CHADRON, Neb. (AP) — Pregnant bighorn sheep ewes have been fitted with special transmitters in an effort to improve the health of wild herds in northwest Nebraska.

The Nebraska Game and Parks Commission says a helicopter was used to help in the capture of 20 this week. They were fitted with monitors in their reproductive tracts. The monitors are expelled when the lambs are born, alerting commission staffers who will race to the area.

Their goal is to find and fit each lamb with a tracking collar to help biologists learn what’s causing so many of the lambs to die in the Pine Ridge area of Dawes and Sioux counties. The commission says the experts think no lambs survived last year and that most died within a couple months of birth.