Fish Link: A Duet of Fish Owls - Scientific American

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After weeks of delays, I’d finally reached the wild. I was in the Samarga River basin, a mountainous, roadless corner of the Russian Far East inhabited by indigenous Udege hunters, Amur tigers and—most importantly for me—Blakiston’s fish owls. These were the largest owls in the world; endangered giants that hunt for salmon in rivers and nest in enormous trees. Joined by Sergey Avdeyuk, an experienced woodsman, I was dipping my toe into my first year of fish owl fieldwork, the first of many. We were here to find fish owls to better understand their habitat needs so we could develop a conservation plan to protect them.

There were no roads here, so Sergey and I drove a snowmobile along the frozen river south of the small Udege village where we were based, and spent an afternoon searching the forest there for signs of fish owls. We found nothing, and paused an hour or so before dusk to drink hot tea from a thermos and chart our next steps. Sergey wanted to survey for owls calling downstream, from the far side of the river valley, so that we could listen from two places at once and maximize our survey coverage. He would leave me here, drive the snowmobile along the river another two to three kilometers south, then collect me on the way back to town. The sound of his receding machine carried far in the clear winter air, and I could hear the high whir of its engine long after it was out of sight.

A light wind moved through the treetops, rattling the bare canopies of aspen, birch, elm and poplar and occasionally gathering strength and dropping to gust brashly just above the frozen river. I listened under the sound of the wind for the distinctive call of the fish owl. Fish owls hoot at frequencies in the low-200-hertz range, in the same ballpark as a great gray owl and twice as low as a great horned owl. In fact, the frequency is so low that the sound can be difficult to capture well with a microphone.

On the tapes I’d later make, the owls always sounded far away, muffled, lost, even if they were close by. The low frequency of the vocalizations served a purpose: it ensured that sound passed cleanly through dense forest and could be heard some distance away, up to several kilometers. This was especially true in winter and early spring, when there was little tree cover and the crisp air facilitated movement of sound waves.

Fish owl pairs vocalize in duets. This is an uncommon attribute recognized in less than 4 percent of bird species globally, most of which are in the tropics. The male usually initiates a fish owl duet, filling an air sac in his throat until it’s swollen like some monstrous, feathered bullfrog. He holds that position, the white patch of his throat now a conspicuous orb contrasting against the browns of his body and the grays of the gathering dusk, a signal to his mate that the vocalization is impending. After a moment he exhales a short and wheezy hoot—the sound of someone having the breath knocked out of him—and she answers immediately with one of her own, but deeper in tone. This is unusual among owl species, where females usually have the higher voice. The male then pushes out a longer, slightly higher hoot, which the female also responds to. This four-note call-and-response is over in three seconds, and they repeat the duet at regular intervals for anywhere from one minute to two hours. It is so synchronized that many people, hearing a fish owl pair vocalize, assume it is one bird.

Blakiston's fish owl. Credit: Jonathan C. Slaght

The duet is both a territorial call and a pair bond affirmation. The frequency of duets follows an annual cycle, with the most active vocalizations occurring in February during the breeding period. Duet bouts can be long during this time, lasting for hours, and can be heard throughout the night. Once a female is incubating eggs, however, in March, these calls are most often heard only at dusk, perhaps because the birds are reluctant to advertise their nest location. Duets increase again as their young hatch and fledge but, by summer, begin to diminish in frequency again until the next breeding season.

I had some concern that the strengthening wind might cut through my insulation as I waited, still and exposed. I spotted a massive log half-buried in snow about a hundred meters away, a large tree that had been uprooted in some storm and carried there by flood. I used my feet to dig out and pound down a shallow depression in the snow by the tree’s base and crouched there to take shelter from the wind, largely concealed by roots and shadow.

About a half hour later, focused on the joy and crunch of some hard candies I’d found in my pocket, I did not hear the roe deer approaching. It burst into view not more than 50 meters off, finding purchase on the hard crust of river ice and bounding upriver, a hunting dog at its heels. The gasping deer approached a section of deep, open river, about three meters wide and 15 meters long, and without pausing plowed into the water. Perhaps it had intended to jump clear across but too late realized it lacked the strength to do so. The dog stopped short and bayed with exposed teeth. I was frozen in place. From my low vantage point among the roots, I could see only the deer’s head—snout held high and nostrils flared—bobbing above the clean line of the river surface.

The deer pushed briefly against the flow and then succumbed to it, drifting like a rudderless boat, then disappearing from view at the downstream lip of ice. I stood up for a better view and saw only the open wound of quiet, rushing water. I envisioned the deer in the darkness beneath the ice, water likely filling its lungs, a victim of the Samarga floating serenely seaward, the winter and village dogs now irrelevant. The dog noticed my movement and pivoted toward me with ears erect and a quivering, questioning muzzle. It dismissed me as an unknown human, then refocused its attention on the exposed river, sniffing at it before trotting back downstream.

I returned to my tree hole, stunned by the quiet violence of this place. Primeval dichotomies still outlined existence on the Samarga: hungry or satiated, frozen or flowing, living or dead. A slight deviation could tip the scales from one state of being to the other. A villager might drown because he went fishing in the wrong spot. A deer evaded capture by a predator only to find death anyway because of a misstep. The line between life and death here could be measured in the thickness of river ice.

A muted tremor in the air pulled me from my thoughts. I sat up and took off my hat to expose my ears. After a protracted silence I heard the sound again: a distant, muffled tremor. But was it a fish owl? It must have been quite far across the river valley, and I could really hear only one note, maybe two, not the four I was expecting. I had a sense of what a fish owl sounded like only from Sergey’s coarse mimicries, and it was hard to evaluate the quality of their hoots without the real thing to compare it with. What I was hearing now didn’t really match. Perhaps this was just a single fish owl—not a pair? Or maybe a Eurasian eagle owl? But those owls had higher voices than what I was hearing and did not duet. The sound repeated every few minutes or so, until the gradual, almost imperceptible transition from day to night was complete. In the dark, the vocalizations ceased.

An undulating, high-pitched whine from downriver told me that Sergey was returning, and I soon saw the snowmobile’s single headlight casting its pale beam on the snow. “Well?” he said triumphantly as I came out to meet him. “Did you hear them?” I told him that I thought so, but maybe only one bird. He shook his head. “There were two—it was a duet! The female call is even lower than the male’s and harder to hear, so maybe you missed it.”

Sergey possessed a highly perceptive sense of hearing—he could confidently discriminate far-off duets when all I could make out was the breathy higher voice of the male. Later, even when I was sure there was just one bird, we would sneak closer, and only then could I make out the female as well. Fish owls are non-migratory, enduring the summer heat and winter frosts in the same places, so if we heard a duet, that meant the pair was resident to that patch of forest. These were long-lived birds—there are records of wild fish owls more than 25 years old—so duetting owls were likely to be in the same place year in and year out. If we heard just one bird hooting, however, that might mean it was a bachelor owl looking for a territory or a mate. If we heard one today, it did not mean it would be there tomorrow, much less the next few years. We needed resident pairs for our study population: birds we could track over a long period.

I told Sergey about the deer and the dog. He spat and shook his head incredulously. “I passed that animal! I met its owner fishing downriver. He said his team of dogs had killed five roe deer and three red deer today alone! He complained that rich city folk have been flying into the region all winter and shooting the deer; that’s why the woods were empty. Meanwhile, his unattended dog was drowning one!”

We rode back to the village in darkness and silence.

This is the 18th post in an ongoing series, “East of Siberia.” It is adapted from Owls of The Eastern Ice, (Farrar, Straus, and Giroux), which reached the 2020 National Book Award for Nonfiction longlist, and which was named a New York Times Notable Book for 2020. Follow the author on Twitter @JonathanSlaght.

East of Siberia: Owls and the Meaning of April

East of Siberia: Goral on the Cliffs

East of Siberia: Heeding the Sign

East of Siberia: A Spoon-Billed Curiosity

East of Siberia: The Fragility of Field Plans

East of Siberia: An Undesirable Nest

East of Siberia: Shadows of Wolves

East of Siberia: A Long Walk Through Leopard Country

East of Siberia: A Tiger Conservationist in the Urban Jungle

East of Siberia: By Chance, Food and Shelter

East of Siberia: Arsenyev in the Land

East of Siberia: Tigers and the Art of Persuasion