Bittern Boom! Another increase in booming male bitterns in 2018


New data released by the RSPB at the end of September revealed 188 booming male bitterns in the UK in 2018, representing another successful year for this scarce bird.

The Bittern is a shy and elusive member of the heron family that is affectionately known by a variety of nicknames, including bog-bull, bog hen, bitter bum and boom bird. Inhabiting reed bed habitat, their brown streaky plumage means they blend perfectly into the background. Its possible to walk straight past a bittern without knowing its there, and this, coupled with their shy habits, makes this a hard bird to survey. Thankfully, the male birds become rather conspicuous in spring when they make a remarkable booming call (i.e. the boom bird) that can be heard up to five kilometers away. This deep, foghorn-like call is formed when powerful muscles expel air from the oesophagus. Researchers estimate bittern numbers by counting the number of booming males within an area.

The streaky brown plumage of bitterns enables them to blend into their reedbed habitat

The population history of the bittern in the UK is somewhat of a proverbial rollercoaster. Despite being a common breeding species in the early 1800s, by the 1880s bittern numbers had dramatically crashed and the species was extinct as a breeding bird in the UK. Natural recolonisation saw their numbers increase through to the 1950s when there were roughly 80 booming males, before another decline saw just 11 booming males in 1997. Since then conservation efforts have seen numbers begin to increase again.

Efforts to increase bittern numbers involve creating bittern-friendly habitats and, in particular, bittern friendly reedbeds. Channels and small pools within reedbeds form the favoured hunting grounds for bitterns, where they walk stealthily or wait patiently for small fish and other prey. Designing reedbeds to incorporate plenty of these features ensures ample hunting grounds. Additionally, reserve waterways have been stocked with eels, a favourite food of the bittern. RSPB Old Moor is one fantastic example where reserve design has facilitated bittern nesting. Situated near Barnsley, this reserve now flourishes on an area of former wasteland that was known locally as ‘Hell’s Kitchen’ due to the regular fires that would break out there. Careful reedbed design and eel stocking means that 2-3 bittern pairs now nest at this site each year, not bad for a reserve that only opened 20 years ago.

Similar efforts across many reserves have seen bittern numbers steadily increase since the late-1990s from 11 booming males in 1997 to 166 in 2017 and then to 188 in 2018. Additionally, booming males are now being recorded at a greater number of sites than they were 20 years ago. While only a subset of sites are monitored for nesting activity, 2018 saw 79 nests where female bitterns were feeding young across 37 sites.

The increase in booming males (red) and sites with booming males (blue) since the 1990s. Data source: RSPB

The past 20 or so years can be tentatively viewed as a conservation success story for bitterns in the UK and as a fine example of what can be achieved through studying a species and implementing a habitat management program to assist in its recovery. Only the future will tell if the current increase is another temporary peak within the historical rollercoaster of the UK bittern population. But, through continued habitat management, there’s real hope that bittern numbers will continue to increase and that the boom of the bittern will once again be heard in all corners of the UK.

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