Restoration of reedbeds for bitterns at Minsmere RSPB Nature ReserveFrom estimates of 12 to 14 calling male bitterns at Minsmere between 1971 and 1973, numbers declined to just one calling male, with no evidence of breeding, in 1991. This mirrored a similar national decline with numbers falling from 70 to 80 calling males in the 1950s to a low of just 11 calling males in 1997. Although work had been carried out over the years at Minsmere to maintain open water in pools and ditches, the underlying problem of a gradual drying out of the reedbed had not been addressed. Therefore between 1994/5 and 1999/2000, 48.75 ha of mature reedbed were lowered using machinery to halt succession and re-establish wet reedbed. At the same time, ditches and pools within the reedbed were reprofiled to be more “˜bittern-friendly’ and overall hydrological control of the reedbed was improved. As a result the number of calling male bitterns on the reserve increased to 7 in 2000 – a trend that is continuing with 10 in 2007. Populations of other important reedbed species were either maintained or increased by this work.
Minsmere RSPB Nature Reserve , 52.2473731, 1.619388699999945
Country or Territory:
Freshwater Ponds & Lakes
Area being restored:
Royal Society for the Protection of Birds (RSPB)
NGO / Nonprofit Organization
Primary Causes of DegradationOther
The reedbeds at Minsmere formed during the Second World War when parts of the coastal grazing marshes were deliberately flooded as an anti-invasion measure. Subsequently natural succession resulted in the gradual drying out of much of the area. Although management was carried out to remove invading scrub and to maintain pools and ditches, the underlying issue of accumulating leaf litter was not tackled. As a result, large parts of the reedbed became dry and unsuitable for breeding and feeding bitterns. The number of calling males fell to just one in 1991 and there was no proof of breeding.
Reference Ecosystem Description
At the start of the restoration project, the reedbeds at Minsmere covered 157 ha and were approximately 50 years old. Towards the western end of the reedbed there is a broad fringe of mature alder carr. The reedbed consisted of two hydrological units, separated from each other by a bank running approximately diagonally from south-west to north-east. Apart from the Island Mere (7 ha) there was comparatively little open water within the reedbed apart from ditches. Encroaching scrub was limited as the result of removal works in the 1980s and early 1990s. A small scale 7 year rotational cutting programme, approximately 3 ha per year, was initiated in 1991/2. Much of the reedbed was dry with large amounts of accumulated leaf litter. In addition to bittern, the reedbed supported the following nationally important species (5 year mean figures) marsh harrier Circus aeruginosus (8 nesting females), bearded tit Panurus biarmicus (16 pairs), gadwall Anas strepera (14 pairs), pochard Aythya ferina (5 pairs), otter Lutra lutra (1 pair) and water vole Arvicola terrestris (unknown but considered to be low and declining based on casual observations).
The objective of the project was to maintain the internationally important suite of reed-dominated communities to increase breeding bittern numbers to 10 calling males (c25-30% of UK population) and 12+ nesting females; increase bearded tit numbers to 50+ pairs (c12% of UK population) and marsh harriers at 8 to 10 nesting females; and to benefit wintering wildfowl, otter, water vole and specialist reedbed Lepidoptera and fen/carr Diptera.Reedbed is a priority habitat for conservation in the UK and there is a national target to create an additional 1,200 ha by 2010. Additionally, there is a national Species Action Plan (SAP) for bittern with 4 key objectives (at the time of the start of the work at Minsmere these were): initially, to maintain a population of at least 20 calling males; increase the population to 50 calling males by 2010; achieve a population of not fewer than 100 calling males by 2020; and increase the number of sites supporting calling males to 22 by 2010. In the light of the success in increasing bittern numbers and distribution, these figures were revised in 2007 to: 110 calling males at 44 sites by 2020 and 190 calling males at 64 sites by 2030. Species and Habitat Action Plans in the UK are developed jointly by the statutory conservation agencies, conservation NGOs and private landowners, as appropriate. For both reedbeds and bitterns, the RSPB is the lead organisation. Therefore this project had the potential to make a significant contribution to achieving the short and medium term objectives of the bittern SAP (and those of other key reedbed species).
The project does not have a monitoring plan.
The whole area is owned by the Royal Society for the Protection of Birds (RSPB). The Minsmere reedbeds are the third largest in England. The overall planning of the work formed part of the revision of the reserve’s management plan and part of a national emergency recovery programme for bitterns funded by the European Union’s LIFE-Nature programme. Given the site’s status as a Site of Special Scientific Interest (SSSI), Special Protection Area (SPA), Special Area of Conservation (SAC) and Ramsar site, all of the planning was carried out in conjunction with the government’s statutory conservation body, English Nature (now Natural England), the Environment Agency and Local Council.
Description of Project Activities:
Over the winters of 1994/1995 to 1999/2000, 48.75 ha of dry reedbed were lowered using excavators to remove up to 30 cm of leaf litter and topsoil to create early successional wet reedbed. The excavated material was used to create low banks within the reedbed to form 8 hydrologically-separate units. During the excavation process, all old ditches and pools were re-instated and reprofiled to be more bittern-friendly, having gently sloping sides extending up to 4 m from the centre of the ditch. This profile allows the development of very wet ditch and pool margins which are used by fish such as rudd Scardinius erythrophthalmus, eels Anguilla anguilla and nine-spined sticklebacks Pungitius pungitius which earlier research had shown to be important prey for bitterns. In total 8.1 ha of new open water was created and 10.78 km of ditch reinstated or excavated. Again based on earlier detailed research by the RSPB into the habitat requirements of bitterns, the shape of pools and ditches was such that they provided the maximum amount of reedbed/open water edge. Prior to the excavation of each area, the area was drained and burnt to remove tall standing reed to reduce the amount of material needing to be removed and to make machinery access and working conditions easier.
Ecological Outcomes Achieved
Eliminate existing threats to the ecosystem:
Reed re-establishment has been good in all of the excavated areas and bitterns, on average, began feeding in the excavated areas within 6 months and nesting within 2 to 4 years. The bittern breeding population at Minsmere increased to 6, possibly 7, calling males and 9 nesting females in 1999. Radio-telemetry studies of Minsmere bitterns proved that young birds reared on the reserve were colonising other reedbeds in eastern England and playing a key role in the national recovery of the species. Continuing research and population modelling have shown that distance from the core Suffolk coast population of breeding bitterns, particularly Minsmere, is a key factor in determining whether a restored or new reedbed is likely to be colonised by breeding bitterns.Of the other key species, marsh harrier, bearded tit and pochard numbers remained stable, gadwall numbers doubled, otter numbers remained stable, water voles increased markedly (with the reserve becoming one of the top 14 sites for the species in England) and all of the important reedbed Lepidoptera continued to be recorded on a regular basis. The water vole increase is partly thought to be the result of the provision of additional breeding habitat provided by the new low banks within the reedbed. There is a clear link between the reedbed lowering work and the increase in bittern numbers and the technique has now become standard practice for reedbed restoration throughout the UK.
Factors limiting recovery of the ecosystem:
In terms of reedbed recovery after excavation, the main factors that can influence the rate of recovery are: too much physical damage to the reed rhizomes by heavy machinery; frost damage to the rhizomes if they are exposed to very cold weather during the excavation process; and grazing of young reed by coots Fulica atra and geese, especially greylag geese Anser anser. Luckily during the work at Minsmere none of these was a serious problem, though one area did suffer some "˜knock back' by frost and grazing. Wildfowl grazing can be discouraged by keeping the excavated areas damp but not flooded until the young reed is reasonably well grown - the absence of surface water both deters wildfowl from using the area and also makes eating the reed shoots harder.In terms of recovery of bittern numbers, this is reliant on there being either a "˜resident' population that is maintained or the site being within colonisation distance of an occupied site. Encouragingly, radio-telemetry has shown that bitterns disperse over quite large distances. Also, it is important that there is a good supply of fish for bitterns.
Socio-Economic & Community Outcomes Achieved
Economic vitality and local livelihoods:
The increase in bittern numbers at Minsmere has meant that the chances of visitors to the reserve actually seeing a bittern has increased dramatically and it is very clear from comments received that visitors feel a great deal of excitement and satisfaction at seeing a bittern.
Key Lessons Learned
The project has been an outstanding success and bittern numbers have continued to rise at Minsmere, with 10 calling males in 2007. As mentioned earlier, it has been demonstrated that young bitterns reared at Minsmere are a prime source of birds colonising other reedbeds in eastern England. The reedbed lowering technique developed on the reserve has become standard practice for reedbed restoration in the UK and, as long as care is taken with respect to mechanical damage to rhizomes and controlling grazing of young reed by wildfowl, the technique should be applicable for the majority of sites.Longer term, it will be necessary to create new reedbed further inland as all of the existing freshwater habitats on the reserve are susceptible to saline incursion as the result of climate change-induced flooding. Given the evidence that the Suffolk coast bittern population is the key “˜driver’ to the successful recovery of the species nationally, the significance of this risk is highlighted by the fact that in 2007, 9 of the 27 known nests of bittern in the UK (33%) were at Minsmere. Therefore any loss in reedbed or breeding females on the reserve in the short to medium term is likely to have a significant impact.
Long term management of the reedbed is a combination of rotational cutting, improved hydrological control and, ultimately, re-excavation of parts of the reedbed. Whilst bitterns were the prime target species for this project, as explained the site is being managed for the full suite of important reedbed species and therefore it is important that the full range of successional stages is maintained. Fortunately, the Minsmere reedbed is of sufficient size that this is possible.
Sources and Amounts of Funding
RSPBEU LIFE-Nature fund – project “˜Urgent conservation action for the Bittern in the United Kingdom’Amarada Hess