SALEM, Ore. (AP) - The number of wolves in the wilds of Oregon increased slightly last year, according to state wildlife officials. But they lost track of the South Snake Pack because none of its members wears GPS collars.

Furthermore, four of the 11 tracking collars that were placed on other wolves last year failed within six months.

In its draft wolf report covering 2016, the Oregon Department of Fish and Wildlife described the challenges of monitoring the state's growing wolf population. The species returned to Oregon in 1999 when one wolf that had been re-introduced into Idaho walked across the state line.

The draft report released Tuesday says the minimum known wolf population in 2016 was 112, a 2 percent increase from 2015.