Guest blog by Mark Solomons, Minsmere resident and volunteer

The boom train has arrived on time again this year - no, not another political euphemism but a Minsmere event that just three decades ago would have seemed unimaginable.

Bitterns. The iconic, noisy, reclusive reedbed residents that are rightly considered to be one of this reserve's signature species.

They are booming, both literally and metaphorically. Having lived in Minsmere for more than 18 months their echoing call has become part of the soundtrack to my lockdown life.

I've been fortunate to see a few in flight but it was only last weekend that I got my first ever sighting of one on the ground from, appropriately, Bittern Hide. It poked its head up above the reedbeds for a split second and I thought that was it but then it carefully crept closer and closer until it was obligingly near enough to take pictures.

Bittern by Mark Solomons

It ducked and dived among the green shoots of new reeds, head held low as it surveyed the water then up again as it checked to see who was watching (four of us, socially distanced, in the hide and a hobby perching on the dead tree a few yards away.)

What a treat. I actually felt my heartbeat racing afterwards. It felt special seeing what I'd been listening to for so long. I got back and decided to read up about them.

Apparently, and I guess many of you already know this, but the number of booms in a row is called a boom train and can range from one or two in succession during the early months of the year right up to six or seven in a row during the height of the summer. Even before the booming starts there is a warming up ritual called grunting - basically a clearing of the throat and strengthening of the throat muscles which allow it bellow later on.

It is the males who boom and each one makes its own noise, creating an audible fingerprint. This makes it easier to monitor numbers. In the 1990s those numbers fell to just 11 males across the whole of the UK putting it on the brink of UK extinction and not for the first time. For 100 years earlier it had practically died out as a result of hunting, slow breeding and, predictably even then, the loss of the reedbeds on which it relies.

Before then the species had been fairly common across the country earning several regional nicknames such as bog blutter, buttle, miredrum and bumbagus and, according to Chaucer, 'a bombleth in the myre'. Although solitary, they occasionally group together to form a sedge, pretence or a siege of bitterns. The animal world has always given wordsmiths free range when it comes to collective nouns.

Over the 20th century numbers crept up gradually but it was always a precarious existence and many parts of their traditional breeding grounds disappeared as reedbeds were badly managed or neglected. By the 1990s it was decided something had to be done if we were to keep these birds in Britain at all and, helped by a grant from the EU, the RSPB pioneered a project to restore bittern habitats across 13 suitable sites.

This involved not just growing reeds but maintaining water levels within them, reshaping pools and ditches and controlling the growth of other vegetation in the area that could affect reedbed survival. Some of this is quite complicated hydro-engineering with networks of pipes and sluices linking dozens of pools and water channels so that when water levels drop in one it can be raised with water taken from another.

The project worked. There are now almost 200 male bitterns across the country leading it to be named the RSPB's 'Bird of the Decade' last year. As someone who lives and works near an area of Suffolk within earshot of a reedbed habitat, the boom of bitterns was the soundtrack to my lockdown summer last year. It's as good as any Spotify playlist to be tapping at a keyboard to suddenly hear that unique noise joining the other, more familiar birdsong of the seasons.

As for the sound itself, boom suggests a cannon firing and though it has been recorded at 100 decibels in volume, it is not an ear shattering sound. It is far more musical than that. Less Brian Blessed shouting, more The Righteous Brothers during the first few bars of You've Lost That Loving Feeling.

Others have described it as similar to the sound made by blowing the top of a milk bottle or those jugs in bluegrass music from America's deep South. For me, it's not so much a 'boom' as an 'oom' - try going 'boom' from the back of your throat but without moving your lips.

The reason, timing and consistency of the booming was looked at by researchers from the University of Pisa at the beginning of the century in a paper for the Italian Journal of Zoology. It was inconclusive to say the least as the booming from one set of bitterns did not appear to match the patterns from a colony in a different area.

The first booms are clearly designed to attract a mate but the males continue to boom after chicks are born and the Italian team believe this may be a way of protecting a feeding territory and letting the mothers know where they can come to grab a fish or amphibian that they can give to their offspring. It appears to be the only paternal duty the fathers bother with.

Seeing them is harder and may become harder still without the protection of their environments which will constantly remain under threat whether it is from creeping urbanisation to specific projects such as the building of Sizewell's new nuclear facility bordering the reedbeds of the, currently thriving, bittern population at RSPB Minsmere on the Suffolk coast.