The RSPB has announced that the bittern had a record-breaking year in 2021 with 228 individual males counted, up from 209 in 2019.
The success story is due to conversation efforts that have restored and recreated the birds’ wetland habitats over the past few decades.
The Eurasian bittern is a member of the subfamily Botaurinae, part of the family Ardeidae, which also includes herons and egrets. Bitterns tend to be more secretive than other members of the family, frequenting reed beds and other marshy areas, and rarely venturing into the open.
Also known as the great bittern, it is a shy and elusive, thickset bird with pale brown plumage with dark streaks and bars, which help it blend in with the surrounding vegetation. When disturbed it will freeze in an upright position with its bill pointed upwards in an action known as bitterning. To further camouflage itself, long feathers on its throat and shoulders droop downwards over the neck to obscure the outline of its head and body.
It is known for the male’s loud booming call, which can be heard from up to 5 km away. These foghorn-like calls can reach volumes of about 100 decibels, and it has been suggested that they gave rise to the bittern’s name derived from the Latin buteo meaning hawk, and taurus meaning bull, because the call resembles the bellowing of a bull. Other colloquial names include “barrel-maker”, “bog-bull”, “bog hen”, “bog-trotter”, “bog-bumper”, “mire drumble”, “butter bump”, “bitter bum”, “bog blutter”, “bog drum”, “boom bird”, “bottle-bump”, “bull of the bog”, “bull of the mire”, “bumpy cors”, and “heather blutter”.
Before advances in science, it was not known how the bittern produced such a low-pitched, loud noise. One explanation was that it lowered its head and blew into the water as noted in The Wife of Bath, one of the best known of Geoffrey Chaucer’s Canterbury Tales; “And as a bitore bombleth in the myre, She leyde hir mouth unto the water doun:” (“And as a bittern booms in the quagmire, She laid her mouth low to the water down:”).
In 1922 in a paper entitled The Function of the Oesophagus in the Bittern’s Booming, published in The Auk, the peer-reviewed journal of the American Ornithological Society, now renamed Ornithology, James Chapin, ornithologist, and curator of the American Museum of Natural History, wrote about an American bittern the museum received, which had some unusual thickening of the skin on its neck.
After numerous experiments, which involved inflating the neck of the bittern with air using a glass tube, Chapin concluded that the bird made the sound by inflating its oesophagus, keeping it expanded with flaps near the tongue. To inflate the oesophagus, the bittern pushes its head forward, quivers its body, and opens and closes its bill making a series of grunts that sound like hiccups.
Once the oesophagus is fully inflated the bittern raises its head and exhales the air to produce between 4 and 10 deep, resonant booms, repeated at 1-2 second intervals. The sound is similar to that made when blowing over the neck of an empty bottle or jug.
Male bitterns begin booming from late January to establish territories and to attract a mate. They continue to boom throughout the summer and although it’s not clear why this is researchers from the University of Pisa found that females looking for food for their chicks foraged in areas occupied by booming males. The study was inconclusive, but one suggestion is that the males’ booms help the females find food to feed to their offspring.
The best time to hear a bittern’s boom is on a warm, still day when sounds carry further, between April and June at dawn or dusk, although they can also be heard at night or any time of the day.
Because each bittern’s boom is unique, conservationists can identify individual birds by recording the sounds and estimate the population size in a particular area.
Bitterns were once widespread in wetland environments across the UK, as were little bitterns, night herons, and purple herons. (The latter three disappeared for good in the 1600s only to return as rare visitors.)
They were popular in medieval feasts roasted and dressed or served in a game pie. At the investment of George Neville as the Archbishop of York in 1466, 204 were served as part of the celebration meal, almost as many as the population today.
In Wheate 300 Quarters; In Ale 300 Tunne; Wine 100 Tunne; Ipocrasse one Pype; oxen 104; wilde bulles 6; Muttons 1000; veales 304; porkes 304; swannes 400; geese 2000; capons 1000; Pygges 2000; Plover 400; Quayles 150 dozen; foules called Rees 200 dozen; peacocks 104; mallards and teales 4000; cranes 4000; kyddes 204; chyckyns 2000; pigeons 4000; conyes 4000; byttors 204; herenshawes 400; fessantes 200; partridges 500; woodcocks 400; curlews 100; egrittes 1000; stages, buckes, and Roes 500 and mo.; Pasties of venison colde 4000; parted dyshes of gelly 1000; playne dishes of gelly 3000; colde tartes baked 4000; colde custards baked 3000; Hot Pastries of Venison 1500; Hot custards 2000; Pykes and Breames 608; porposes and seales 12; spices, sugared Delicates and Wafers plenty.
However, by the late 19th century they became extinct as breeding birds, as a result of wetland drainage for agriculture, persecution, slow breeding, and hunting for food. They were also sought after by egg collectors and taxidermists, and it’s said that there are more stuffed bitterns in Norfolk than there are live birds.
Back from the brink
From 1911 they began to recover with numbers rising to about 80 booming males by the 1950s. But it was a precarious existence and by 1997 the population had declined to just 11, with the bittern once again on the verge of extinction in the UK.
With funding from the EU, the RSPB embarked on a project to study bitterns and make recommendations based on their findings to try and prevent their loss once more. Because bitterns are so secretive, lightweight radio transmitters were attached to bitterns at two RSPB reserves so that their movements could be tracked. The RSPB also looked at the types of habitats in which bitterns prefer to live, the food they require, as well as nesting requirements and the diet of chicks.
Between 1996 and 2000, the project restored reedbeds at 13 sites in East Anglia, raising the water levels, controlling the vegetation, and reshaping pools and ditches in the reedbeds.
From 2002 to 2006 further work was done to develop a wider network of reedbeds for breeding birds as well as wintering bitterns. Improvements were also made to encourage more fish into these areas, giving bitterns more food to eat, which improved their breeding success.
Since then, the population has steadily increased, and prospects look to be good. Having re-established themselves in the southeast, the population is beginning to spread north and into Wales. The hope is that one day they will return to Scotland and Ireland where they are currently only rare winter visitors.
The population is still at risk, particularly from climate change and rising sea levels. If salt water flows into coastal reedbeds, they will become uninhabitable for bitterns so the RSPB is creating several new reedbeds inland, including at Lakenheath Fen in Suffolk and Ouse Fen in Cambridgeshire.
This article was originally published by Birdspot.co.uk. Read the original article here..