The song of the bittern is an amazing sound - a deep cow-like moo-ing noise. If you didn't know that it was a heron hiding out in the reeds you might be quite worried by the noise.
But the increase in bittern numbers is also quite amazing - have a look at the graph. The red lines show how many singing (booming) males have been recorded over the years and the blue lines show the number of sites. Both measures are important because we don't want all our bittern eggs in a few site baskets. Since 1997 bittern numbers have increased almost 7-fold - I wish my few stocks and shares had done as well!
The males are surveyed by listening for their booms - and each male has a reliably different boom so we can actually tell how long the males live and whether they have moved around or not within or between sites.
Actually, as with most species, we'd be much more interested in knowing the number of nesting females than singing males (because they aren't necessarily the same) but the loud males are far far easier to survey.
Bitterns went extinct in the UK in around 1885 and then naturally recolonised in 1900 building up to c80 pairs in the 1950s and then declining through the 60s, 70s, 80s until the RSPB pulled its finger out in the 1990s.
After some research which told us that bitterns find much of their prey in shallow water at the reed edge we started creating more reed edge and wetter reedbeds at our existing reedbed sites with bitterns (particularly Minsmere and Leighton Moss). But we also embarked on some much more ambitious projects - creating new wet reedbeds from arable fields that had been growing carrots (Lakenheath) or exhausted peat workings (Ham Wall). And with funding from the EU LIFE fund we worked with other reedbed owners and managers to create even more suitable bittern habitat.
And the graph shows that it has worked! Minsmere has been the powerhouse for this national recovery - producing lots and lots of young bitterns to go off and colonise other sites. And Ham Wall and Lakenheath are now doing their bit and adding to the numbers of fledged bitterns. This year looks like it will at least match 2008 and so the progress continues.
Bitterns have worried us a few times though - their steep population decline looked like it might really end up with 0 bitterns in the 1990s, then we started habitat restoration work and numbers started to increase so we were getting quite optimistic (or were we cocky?) after 1996 and the bitterns (aided by a cold winter) taught us a lesson by nosediving in numbers again. Then we were lulled again by years of increases up until 2005 and 2006 when numbers dropped again. If you care, and we do, you worry when the populations go down - there have been millions of pounds invested in bitterns and we don't want the value of our investment to go down the drain!
The future now looks fairly bright for bitterns - there are more sites that they could recolonise over the next few years. This means I am now breathing easier as several traditional bittern sites, including Minsmere, are threatened by sea level rise, and it's just as well that the newly-created inland sites are kicking in. In fact, the bittern story illustrates the type of conservation action that is needed anyway (more rich habitat is always a good idea) but will be even more essential as climate change becomes more and more of a factor influencing where species can exist.
Habitat creation will have to form a part of our plans to help many species adapt to climate change. Our experience with bitterns (provided the graph doesn't have too many dips over in the next few years) stands as an example of how we need ambitious habitat creation programmes in order to do the best for nature.
And that is another point - our work on reedbeds was largely driven by thoughts of bitterns but a very wide range of species have benefitted (we knew they would). Creating large areas of habitat takes time but nature reacts quickly to take advantage. Although the bitterns kept us waiting, the bearded tits, dragonflies, water voles, otters and reed warblers moved in far quicker. If you create the habitat that's good enough for a top predator like the bittern to move in then it's likely that the fish, insects, plants, mammals, amphibians and a whole range of other birds are there already!
To read more about our work on bitterns see the current issue of British Wildlife magazine written by experts from the RSPB and Natural England.