BOZEMAN, Mont. (AP) — State wildlife authorities in southern Montana are seeking information after multiple trumpeter swans were shot dead at a pond near Bozeman last month.

Biologists and wardens from the state Department of Fish, Wildlife and Parks determined the swans were shot illegally, the Bozeman Daily Chronicle reported Monday.

Experts collected the dead swans for examination after receiving a report of the birds between the towns of Belgrade and Manhattan, department spokesman Morgan Jacobson said. The cause of death was not immediately known, but poaching was a possibility.

The Daily Chronicle previously reported seven swans were found dead, but the agency said it could not give a final count for how many swans had died until all analysis had been completed.

X-rays determined the swans were shot, and further analysis is pending.

Anyone who may have heard gunshots in the area is encouraged to report any information.

An investigation is ongoing.

Trumpeter swans are the largest waterfowl in North America and are protected by state and federal laws for migratory birds. The birds can be up to 5 feet (1.5 meters) in length, have a wingspan up to about 7 feet (2 meters) and weigh over 20 pounds (9 kilograms).