An experiment to see if killing invasive barred owls will help the threatened northern spotted owl reverse its decline toward extinction is underway in the forests of Northern California.

The U.S. Fish and Wildlife Service said Friday that specially trained biologists have shot 26 barred owls in a study area on the Hoopa Valley Indian Reservation northeast of Arcata, Calif.

They plan to remove as many as 118 barred owls from the area, keeping the 55 known barred owl nesting sites open over the next five years to see if spotted owls increase, said Fish and Wildlife Service biologist Robin Bown. Contractors go to an area that barred owls are known to be in, play a digital caller to attract them, and shoot the birds with a shotgun.

The service is spending $3.5 million over six years to remove 3,600 barred owls from sites in Oregon, Washington and California.

Barred owls migrated from the East in the 1950s and have become the single biggest threat to spotted owl survival.

Major cutbacks in logging in old growth forest that spotted owls prefer as habitat have not turned around their population decline, and scientists want to see if removing competition from the more aggressive barred owl will make a difference.

War on barred extends north

In British Columbia, the northern extent of the northern spotted owl's range, the provincial government approved the shooting of barred owls earlier in 2013. The provincial government had previously tried relocating the invasive owls but, with only an estimated 10 spotted owls remaining in the wild in southwestern B.C., a new policy authorizing the removal of barred owls within 5 kilometres of spotted owl territory went into effect in January.

Under the U.S. program, barred owl removal at research sites in Oregon and Washington state is set to begin next fall.

By then, the group Friends of Animals hopes to persuade a federal judge to issue a court order stopping the experiment in the U.S.

A lawsuit filed in U.S. District Court in Sacramento, Calif., argues the permits for killing barred owls issued under the Migratory Bird Act are invalid. The research does not benefit the barred owl, said Friends of Animals attorney Michael Harris.

It is not unusual to kill one species to help a threatened or endangered one: Cormorants and sea lions are regularly killed to help salmon.

Bown said blood and genetic samples are taken from each barred owl that is killed, and the frozen carcasses are sent to the California Academy of Sciences in San Francisco, where they are available for further research.

Among other things, scientists are checking the barred owls for toxins from prey contaminated with rat poison put out by illegal marijuana growers to protect their crops. Scientists hope to get a better picture of whether the rat poison is killing spotted owls, which eat similar prey. Scientists rarely get a dead spotted owl they can test for toxins.