The Bittern Botaurus stellaris is a secretive and elusive streaky-brown heron that lives in reed-beds. It eats small fish as well as amphibians, invertebrates, small birds and mammals. The Bittern is a rare bird, with a UK population not more than about 100 birds, its numbers swollen in winter by small numbers arriving from Europe. We are fortunate to have Bitterns regularly over-wintering at Tring, particularly at Marsworth, but sometimes also at Wilstone. One or more have been present almost every winter since 1980 and for probably much longer. Some anglers brave enough to be close to the reed-beds at dawn or dusk on a cold winter’s day might have been lucky to see one, but looking for a brown streaky bird in amongst a mass of brown streaky reeds in poor light makes seeing them a bit of a challenge! If you have visited RSPB’s Minsmere reserve or one of the other breeding sites during the early breeding season, you may have heard the male Bittern’s eerie booming call – once heard, never forgotten - like a distant low fog-horn, which is used to attract mates.
The Bittern was once widespread and one was known to have bred at Wilstone in 1849, leading Walter Rothschild of Tring Park fame to wonder, in his writings, whether one would return to breed again. But it didn’t and the Bittern became extinct in Britain in the 1880s as a result of the widespread drainage of wetlands for farming and from hunting. It retuned to Norfolk to breed again in 1911 and was present at Tring during the breeding season for a few years during the late 1920s, but it didn’t breed. Since then, national numbers have gone up and down and towards the end of the 1990s it was almost extinct again.
In the early 1990’s, working through the United Nations, the international Convention on Biological Diversity was agreed, which led to Biodiversity Action Plans (known as BAPs) being drawn up in the UK, to provide national and local county strategies for the conservation of 391 different species and 45 distinct habitats, of which the Bittern and its wetland habitats were two. Since that time, the number of priority species has risen to 1,149 and a further 20 important habitats have been added.
The reed-beds of Marsworth and Wilstone are the largest in Hertfordshire, which makes them one of the most important sites for Bitterns in the region. In 2001, the Herts and Middlesex Wildlife Trust, which manages Wilstone, along with the Friends of Tring Reservoirs became part of a national initiative, led by the RSPB, to significantly increase the area of suitable reed-beds for Bitterns in an attempt to double the number of booming males. Nationally, the project has been very successful and its 2010 targets have already been achieved. Even at Marsworth in recent times, a Bittern has been heard to boom, albeit briefly, in 1999 and again in early 2008.
Using reed-bed management experience from all over Europe, work has been carried out to improve the reed-beds for the benefit of Bitterns in partnership with the reservoir’s owners, British Waterways, which has kindly funded the work. The reed-beds are regularly monitored for their quality and several years ago at Wilstone, wire fences were installed in the water to encourage the spread of the reeds out into the reservoir so that even when the water level drops, as it does every autumn, some reed will still be growing in deep water, which Bitterns prefer.
At Marsworth, where the water levels are more stable, some much more visible work was carried out during October. A ‘Truxor’ amphibious reed-cutting machine was on site for a week, cutting a number of channels and pools into the reed-beds, to increase the length of reed exposed to open water. This should encourage fish to enter the reedbed from the open water of the reservoir, providing greater access for young fish as well as increasing the accessibility to Bitterns. And in addition, removal of the cut reed and the resulting re-growth of the reeds should help to remove nutrients from the water, thus improving the water quality in the reservoir, in turn improving the habitat for both fish and Bitterns.
Further reed cutting work was carried out in late 2009 and it is hoped that funding will continue to be available for further work in future years, with the objective of attracting one booming male Bittern or better still, a breeding pair of Bitterns by 2014. What a success that would be.
I am indebted to Tim Hill of Herts and Middlesex Wildlife Trust and others for their contributions to this article. The historic Bittern records are from ‘Birds at Tring Reservoirs’ by Rob Young, Jack Fearnside and David Russell 1996.
(Last updated 05/2010)