The disappearance of two tracked pine martens is being treated as suspicious, police said.
Cumbria Police and South Cumbria Pine Marten Recovery Project are appealing for information to help trace the rare animals that were released near Grizedale Forest earlier this year.
It is believed one of the mammals has two dependent kits.
Tracking them is part of a University of Cumbria-led scheme to reintroduce the species to south Cumbria and the loss “could compromise their recovery”, Cumbria Police said.