Fen Management Handbook - Scottish Natural Heritage

Islands above winter water levels within the wider, deep channels of a duck marsh can be allowed to
vegetate for use by breeding wildfowl. Where breeding wildfowl are specifically being encouraged,
relatively constant water levels during the breeding season are required. This prevents flooding
of nests, loss of feeding areas whilst also ensuring the growth of aquatic plants that maintains
invertebrates and fish populations for duck species. Preferably wetland habitat being managed
for breeding duck should be at least 5 ha in extent, offering well vegetated and sheltered, nest and
feeding sites. The structural complexity of a waterbody is important for some breeding wildfowl, with
complex shorelines of a long length in relation to the area of water supporting the largest densities of
ducks and coot (Fuller 1982). Favoured as suitable nesting sites are well vegetated islands greater
than 100 m2 surrounded by deeper water. Extensive areas of sheltered shallow water (up to 0.3 m
deep for dabbling duck and 1.0 m for diving duck) close to suitable nesting areas provide the areas
necessary for adults and young broods to forage. Merritt (1994) provides further guidance on the
design and management of habitat suitable for breeding wildfowl, including the control of the island
vegetation. Species such as coot and moorhen will breed in small pools surrounded by emergent
vegetation where nest platforms are constructed.
Monitoring and maintenance of good water quality is critical as aquatic vegetation, invertebrate
and fish are very susceptible to water pollution e.g. contamination by agricultural run-off. Such a
deleterious impact upon these food resources profoundly affects the suitability of waterbodies to
waterbirds.
Sensitive periods
Species breed within this habitat largely from March to August, so disturbance should be minimised
within this period which includes avoidance of damaging mechanical operations. Disturbance
should also be minimised during prolonged periods of cold winter weather when waterbirds
energy expenditure increase at a time frozen waters reduces the availability of, and access to, food
resources.
Reedbed specialists and birds of mixed fen swamp
Habitat features
The features included here are those areas of tall monocotyledon plants including common reed,
sedges, reedmace and rushes that grow as both emergent plants and on waterlogged ground
within a fen. If these plants are growing as a margin to open water then their management has been
addressed as a separate habitat.
Recommended management
The management of reedbeds for birds, other wildlife and as a crop is detailed in Hawke and José
(1996). For the flagship reedbed specialist, the bittern, many breeding sites have been identified as
containing over 20 ha of wet reedbed with ditch and pool systems that give access to fish. Such
large reedbeds are also used by bearded tit, reed and Savi’s warbler but many of the warblers
associated with such features in fens can occur in much smaller areas, less than 1 ha if suitable
habitat is present. A prerequisite for Cetti’s warbler occupying reed beds is adjacent areas of carr
or retention of scattered bushes within the swamp, this is also beneficial as foraging areas to reed
warbler. Encroachment of scrub must however be controlled to allow no more than 10% of the
swamp to develop into woody vegetation (Merritt 1994).
The ability to control water levels in swamp is critical to maintaining conditions optimal to ensure
the growth of aquatic water plants, including reed, and to maintain good invertebrates and fish
populations. The latter (preferably of rudd, eels and sticklebacks) are important food resources
in reed-beds for bittern. During the breeding season constant water levels are also important to
prevent flooding of nests and loss of feeding areas. In wet reed, summer water levels should be
maintained so as not to vary beyond 0.1m and 0.25m in depth (Merritt 1994). Bitterns amongst
other waterbirds prefer wet reed with open water, Merritt (1994) suggesting open water ponds of
a 0.25-1 m depth covering a maximum of about 10% of the surface area. The margins of ditches
supplying water into the reed-bed should slope gradually (1 in 10) providing foraging areas for
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