Eurasian Bittern (Botaurus stellaris)
Bitterns are thickset herons with bright, pale, buffy-brown plumage covered with dark streaks and bars, similar in appearance to the American bittern, Botaurus lentiginosa. As its alternate name suggests, this species is the largest of the bitterns.
Distribution and habitat
Distribution in Europe as a whole is estimated at 20-44,000 males. It usually inhabits Phragmites reed beds. The population is declining in much of its temperate European and Asian range. It is resident in the milder west and south, but migrates south from areas where the water freezes in winter. In the UK, the main areas have been Lancashire and East Anglia with an estimated 44 breeding pairs. However, the Lancashire population at Leighton Moss has declined in recent decades, while bitterns have been attracted to new reed beds in the West Country. In Ireland, it died out as a breeding species in the mid-19th century, but in 2011 a single bird was spotted in County Wexford and there have been a number of subsequent sightings.
Usually solitary, the Eurasian bittern forages in reed beds, walking stealthily or remaining still above a body of water where prey may occur. If it senses that it has been seen, it points its bill directly upwards and becomes motionless so that its cryptic plumage causes it to blend into the surrounding reeds: an action known as bitterning. It is most active at dawn and dusk.
Males are polygamous with each mating with up to five females. The nest is built in the previous year’s standing reeds and consists of a platform some 30 cm (12 in) across. Four or five eggs are laid in late March and April and incubated by the female. After hatching, the chicks spend about two weeks in the nest and then disperse amongst the reeds.
Bitterns feed on fish, eels, amphibians and invertebrates, hunting along the reed margins in shallow water.
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 3 mi (4.8 km) on a calm night. “Butter bump” and “bitter bum” were onomatopoeic colloquial names for the bird in some localities. Others, each unique to a particular part of Great Britain, include “bog blutter”, “bog-bull”, “bog bumper”, “bog drum”, “boom bird”, “bottle-bump”, “bull of the bog”, “bull of the mire”, “bumpy cors”, “butter bump” and “heather blutter”. The number of names is one indication of how widespread they used to be. 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.
The 18th-century Scottish poet James Thomson refers to the bittern’s “boom” in his poem “Spring” (written 1728), published as part of his The Seasons (published 1735): “The Bittern knows the time, with bill ingulpht / To shake the sounding marsh …”
And the loud Bittern from the bull-rush home
Gave from the Salt-ditch side the bellowing boom:
Thomas MacDonagh, the Irish poet executed for his part in the Easter Rising, translated a famous Gaelic poem by Cathal Buí Mac Giolla Ghunna “The Yellow Bittern” (“An Bonnán Buí” in the Irish). His friend and fellow poet Francis Ledwidge wrote a celebrated “Lament for Thomas MacDonagh” with the opening line “He shall not hear the bittern cry”.
In the Sherlock Holmes novel The Hound of the Baskervilles by Sir Arthur Conan Doyle, the villain Stapleton proposes the boom of a bittern as an explanation for the howl attributed to the mystical hound.
Because of its secretive and skulking nature, it was then unclear exactly how the bittern produced its distinctive booming call. One early theory held that the bittern thrust its beak into the boggy ground of the marsh in which it lived, making its vocalization which was amplified and deepened as it reverberated through the water. A reference to this theory appears in Chaucer‘s The Wife of Bath’s Tale, lines 972-73: “And, as a bitore bombleth in the myre, She leyde hir mouth un-to the water doun …” 
However, the English physician Sir Thomas Browne disputed this claim, stating in his Pseudodoxia Epidemica, Book III, Ch.27: “That a Bittor maketh that mugient noise, or as we term it Bumping, by putting its bill into a reed as most believe, or as Bellonius and Aldrovandus conceive, by putting the same in water or mud, and after a while retaining the air by suddenly excluding it again, is not so easily made out. For my own part, though after diligent enquiry, I could never behold them in this motion …” Browne even kept a captive bittern, in order to discover how exactly its “boom” was produced.