Government wildlife authorities and some conservation groups have for years argued that allowing some legal hunting can help reduce the illegal killing of threatened carnivores like wolves and grizzly bears.

Their theory — though there has been little scientific research to support it — has been that legalizing hunting helps reduce resentment among landowners, increase support for conservation and decrease poaching.

But the authors of a new study of wolves, published Wednesday, say their findings offer the first quantitative evidence that government authorization of any legal killing of wolves appears to increase illegal killing.

The study looked at wolves in Wisconsin and Michigan, states where the animals have at different times been placed under federal protection, removed from the endangered species list or relisted after court challenges.