Eulen spielen in Aberglaube und Folklore eine besondere Rolle. Sie gelten als Symbol der Weisheit, obwohl doch ausgerechnet über diese tagscheuen Vögel lange Zeit nur wenig Faktenwissen vorlag. Manchem mochten sie als schlechtes Omen erscheinen, wobei sie dank J. K. Rowlings „Harry Potter“-Reihe von einem enormen Sympathie-Schub profitieren, ist doch eine Schnee-Eule namens Hedwig die persönliche Botin des Zauberlehrlings. Leider ufert die Eulen-Begeisterung in Teilen Asiens so sehr aus, dass der illegale Handel mit den Vögeln in die Höhe schießt.
Jennifer Ackerman wollte es nicht beim Halbwissen belassen und hat sich mit der Biologie der Eulen und der aktuellen Forschung zu ihnen beschäftigt, Fachliteratur gelesen, Wissenschaftler interviewt, ihnen bei der Arbeit über die Schulter geschaut und sie oft wochenlang begleitet. Die Mehrzahl dieser Forscher ist in das „global owl project“ eingebunden, ein Konsortium von vierhundertfünfzig Spezialisten aus sechsundsechzig Ländern.
Ein solches Großprojekt ergibt schon deshalb Sinn, weil die gesamte Gruppe der Eulen mehr als zweihundertsiebzig Arten umfasst, vom winzigen Elfenkauz bis zum Riesenfischuhu. Anhand der neueren Forschungsergebnisse will Ackerman mehr über die Fähigkeiten und Leistungen der so verschiedenen Mitglieder dieser Vogelordnung vermitteln. Was sie den Lesern dazu präsentiert, ist spannend, manchmal geradezu atemberaubend.
Eulen können Töne dreidimensional orten
Eulen sind Prädatoren mit einem weiten Beutespektrum von kleinen und mittelgroßen Säugetieren über Vögel und Insekten bis hin zu Aas – selbst von gestrandeten Walen in Kalifornien. Sie sind das (meistens) nachtaktive Gegenstück zu den Taggreifvögeln und haben im Laufe ihrer Evolution durch die Verschiebung des Aktivitätsgipfels eine eigene, konkurrenzmeidende Nische geschaffen. Um sich in der Dunkelheit zu orientieren und Beute zu machen, haben sie raffinierte Anpassungen entwickelt: Superaugen, Spitzengehör und leiser Flug.
The large eyes are moved from the sides to the front for space reasons, creating a human-like face, which is unique among birds. If human eyes were in a comparable relationship to the body, they would weigh just under two kilograms. The pupil can take up almost the entire eye; the cones responsible for night vision are particularly densely packed on the retina.
The ears have large, asymmetrical openings, the dense plumage of the facial disc serves as a sound funnel, with each feather being controllable by a muscle. The sensory hairs of the fourfold enlarged cochlea are constantly being renewed. Owls can locate sounds in three dimensions. Part of the auditory nerve branches off into the visual center, creating a visual image of what is being heard. The northern great gray owl can locate mice in their burrows under a fifty centimeter thick layer of snow.
In years of famine, the larger boys eat the smaller ones
In order to be able to surprise their prey, owls have developed almost silent flight. This is possible because their dense plumage is velvety soft, and the very elastic flight feathers are comb-like on the front and frayed on the back to avoid air turbulence. Such a sound-absorbing effect will be used in bionics in the future to make aircraft and wind turbine rotor blades quieter.
Communication in the dark is best achieved acoustically. Owls call a lot and in a wide variety of tones or noises. Each individual in a population can be distinguished by their voice. The low frequency of the calls allows maximum range with minimal effort. Many species remain silent during the day and are excellently camouflaged by their spotted plumage, for example when they nestle motionless against a tree trunk whose bark they can hardly be distinguished from.
Since owls cannot digest the bones, hair, or feathers of their prey, they regurgitate ball-shaped pellets containing these remains. The analysis of found debris not only deciphers the spectrum of prey animals, but also allows statements to be made about their occurrence and frequency – especially in the case of mice and other small mammals, which are just as difficult to detect as their hunters.
When raising their young, many owls have to cope with a very fluctuating supply of food animals; think of the cycles of lemmings and other rodents. The number of eggs per clutch can vary between three and ten. In years of hunger, the larger young eat the smaller ones so that at least some of the brood can survive.
Twenty years ago, owl research meant hard, frustrating field work, and finding nests hidden in tree hollows was a game of chance. Practically nothing was known about some species. With technological advances and multidisciplinary approaches, knowledge about hidden owls has grown enormously. This is thanks to nest cameras, endoscopes, directional microphones with continuous recorders, radio telemetry with miniature transmitters, sound spectrography, neurophysiological and new molecular biological methods.
Ackerman has turned this information into a stimulating and readable book, even if she occasionally overextends her enthusiasm for night birds. It may also be tricky to translate zoological terms correctly, but a few slip-ups (claws instead of talons, American robin translated as robin instead of migratory thrush) should have been noticed by the editors. On the other hand, the extensive bibliography and the neat index are to be welcomed.
Owls see and hear what we cannot perceive, like to play, have excellent spatial memory and are intelligent in their own way. That’s why the author considers whether they have consciousness. After all, they can express both sadness and joy, and there is evidence that they dream of catching mice during REM sleep. So can we empathize with the way these birds live? Ackerman confronts us with many fascinating facts. But what it’s like to be an owl will continue to remain hidden from us.
Jennifer Ackerman: “The Wisdom of Owls.” The most mysterious bird in the world and its talents. Translated from English by Sebastian Vogel. dtv Verlag, Munich 2024. 376 pages, illustrations, hardcover, €26.
