Canadian wolves transferred to the United States in a repopulation experiment 13 years ago now have American lawyers howling.

The wolves originally from Alberta have returned as a top predator to the American wilderness from which they'd been hunted out.

But they've done so well they're now at the centre of two lawsuits.

One claims that they are still an endangered species and the other wants to declare open season on them.

However, U.S. Fish and Wildlife officials say they want Canadians to know that the wolves have prospered in Montana, Idaho and Wyoming.

The original 66 animals now number nearly 2,000.