Booming bitterns
Resonating across wetlands in spring, the evocative calls of male bitterns are a sign that the ‘ bull of the bog’ is thriving in Britain in numbers not seen, or heard, for centuries.
Back from the brink, bitterns were once faced with extinction in the UK but now appear to be thriving in our wetlands
“The thing about bitterns,” says photographer Oscar Dewhurst, “is you’re not meant to see them”. He should know, as he’s just spent months patiently trying to capture these amazing birds on camera. The second part of the species’ scientific name Botaurus stellaris means ‘starry’ and describes the speckled plumage of their back, flanks and wings, but could equally refer to their celebrity status in UK birding and conservation circles. Just as important are the streaks running from throat to undercarriage – used to best effect when one of the birds adopts its namesake ‘bitterning’ posture, with neck stretched and bill pointing skyward. As a watcher, you could blink and the bird will disappear, replaced by a clump of reed stems with googly eyes.
We love this spooky, cryptic heron. We love its striking looks and avant-garde posturing. We love its names, arguably the best dialect aliases of any British species – butter-bump, bull-of-the-bog, mire-drumble, bog-bumper – and dozens more. We love the weirdness of the male’s call, to which all of these nicknames allude – a bass ‘boop’ so low-pitched it literally bumps your guts. But it wasn’t always so.
In some communities, the sombre, disembodied boom reverberating over miles of reed and mire was once thought to foretell death. Bitterns were heavily persecuted, while the less superstitious hunted them for meat. This pressure, on top of habitat loss as wetlands were drained for agricultural purposes, drove the species into a steady national decline throughout the 18th and 19th centuries. By the 1880s, it was doomed to extinction here and – sickeningly – many of the last records were of eggs and skins taken by collectors.
Fortunately, we got a second chance. Bitterns continued to turn up in Britain as winter visitors and began breeding again in 1911. This natural recolonisation continued, aided by an increase in wetland areas following wartime flooding and changes in land use. By the 1950s, records show around 80 booming males, mostly in Norfolk and Suffolk. But the recovery was short-lived. From the late 1950s, loss of habitat again took a serious toll – in part, this was a result of deliberate agricultural drainage, but many reedbeds simply dried out and gave way to scrub in a natural process of succession.
Population boom
By 1997, there were only 11 territory-holding male bitterns in Britain. A second extinction seemed imminent. But fast-forward two decades to 2018 and at least 188 males could be heard booming in wetland landscapes anywhere from East Anglia to Somerset and from Wales to northern England. This was the 12th annual increase in as many years, and the same period has also seen
We love the weirdness of the male’s call – a bass ‘boop’ so low-pitched it literally bumps your guts.
the number of nesting attempts and the number of sites where bitterns are known to occur increase steadily.
The most spectacular population increases have been in Somerset’s Avalon Marshes. This area is now a large wetland complex of RSPB, Natural England and Somerset Wildlife Trust reserves (as well as privately owned reedbeds), where numbers of booming males increased from none in 2006 to 50 in 2018.
The species is even doing well in London, where it has wintered at the London Wetland Centre since the early 2000s, making sightings at least theoretically possible for millions of people, among them the young Oscar Dewhurst. “I saw my first bittern at RSPB Minsmere when I was 10,” he says, “but then I discovered they could be seen in London and it seemed almost too good to be true. I started visiting the London Wetland Centre at weekends and school holidays, spending hours sat in the same hide. Sometimes I’d be lucky, most times not, but I kept going back.”
Something in the water
A few years later, Oscar found himself back at Minsmere, where his success in capturing pictures has earned him the nickname ‘bittern boy’ among other photographers. It’s getting easier, not least because there are more birds. “There was a female at Minsmere in autumn 2018 that was ridiculously bold. She spent hours fishing out in the open, within 5m of the hide, seeming unfussed by people coming and going. I watched loads of people get great shots, thinking ‘hang on, I’ve spent hours and hours here, and now there’s this bird just sauntering about…’” Oscar laughs. “It’s an amazing change, really.”
So, what exactly has changed? RSPB bittern specialist Simon Wotton has been monitoring their numbers for almost 15 years and says that, in a nutshell, conservationists finally worked out what bitterns need. Reedbeds are essential, of course: the larger and wetter, the better. Moreover, within patches of reeds, bitterns are edge-lurkers, spending most of their time within 30m of open water. Recognising that habitat was key in the mid-1990s, the RSPB took a lead in managing and restoring the few sites where bitterns remained.
Heroic efforts were made to lower the levels of dried out reedbeds. This was far
from easy – bogs and heavy excavation equipment do not mix. Expensive machines were lost and at least one trapped crew member had to be winched to safety by a rescue helicopter.
Need for reed
Meanwhile, brand new wetland reserves were being created, including at Lakenheath Fen in Suffolk and Ham Wall in Somerset. Both featured extensive new reedbeds on what had been arable land and peatworkings, respectively. It can take the best part of a decade, or more, for a new reedbed to mature into prime bittern habitat, but the task doesn’t end there because, for bitterns to thrive, the reedbeds have to remain in the early, wet stage of succession. In a natural system, the disruption caused by flooding, tidal surges or even ice movement periodically scours and renews the beds and prevents them lifting and drying out as their leaf litter accumulates.
The same renewing effect is created by reed cutting. This traditional activity all but died out in many areas, due to dwindling demand for thatching materials, but has been reinstated for conservation purposes, with the material removed now more likely to be used in soil conditioning products for gardeners or as biomass fuel for power stations.
In addition to reed cover for nesting and roosting, says Simon, bitterns need access to food. They are patient fishers along the reed edge, and target mainly rudd, eels and other smallish fish, along with small mammals and aquatic invertebrates. Fish tend not to venture more than a few metres in among reed stems, so these margins are vital.
For females, access to enough food during the breeding season is critical. Males play no part in parenting, and if a female has to travel a long way to find good fishing, longer absences mean her young are at significantly greater risk of predation than if she could hunt nearby. On the flipside, she will avoid nesting too close to the fishing area. There is a fine line between convenience and conspicuousness.
Despite their increasing numbers, bitterns still aren’t easy to watch – and for birders, the challenge adds to their allure. Secretive and skulking by nature, bitterns are seldom seen flying, preferring the cover of reeds. Their legs aren’t as long as those of grey herons, and so, rather than wading, they make stately progress, stepping carefully on the loose matrix of reed stems, using their long toes to spread their
It can take the best part of a decade for a new reedbed to mature into prime bittern habitat.
weight. Flights are most easily observed in the breeding season, when females shuttle to and fro, provisioning the young (usually four to six of them) in the nest. When leaving the nest to hunt, the female goes to considerable lengths to do so as inconspicuously as possible, creeping some way through the reeds before taking flight, and landing at a similar distance on her return, to avoid giving predators a clear idea of the location of her young.
The long game
Habitat creation and restoration on the scale seen in several reserves over the last 25 years doesn’t happen quickly or cheaply. But the effort has been gratifyingly effective – species recovery has been much faster on sites that have been managed for bitterns. The work continues – currently one of the most ambitious projects is in Cambridgeshire, where another new RSPB reserve is being developed in the wake of massive sand and gravel extraction. The Ouse Fen project won’t be complete until 2030, but by then it will be the largest reedbed in Britain – a 4.6km² paradise for bitterns. We may be living with uncertainty in many ways, but for the stars of Britain’s bogs, at least, it’s boom time.