Bison profile, Yellowstone National Park/Neal Herbert, NPS

Work began this week to reduce the number of bison in Yellowstone National Park's herds, though whether the target reduction of 600-900 animals will be attained is hard to predict.

Until February, winter was relatively mild in the park, and so there was no great push of animals to lower elevations in the Gardiner Basin of Montana just north of Yellowstone's boundary. On Wednesday the park culling operation began, with 23 animals captured and about 500 more north of Mammoth Hot Springs, according to park staff.

Each fall the Interagency Bison Management Plan, which is based on input from tribes, federal officials, and Montana officials, sets a rough number for reducing the park's herd. Late last summer the bison population was estimated at 4,500 animals, and in November the IBMP partners settled on the 600-900 reduction, explained Tim Reid, the park's bison program manager.

Bison hunts in the Gardiner Basin, some conducted under treaty agreements with tribes and others through the Montana Fish, Game and Parks Department license sales, contribute towards that reduction cull. How many bison are corraled by park staff for shipment to tribes, slaughter, or even release back into the park depends on how many are taken through the hunts.

The late movement of bison out of the park could result in a low cull, explained Reid, as the park's capture operations typically wrap up by the end of March so as not to involve any cows in late-term pregnancies.

"We’re not going to take aggressive management action to ensure we need that (600-900) number. It’s a desired target range. Whether or not it happens is beyond our control," he said during a phone call last week. "Our snowpack has definitely caught up, but there are quite a few points of light that have to align in order to have a big push. Whether or not that aligns with our kind of operational window, it’s all kind of up to Mother Nature, and she typically bats last."