Botaurus stellaris
Bulky, golden-brown heron with thick neck and short legs. Largely unmistakable but skulky behaviour makes it difficult to observe, as it generally forages hidden in reed-beds. Plumage mottled above, with coarse stripes below. Primaries and most secondaries with dark barring, in contrast to paler coverts. May recall Eagle Owl in flight with broad, rounded wings and retracted neck, but wings are bowed and legs trail behind tail. Crown and moustache stripe black in adult and brown in immature birds. Betrays its presence by it's far reaching song.
Flight call a deep croaking "graat". 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).
Wikipedia: map (se also Xeno-canto below)
Birdlife ecology