An appeals court in San Francisco has upheld a plan by wildlife officials to kill barred owls to assess their effect on the threatened northern spotted owl.

The 9th US Circuit Court of Appeals said on Wednesday that the experiment by the US Fish and Wildlife Service did not violate a federal law aimed at protecting migratory birds.

Experiment: the barred owl. Credit:DON RYAN

The court said that law did not prevent killing one species to advance the scientific understanding of another.

The ruling came in a lawsuit filed by advocacy groups Friends of Animals and Predator Defence challenging the agency's plan.