I live near some tall eucalyptus trees in Southern California where many birds perch and sometimes nest, including hawks of several species as well as great-horned owls. This morning, before light, (Sept. 1, 2022), I listened for a time to the hoot of an owl. Then a second and unknown sound was heard. I set my recorder on the deck and captured these sounds. First are two calls from the unknown bird then two calls of the unknown bird answered by an owl. The CornellLab Merlin bird identifier app on my phone identifies the owl but does not recognize the unknown bird. I’ve heard the strange call before but never as answered by the owl. I and the Merlin app are stumped. Any suggestions? Many thanks to everyone. Jamulbob