As we enter the new breeding season, Simon Wooton reflects on the results from a record year in 2023.
The story of the Bittern continues to be one of UK conservation success, with 2023 continuing the trend of a steadily increasing population. The annual survey is delivered by a dedicated team of volunteers and conservation site staff, with the kind permission of landowners, and relies on the distinctive ‘booming’ call of the males to indicate the presence and location of this elusive reedbed specialist.
In 2023, at least 234 booming males were recorded, up from 233 in 2022 and 229 in 2021, 116 of which were recorded on RSPB nature reserves, down from 119 on RSPB sites in 2022. Booming was also reported from 11 new sites in 2023, all in England.
The minimum number of booming male Bitterns (in red) in the UK and the number of occupied sites (in blue) between 1990 and 2023.
A brief history
Bitterns are dependent on reedbed habitats as they move through them at the water's edge, seeking out fish, insects, and amphibians to eat. They are the loudest bird in the UK - the males make a remarkable far-carrying booming sound in spring which can be heard three miles away and is used to establish territories and attract female mates through the season. Bitterns are well-camouflaged so the most reliable way to count them in the breeding season is to listen for this song.
From historical sources, it is clear that Bitterns once bred across the UK, giving rise to such colourful local names as bog blutter, buttle, bumbagus, myre-dromble, miredrum, bog-bluiter and butterbump. By the 1880s, however, Bitterns were considered extinct as a breeding species in the UK. Following recolonisation early in the 20th Century, initially in the Norfolk Broads, numbers increased to a peak of about 80 booming males in the 1950s, with most in the Broads. There then followed a steady decline, leading to a programme of monitoring and research to determine accurately the number of individuals at the few sites that still retained Bitterns in the 1980s and to help diagnose the causes of decline and to identify a means of halting and then reversing it.
The species returned to Norfolk in 1900 but dropped again to just 11 booming males by 1997, leaving them on the edge of a second national extinction. A research programme by the RSPB, investigated the needs of the birds. A key part of bringing Bittern numbers back up was recreating, managing and protecting their wetland habitats.
Major wetland habitat management, habitat restoration and creation are ongoing for this species and annual population monitoring is the main yardstick with which we can measure its success. Some of the best places to see and hear bitterns now are wetlands that were created, from the mid-1990s, for Bitterns and other wetland wildlife. Habitat management, restoration and creation has taken place at more than 80 reedbeds throughout the UK since the mid-1990s, and many of these sites are away from the traditional core East Anglia breeding areas, to encourage Bitterns to reoccupy their former range and give the species a sustainable long-term future in the UK.
The second Bittern EU Life project, from 2002 to 2006, was the first and largest project of its kind in the UK aimed at safeguarding a species’ habitat in the face of imminent threats due to climate change, as most of the UK’s breeding Bitterns in the 1990s were along the East Anglian coastline, where many sites are highly vulnerable to sea water inundation during storms. Climate-change models predict this will increase in severity and frequency as our climate changes and sea levels rise, meaning this continues to be a threat to conservation measures along our coastline
Surveying booming Bitterns
Annual surveys were established in 1990, using a new method that combined techniques of mapping the territories of booming males using triangulation and the individual identification of these males by the characteristics of their booming songs.
The distinctive booms of territorial males can be heard from as early as January at some sites, most typically following mild and wet winters, and can still be heard into June and rarely July. The best time to listen out for booming males is from the middle of March to the middle of May. A booming Bittern is very distinctive, but at a distance can be mistaken for a mooing cow or even a foghorn!
Often male Bitterns give a grunting call before their booming is fully developed, this grunting can be hard to hear unless you are close to the bird and it can sound very unlike full booms. Although Bitterns do boom at any time of the day, the best times to hear them are in the two hours around dawn and dusk. The time you are most likely to hear booming is about half an hour before sunrise. There is likely to be much less background (particularly traffic) noise before dawn than at dusk.
Distribution and abundance of booming Bitterns in 1997 (11 boomers at 7 sites), 2011 (104 boomers at 51 sites) and 2023 (234 boomers at 108 sites). The scaled circles range show 1-2; 3-5; 6-9; 10-13; 14+ booming males per site.
1997 2011
2023
Although just one more booming male was counted than last year, the population is booming. Over half of the UK’s Bittern population can be found on RSPB nature reserves, with several managed predominantly for their reedbeds to attract rare wetland birds such as Bittern, Crane and Great White Egret. Although most of the records are in England, with a few in Wales, Bittern were once found breeding in Scotland and Northern Ireland, and there is hope that they will once again find themselves there.
Although Bitterns are still a rare bird in the UK, there are some great places to hear and see them, e.g.:
The RSPB helps to coordinate Bittern monitoring across the country each year and collates breeding season records, through the Bittern Monitoring Programme, an Action for Birds in England (AfBiE) project.
Thank you to our Bittern survey volunteers
A large number of volunteers now help to monitor Bitterns at many nature reserves across the country, including coordinated booming surveys involving a number of surveyors to ensure that the whole site is covered from several different listening points at the same time. It is now only possible to achieve comprehensive coverage each year with help from volunteers, landowners and conservation site staff. Given increasing numbers across the country and a mild and wet 2023/24 winter, this year could see more new and formerly-occupied sites being occupied by booming Bitterns.
Natural England and the other partner organisations have played an important part in the Bittern success story of recent decades. Natural England has done lots of work on their National Nature Reserves supported management, and also with restoration/creation work on sites managed by other organisations through the Species Recovery Programme. Natural England has also co-funded the monitoring/research work with RSPB through AfBiE.