Sitting motionless on a fallen tree trunk, Rada Surmach strained to hear the mournful echo of nesting owls, deep in the Tunsha River Valley of the Russian Far East.

In the twilight, she finally heard it: The duet of the Blakiston’s fish owl, an endangered species whose six-foot wingspan makes it the world’s biggest owl.

These haunting duets, rare among owl species, reinforce pair bonds. It’s as if the male is calling out to his mate, “I’m here!” to which the female responds in a lower tone, “I’m here too!”

Perched high in the forest canopy, fish owl pairs perform a four-note duet of synchronized calls that can last up to two hours. These raptors, known for their intense yellow eyes and showy