Essex Biodiversity Project
Identification - The Bittern is a large mid brown bird slightly smaller than a grey heron but more compact and stocky. (Mullarney et al 2001) It is a very shy bird, rarely seen but the males can be heard with their distinctive booming. It flies infrequently. It will adopt the 'bitterning posture' when alarmed - hiding in reed beds with the bill pointing straight up.
General ecology - the main habitat bitterns are found in are dense reed beds where they feed on fish and amphibians. It is a rare and declining bird and has been recorded in Essex in the winter at Abberton Reservoir, Old Hall Marshes and Lee Valley. Britain is an important wintering site for bitterns, often from Northern Europe. If bitterns stay for any length of time at a site this indicates a good feeding site.
Current threats are loss of habitat such as reed beds, habitat degradation food availability and small population size.
Surveying tips - the best way to survey bitterns in Essex is to look at wintering sites. Both male and females of all ages winter in the UK and it can be difficult to sex or age them in the field. Despite this it is still important to count them. The best way to count bitterns is to watch them flying to their roost at sunset - One visit in the middle of each month between September and April with several surveyors. The best time to watch is during the two hours before darkness. You can find this out by looking up the official sunset time (often in newspapers) and start watching half an hour before that. Estimate the numbers flying to the roost.
SAFETY - anyone going out near a wet reed bed habitat should ensure they know the area and are able to walk safely out after dark. Do not go into the reed beds!
As the bittern population increases, the chances of us getting a breeding bird in our area increases. It is important for the RSPB and Natural England monitoring team to know about all the booming birds, so if any of you hear booming coming from a reed bed next spring please let us know.