Oscar Colegrove, a field technician with the Hoopa Valley Tribe and a tribal member, fixes an Audio Recording Unit (ARU) in suspected northern spotted owl habitat. Spotted owls have been observed nesting here in previous years, and the ARU is a passive way to survey for the presence of owls. They operate much like an acoustic version of a camera trap. When an animal calls, the unit activates and records. Later a computer program helps to identify spotted owl calls. While these units are helpful in conducting surveys, they cannot replace the information gleaned from direct observation.