The public's help is sought for information about the killing of more than a dozen swans in mid-December in Stevens County, in west-central Minnesota.

Without giving more details about the location or the type of swans, the U.S. Fish and Wildlife Service (USFWS) said in a news release that the deaths happened between Dec. 16 and 17.

Common to Minnesota, trumpeter and tundra swans are protected by state and federal law.

Minnesota has the highest population of trumpeter swans in the lower 48 states.

A USFWS and Department of Natural Resources survey last May estimated 39,000 breeding adults, said Lori Naumann, a specialist in the DNR's Nongame Wildlife Program. Based on the survey, it is estimated that there are 65,000 trumpeter adults.

While some head to the central U.S., trumpeter swans tend to overwinter in central and southern Minnesota where there is open water and food. Trumpeters were hunted to extinction by the late 19th century in Minnesota. Government agencies like the Nongame Wildlife Program, in partnership with public groups, restored the swan population.

Tundras are the most common swan in North America and congregate in vast numbers on the upper Mississippi River in mid-winter en route to their winter grounds in Chesapeake Bay on the East Coast.

"We are responsible for protecting America's wildlife from poaching, illegal commercialization and other kinds of wildlife crime," the USFWS said in a news release, referring to the Migratory Bird Treaty Act of 1918, which protects almost all native U.S. birds, including swans.

Anyone with information is urged to contact USFWS agent Andrew Daiber at andrew_daiber@fws.gov.