The natural sound that blends sorrow and hope

From deep within the swathe of reedbeds at RSPB Titchwell Marsh I can hear the low, mellow tones of an alto clarinet. There is no melody or intonation, just a single note which hints of sadness, as if the musician is lost in his own melancholy. The sound echoes across the wetlands a second time. Now more forceful, richer, suggesting purpose and expectation. It's a strange fusion of sorrow and hope and I feel impelled to find the source.

Reedbeds develop where the water table is above ground level for most of the year. These areas are often peppered with ditches and pools, adding structural diversity. Deep water pockets are excellent for fish communities seeking refuge from predators in the shallow margins. Gentle bank gradients provide easy access to seasonally dry areas where amphibians and reptiles sunbathe on hot summer days. Although reedbeds may not seem ideal for mammals, abundant supplies of fish and small amphibians attract fresh water otters, whilst secluded, well-vegetated banks are perfect hideaways for shy, reclusive water voles. In summer, tall, golden stems of the common reed produce spikelets with tufts of silky purple hair. They sway in unison; feathery fronds all facing in the same direction as they lean away from the wind. At first frost the delicate leaves break away from their sheaths falling into the water, layering the bottom with reed litter. Here aquatic invertebrates pupate and thrive. Reedbeds are indeed dynamic eco-systems which support a treasure trove of wildlife, including one very intriguing species - as I am about to discover.

Sitting low in the reeds almost invisible amongst the tall grass, a small member of the heron family stalks the water's edge with intent. His striped under belly and plumage blend in perfectly with varied hues of brown vegetation and it takes me a while to spot this iconic wetland bird. He stealthily guides his thickset body through the muddy water then stops and with exact precision drives a long beak into the reeds to retrieve a small fish. Dinner for one.

As if he senses someone watching, the bittern stops frozen - neck outstretched and bill pointed upwards. Motionless, apart from his long neck which sways in time with the reeds around him, the point of his bill perfectly emulating reed tips. He remains stationary for some time then confident that he is not in danger from predators continues his quest for food. Comically lifting each leg in turn, carefully placing outstretched toes in the muddy substrate. Then unexpectedly, he dips his head, puffs out his chest and belches.

I'm surprised to realise that the resonating 'whoom' I heard before was not made by a woodwind instrument but originated from the gullet of this small wader. Bitterns can expand the muscles around their oesophagus and create an internal echo chamber; as they breathe out they emit a low-pitched sound known as a 'boom'.

Ironically, both the alto clarinet and the bittern have hovered on the edge of extinction. Once common across Britain's marshes, the bittern declined during the 1800s as watery homelands were drained for farming. Now, thanks to an intensive species recovery project, bittern numbers are on the increase but we still need to be vigilant about their future.

Bitterns feed mainly on small fish such as rudd or stickleback which inhabit reedbed margins. However, they choose to nest in the wettest part of the reedbed where the density of vegetation will deter most mammalian predators. Thoughtful structure in reedbed wetlands has been a crucial element to managing bittern recovery, but these habitats are transitional by nature. In time they will become wet woodlands so require long-term planned water management.

As spring arrives the males emit their characteristic mournful boom to attract a mate. If romance is on the cards, females may answer with a restrained version of the call. Unlike some other species, courtship is a private moment but may end with both partners performing an aerial display. Except for these brief encounters during breeding season bitterns reject the company of their own kind preferring instead, a solitary life. The best place to see one of these elusive loners is in a wetland area rich in high grasses. Their obsession with privacy means they have a number of tricks to stay hidden but at this time of year, you are likely to hear their trademark call as it carries across the reedbeds.

On a still, clear day in spring the air at RSPB Titchwell Marsh fills with a chorus of song from sedge warblers, reed bunting and Cetti's warblers. But my all-time favourite has to be the soulful and evocative sound of a lone bittern calling for his love.

You can hear their characteristic booming call at RSPB Titchwell Marsh from March onwards. For more information go to www.rspb.org.uk/titchwellmarsh