elk have been hunters, other predators including bears and harsh winters.