The sound, when Mischa makes it, lasts about three and a half seconds. It begins with a soft metallic creak, rises in pitch, pauses, and ends with a small wooden thump. To a person who has spent any time in the long, low building at the Haidlhof Research Station outside Vienna, it is immediately recognizable.

It is the sound of one of the aviary's exterior windows being slid open.

Mischa is an eight-year-old female common raven, Corvus corax, hand-raised at Haidlhof since she was a chick. She has been part of the station's long-term study of corvid cognition since 2018. She is, by the standards of a species famous for intelligence, neither the brightest nor the most social bird in her group.

She is, however, the only one who has begun mimicking the window.

The first recording was made on the morning of May 14 by a doctoral student named Felicia Brandt, who had set up an audio recorder in the aviary for an unrelated study on contact calls. Brandt was reviewing the files that evening when she heard, between two long stretches of normal raven vocalization, a sound she initially mistook for a maintenance worker.

The maintenance log showed no one had entered the aviary that morning.

Brandt played the recording for Dr. Thomas Bugnyar, who has run the Haidlhof corvid program for two decades and is one of Europe's most respected raven researchers. Bugnyar listened to the clip twice.

"He laughed," Brandt said. "And then he said, that is Mischa."

What makes the Haidlhof case interesting is not the mimicry itself but what Mischa appears to be doing with it.

Common ravens are accomplished vocal mimics. They are capable of reproducing human speech, the calls of other bird species, and a wide range of mechanical sounds. In captive settings, individual birds have been documented imitating doorbells, telephones, dripping taps, and, in at least one published case, a chainsaw.

What makes the Haidlhof case interesting is not the mimicry itself but what Mischa appears to be doing with it.

The aviary's exterior windows are slid open every morning at approximately seven-thirty by a keeper named Stefan Hoch, who does so to refresh the air and to scatter the morning food. The ravens have, over years, learned that the sound is followed by food.

Beginning in the second week of May, Mischa began producing the window sound in the late morning, after the actual window had been opened and closed. She produced it most often when Hoch was visible through the interior glass but had not yet entered the aviary.

The other ravens, who can also recognize the sound, came to the feeding area when she made it.

Hoch, who arrived a few minutes later carrying no food, found them already gathered.

"She fooled them," Bugnyar said. "That is what we are looking at. She used a sound that her flockmates associate with food, in a context where she knew food was not coming, and she got them to gather. We do not yet know whether she did it on purpose. We are designing experiments to find out."

Bugnyar is careful with the word purpose. The literature on intentional deception in non-human animals is contested. Corvids, along with great apes, are among the few species in which experimental evidence for so-called tactical deception has been documented, but each case is subject to alternative explanations.

The Haidlhof team is now designing a series of trials in which Mischa will be observed in the presence of various combinations of other ravens, with and without visual access to the human keepers. The question is whether her use of the mimicked sound varies systematically with social context.

The results, Bugnyar said, will take months to collect and longer to publish.

In the meantime, Mischa continues. She produces the window sound several times a day. The other ravens have, over the past two weeks, begun to ignore it. They come to the feeding area when Hoch's actual footsteps are audible on the gravel outside, not before.

Whether Mischa will develop a new sound to replace the one her flockmates have learned to discount is, in Bugnyar's view, the more interesting question.

"She has learned that a sound can move other birds," he said. "That is a useful thing for a raven to know."

Mischa, on the afternoon Brandt was interviewed, was perched on a high branch near the south wall of the aviary, preening her primaries. She made no sound at all for nearly twenty minutes. Then, without looking down, she produced a small, precise metallic creak.

No window had opened. No keeper was visible.

She preened another feather and was quiet.