JACKSON, Wyo. (AP) — Biologists say forage conditions at the National Elk Refuge have slipped to the point that they have to begin supplemental feeding of elk and bison this winter.

The winter feeding program is set to being on Tuesday. Officials say there are about 6,000 elk and about 600 currently wintering on the refuge.

Refuge managers try to keep supplemental feeding to a minimum to reduce the time bison and elk are concentrated on the feed lines to reduce the potential for disease transmission.