The Bittern – Botaurus stellaris – or Eurasian Bittern is a thickset heron with yellowish-brown plumage on upperparts, golden patches mottled and streaked black. It has on broad, rounded, bowed wings with reddish-orange primaries. Underparts are paler, with vertical dark streaks. Breast, belly and flanks are heavily streaked with reddish-brown. Throat is pale yellowish-brown. The head, crown and nape are black, the bill is yellowish-green. The eyes are yellow or reddish-orange and the legs and feet are greenish. Both sexes are similar.
A secretive bird, very difficult to see, as it moves silently through reeds at water's edge. They are a wetland species found in wetlands in the UK with large reedbeds. Bitterns are most visible in winter at certain RSPB reserves such as at Minsmere, Suffolk and Leighton Moss, Lancashire.

Bitterns eat fish, amphibians and insects.

The males make a remarkable far-carrying, booming call in spring, often given at dusk and dawn. Male bitterns begin to boom as early as late January to establish territories and attract mates. There is no pair-bond as such, and the male normally takes no part in nest building or raising the young.

The nest is a shallow platform of reed stems. A clutch of 5-6 olive-brown eggs are laid. Incubation starts with the first egg, lasting for 25-26 days. and hatching is stretched out over a period of several days. The young are cared for by the female. The young fledge at 50-55 days of age, and become independent soon afterwards. Females are able to breed successfully in their first year.

In the UK, widespread declines caused by drainage and particularly persecution, led to the extinction of the bittern around 1885, having already disappeared from Northern Ireland by 1840. The species returned to Norfolk in 1900, and was proved to breed in 1911. Since then the breeding population slowly built up, though never reaching Scotland or Ireland. 

Having reached a peak of about 80 booming males in the 1950s, the species started to decline again shortly after, beginning in the Norfolk Broads, and despite a slow recovery during the 1990s, reached a low point of 11 booming males in 1997. Since then, the numbers have steadily increased.

This reduction in numbers was accompanied by a contraction in the range of the species, and during the 1970s and 80s it ceased to breed in several counties. Today, only a handful of birds survive, mainly in Norfolk, Suffolk and Lancashire.

The root cause of the sustained decline was loss and impoverishment of the reed habitat. This was exacerbated by high mortality during cold winters. Traditional management of reedbeds for cut reed maintained the reedbeds in good condition for bitterns. As the need for reed declined, many reedbeds were lost as they dried out through neglect or were drained for other agricultural uses.

A new survey by the RSPB and Natural England shows Britain’s loudest bird is bouncing back, following intensive conservation efforts, which has seen its population rise over the last 15 years from 11 males in 1997 to 104 this year.