BILLINGS, Mont. (AP) — Dozens of wild mustangs from the Pryor Mountain Wild Horse Range along the Montana-Wyoming border are slated to be removed this year to reduce the size of the famous herd.

The federal Bureau of Land Management on Wednesday announced approval of a roundup that would reduce the 170-horse herd to 120 or fewer animals.

The agency says the roundup is needed to keep the horses from overgrazing their 38,000-acre range — the nation's first wild horse preserve.

The horses in the Pryors are said to be descendants of animals brought to the New World centuries ago by Spanish conquistadors.

Some horse advocates had pushed for greater use of fertility control drugs as an alternative to roundups.

Wednesday's decision is subject to a 30-day appeal period ending May 3.