A second group of wolves has been released in Colorado as part of a controversial, voter-driven initiative to reintroduce the predators to the state. Fifteen gray wolves from Canada were set free in the central mountains over three days last week,

Colorado wildlife officials released 15 wolves from Canada into the central mountains over the last week as part of the second wave of the state’s historic, voter-mandated reintroduction of the native predator.

The controversial effort to bring gray wolves back has had mixed success. Of the first 10 wolves brought in from Oregon, dubbed the Copper Creek pack, just six remain in the wild, with one having been recaptured and three killed, Coloradoan.com reported.

Officials with Colorado Parks and Wildlife announce they have completed the second year of the wolf release program by

Fifteen wolves from British Columbia were released from Jan. 12 to Jan. 16. CPW also rereleased five members of the Copper Creek pack that they captured last year.

The releases were done separately, the agency said in a press release Sunday, and all wolves were released into Eagle and Pitkin counties. The agency noted that this is the second of between three to five wolf release seasons.

Colorado Parks and Wildlife officials announced the release of 15 wolves into northern parts of the state, concluding their second year of wolf restoration efforts.