BILLINGS, Mont. (AP) — Authorities have launched an investigation after 15 horses were found dead in a pasture on the Fort Peck Indian Reservation.

The Billings Gazette reports the horses were found north of Wolf Point last week and appear to have been dead for about five days before a resident alerted tribal wildlife officials.

Fort Peck Department of Fish and Game Director Robert Magnan says the horses may have died from dehydration. About 10 of the horses were found near a dried-up water source. The other carcasses were scattered around the pasture.

Magnan says the tribe and the Roosevelt County Sheriff's Office are working with the state Department of Livestock to identify the horses' owners.

The investigation could result in animal cruelty charges.