Great bittern booming accompanied by amphibians | głos Bąka

The Eurasian bittern or great bittern (Botaurus stellaris | Bąk in Polish) is a wading bird in the bittern subfamily (Botaurinae) of the heron family Ardeidae. 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.

The nest is usually built among reeds at the edge of bodies of water. The female incubates the clutch of eggs and feeds the young chicks, which leave the nest when about two weeks old. She continues to care for them until they are fully fledged some six weeks later.

With its specific habitat requirements and the general reduction in wetlands across its range, the population is thought to be in decline globally. However the decline is slow, and the International Union for Conservation of Nature has assessed its overall conservation status as being of "least concern".

Usually solitary, the Eurasian bittern forages in reed beds, walking stealthily or remaining still above a body of water where prey may occur. It is a shy bird, and if disturbed, often points its bill directly upwards and freezes in that position, causing its cryptic plumage to blend into the surrounding reeds, an action known as bitterning. While in this position, the shield of elongated feathers on throat and breast droop downwards and hide the neck, so that the outline of the head and body is obscured. Sometimes it resorts to applying powder down produced by patches of specialist down feathers at the side of its breast. This white dusty material seems to help it to rid its head and neck of slime after feeding on eels. It then removes the excess powder by scratching vigorously before applying preen oil from the gland at the base of its tail.

The bird has a secretive nature, keeping largely hidden in the reeds and coarse vegetation. Occasionally, especially in hard winter weather, it stands in the open beside the water's edge, although usually close to cover to facilitate a hasty retreat. In flight, its wings can be seen to be broad and rounded, and its legs trail behind it in typical heron fashion. Its neck is extended when it takes off, but is retracted when it has picked up speed. It seldom flies however, except when feeding young, preferring to move through the vegetation stealthily on foot. Its gait is slow and deliberate and it can clamber over reeds by gripping several at a time with its toes. It is most active at dawn and dusk, but also sometimes forages by day.

The mating call or contact call of the male is a deep, sighing fog-horn or bull-like boom with a quick rise and an only slightly longer fall, easily audible from a distance of five kilometres on a calm night. The call is mainly given between January and April during the mating season. Surveys of Eurasian bitterns are carried out by noting the number of distinct male booms in a given area. Prior to modern science, it was unknown how such a small bird produced a call so low-pitched: common explanations included that the bird made its call into a straw or that it blew directly into the water. It is now known that the sound is produced by expelling air from the oesophagus with the aid of powerful muscles surrounding it.

Recording took place during moon eclipse in the vicinity of Milicz Ponds in Barycz Valley (Stawy Milickie / Sarni Rów / Dolina Baryczy)

Amphibians heard on the recording:
European fire-bellied toad (Bombina bombina | Kumak Nizinny)
Edible frog (Pelophylax kl. esculentus | Żaba wodna)
Marsh frog (Pelophylax ridibundus | Żaba Śmieszka)
European tree frog (Hyla arborea | Rzekotka Drzewna)

Field recording gear:
Audio Technica AT4022 pair in SASS array
Sound Devices Mixpre-3 II

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