JACKSON, Wyo. (AP) — The Wyoming Game and Fish Department has recorded 30 to 40 trumpeter swan deaths this winter in the northwest part of the state.

The final toll isn't yet in, but already more swans have died than in any winter since 2011-12, when 37 trumpeter carcasses were discovered.

Biologists are surprised by the high mortality rate because they expected fewer deaths during a winter that was mild at low elevations.

Game and Fish nongame biologist Susan Patla says as many as 10 swans struck power lines and died this winter.

Despite the high mortality, the total population of birds looked healthy this winter. Patla counted 1,061 statewide, which is the second-most ever, including 415 in the Jackson Hole area.