Wolves preying on livestock in western Wyoming have learned what aircraft sound like and are eluding wildlife officials who are working to eliminate the problem pack.

The Jackson Hole News and Guide reports the Dell Creek Pack of 16 wolves stands at 11 due to aerial gunning.

Wildlife official Mike Jimenez says the pack is responsible for maybe 10 livestock depredations.

He said wolves that have been darted before will go for the trees as soon as there is a helicopter in the sky.

Jimenez said officials will probably stick with aerial gunning, but that trapping or ground-based calling and shooting are other options.

The U.S. Department of Agriculture's Wildlife Services is killing the wolves on behalf of the U.S. Fish and Wildlife Service.