Forest Monkeys reveal secrets

The Dutch name for Little Bittern is Woudaap, which in direct translation means Forest Monkey.  Last weeks work involved a great deal of nimble movement through reedbed ‘forests’, culminating in the Somerset Forest Monkeys revealing some of their secrets.

We started with a good deal of thrashing about in the reedbeds at Minsmere.  Thinking about climate change, the impact of too many Red Deer, and natural succession in an ageing reedbed.  How are we going to manage this site over the next 25 years?  Nothing beats getting into the habitat and experiencing it close-up to understand what needs to be done.

Then on to Snape, where new wetlands are being created.  A bit of electro-fishing to understand how the fish populations are developing, then a look at the area currently being created to add a few tweaks to the design; imagining yourself in a metre of water surrounded by reeds and thinking what features would attract a feeding Bittern or a Great White Egret.

Then down to Ham Wall, where after a summer of meticulous recording by a superb group of volunteers and local birders, we soon homed in on the Little Bittern nesting and feeding sites.  Water depths, edge profiles, reed characteristics were all recorded and some electro-fishing revealed the secrets of the Forest Monkeys favoured feeding areas.  Such details will be invaluable in creating similar habitat elsewhere.

One interesting fish caught in some numbers at Ham Wall was the Moderlieshen or Sunbleak Leucaspius delineatus, a non-native species that has a highly developed life history strategy. The majority of cyprinid fish species take 2-4 years to become sexually mature and spawn just once a year. The females scatter many thousands of eggs over aquatic macrophytes or gravel,and these are then left unguarded and vulnerable to predation.  Unusually for cyprinids, the Moderlieshen become sexually mature at one year old and are batch spawners, with females laying several batches of eggs, between April and July, which are guarded by the males until they hatch. They were first recorded in the Somerset Levels around 1990, their origin unknown but likely to have arrived via some fish stocking by anglers.

Photos above - Moderlieshen, Little Bittern nest.

Island Mere in ruddy health

Rudd (top), Roach and the new Island Mere hide.  Note head shape and mouth structure of the fish.

Electro-fishing the Island Mere at Minsmere usually has to be a quick affair so as not to upset too many visitors. However, this week it was more leisurely as it is closed to visitors while a new island mere hide rises from the marsh. The hide traditionally provides excellent views of Bitterns on the edge of the mere and it was along these margins and in the adjacent ditches that we concentrated the fishing effort. The results were spectacular – an estimated fish biomass of 74 kg/ha - one of the best recorded at Minsmere. Roach formed the bulk of the biomass, but with significant increases in Rudd and Perch. Tench, 3-spined and 9-spined Sticklebacks made up the remainder of the catch.

Research has shown that Rudd are a major food source for breeding Bitterns whilst Roach are less important. Why should this be for two apparently similar fish? The answer probably has to do with differences in their behaviour. During the daylight hours of the summer months, Rudd tend to hide amongst the reedy marginal vegetation, thus making themselves easier to catch by Bitterns. By contrast, Roach spend more time out in the open water amongst weeds and away from the margins. However, in the winter months, both species move into deeper, more sheltered ditches and Roach are likely to be more available to feeding Bitterns. Given good water levels in the spring, the signs are good for breeding Bitterns next year.

Earlier in the week, on another site, I looked at the nesting site of a pair of Cranes. They can be remarkably secretive in the breeding season and tend to choose a secluded nest site surrounded by shallow water. The nest often looks out over a small clearing in the wetland where they can see the approach of predators. This particular nest clearing is growing over fast and work will be required this winter to open it up a little. However, whilst the young chicks will feed around the nest, it is the quality of the wider foraging area that will determine the likelihood and speed of the chicks fledging. Invertebrate-rich, tall vegetation, preferably in wet (squidgy) conditions is a key requirement.

Ouse Fen comes of age (what a tinca!)

Ouse Fen from the air and at boat level; a stunning Tinca (Tench) and a not-so-stunning stickleback

Amongst the headline figure of 104 booming Bitterns in the UK this year was the smaller milestone of the first successful nesting of Bitterns at Ouse Fen (Needingworth Quarry) in Cambridgeshire. The partnership project between Hanson and the RSPB will eventually become Englands largest reedbed as the habitat is created following gravel extraction.  A day spent reviewing progress was very instructive. The aquatic habitat in the developing reedbed compartments looked superb, with abundant aquatic weeds including the scarce Fan-leaved Water-crowfoot and Hairlike Pondweed.

A search for the now redundant Bittern nest was easy enough, thanks to excellent triangulation by the guys recording the birds activities during the long watches required to prove breeding. The typical small woven platform of reeds was constructed in what would have been about 60-70 cm of water at the time. All the feeding flights were from the nest location across to ‘Phase 1’, the oldest reed compartment. A further couple of hours of electro-fishing provided the reason for this. The relatively young area of habitat around the nest has few fish as yet, just a few sticklebacks, but the more mature compartment supports a respectable fish biomass of around 21kg/hectare, mainly Perch and Roach. This is above the 10kg/ha considered to be the threshold for successful Bittern breeding. So why did she not nest where the fish were? The simple answer is that the dry spring had reduced water levels in the reeds in ‘Phase 1’, thus reducing the security of any nest. However, the story is even more complicated. There were no booming males heard at Ouse Fen yet there was a nest. At nearby Fen Drayton, there were 2 boomers yet no nest. It is likely that the dry spring also affected the reedbeds at Fen Drayton and as a result the female moved across to the wetter Ouse Fen to find a secure nest location. Thus she found a mate, a nesting site and a food source in three different locations.

The electro-fishing also produced a few Tench; surely one of the most stunning of our freshwater fish with those golden scales. Less visually attractive, although interesting in a rather gruesome way, was the high parasite load of the Nine-spined Sticklebacks. The photo above shows one poor specimen with a bulging abdomen containing a Schistocephalus tapeworm (S. pungittii is the usual species in this stickleback). If that wasn’t enough it also has myxosporidium cysts (a protozoan parasite) to contend with.

Family parties of Bearded Tits (one of three) and Marsh Harriers were additional evidence that this new site is coming of age. A single Garganey, a few Little Egrets and several Hobby all helped round off a pleasant day in a boat.

Non-stop fishing (a two Ruff(e) trip).

Put together a nice reedy edge and a good population of Rudd to get a booming Bittern. Bittern photo by Andy Thompson.

Bitterns basically have simple requirements; tall, wet vegetation full of food. In the UK, this means reedbeds and fish. As the reedbed tour continues, this week we looked at fish populations and started at Titchwell. The reserve had one ‘boomer’ and one successful Bittern nest this year. Electro-fishing produced fair amounts of Rudd and Eels, both key prey for Bitterns, and the reedbed restoration some 5 years back has produced a good reed edge.

The freshmarsh at Titchwell is currently undergoing a make-over. Reed around the margins has been blitzed and islands have been re-profiled and re-levelled. Expect good birds over the coming years! Today the nearly dry marsh had plenty of waders around the diggers, but thankfully nothing rare: 200+ Dunlin, 100+ Golden Plover, plenty of Ruff, 10+ Whimbrel and a Garganey.

Strumpshaw Fen was the second stop of the tour. Despite the dry spring, Strumpshaw has surpassed itself this year with up to 4 boomers and 3 nests (usually only 1-2 boomers, with no nesting). The electro-fishing provided the answer: 2 years after a major saline inundation and fish kill, the fish population has rocketed. We caught 6 species at a biomass of 20+kg/ha of fish less than 300g (twice the estimated threshold for Bittern breeding). Personally, I was pleased with a fish ‘tick’ – Ruffe. We flushed a Bittern from the ditch with the highest fish density, Water Rails squealed, and the young Bearded Tits and Marsh Harriers everywhere pointed to a good breeding season. An Otter performing in front of the hide (a regular event this year) underlined the resurgence in fish populations.

And finally, a look around the reedbed at Otmoor. The catch here was mainly Pike and Perch, indicating an early stage in the development of the fish community. It will be a year or two yet before Bitterns boom here.  Two Little Stints, a Ruff, Hobby and 14+ Red Kites in the general area added to the interest.

Below: the freshmarsh at Titchwell takes shape.