Great bittern / Rohrdommel (Botaurus stellaris)

Rohrdommel - ausgestopft - von Silberweide Naturzentrum. 2021-10-30 13.24.28 Um Naturzentrum Silberweide am Greifensee
Classification: Genus Brown bitterns (Botaurus); Family Herons (Ardeidae)
General: The Eurasian bittern or great bittern (Botaurus stellaris) is a wading bird in the bittern subfamily (Botaurinae) of the heron family Ardeidae. There are two subspecies, the northern race (B. s. stellaris) breeding in parts of Europe and across the Palearctic, as well as on the northern coast of Africa, while the southern race (B. s. capensis) is endemic to parts of southern Africa. It is a secretive bird, seldom seen in the open as it prefers to skulk in reed beds and thick vegetation near water bodies. Its presence is apparent in the spring, when the booming call of the male during the breeding season can be heard. It feeds on fish, small mammals, fledgling birds, amphibians, crustaceans and insects. [more]
Song: Song unmistakable and far reaching (up to 5 km). Pitch very deep, with timbre similar to blowing on a big empty bottle. At close range an "inbreath" is also audible (1-3 dampened, higher pitched introductory notes). [Link]
Calls: Flight call a deep croaking "graat". [Link]
Physical details: length=70-80 cm, wingspan=125-135 cm, weight=867-1940 g
Habitats: Wetland

Call: A little buzz/beep that sounds more like an appliance or app.
Call attributes: Call melody: non-musical, slow, Frequency: low (1-3 KHz),
First documented observation : 2021-10-30 in Um Naturzentrum Silberweide am Greifensee.