In considering the fauna, peatlands are
best divided into two groups, namely, the
strongly oligotrophic peat mosses (mainly raised and blanket mires) with abundant
Sphagnum and dwarf shrubs, and the mesotrophic to eutrophic rich-fens (mainly
open water transition and flood-plain mires) typically with a tall-herb sward grading
from swamp to damp meadow. In this context, valley and basin mires are best
referred to one of these two broad peatland classes according to their predominant
vegetation. The fauna of soligenous mires is considered in Chapter 9, pp. 3O1ff.
MAMMALS, REPTILES AND AMPHIBIANS
Ombrogenous mire species
The upland blanket mires form an important
part of the habitat of many vertebrates
considered under uplands in general. In Scotland, red deer range and feed widely
over blanket mires, avoiding only the very wettest ground where, like sheep, they
may become bogged-down and perish. Their treading and grazing helps to dry the
ground and promote increased tussock formation in plants such as cotton grass
and deer sedge, but also tends to suppress dwarf shrubs. Where they occur, feral
goats Capra hircus frequent these peatlands, and many mountain hares Lepus
timidus appear to live entirely in such habitats, making their forms in drier patches
or on hummocks. Foxes range over the upland mires but usually breed and lie up in
drier places. Of the smaller mammals, the short-tailed field vole is widespread and
may be abundant, at least periodically, on drier ground where vascular plants give a
dense cover. The common frog sometimes breeds in the bigger mire pools but
appears to prefer those with richer waters. The palmate newt is known to be
abundant in some acid peat pools. The adder is locally plentiful on blanket mires up
to 500 m, and the common lizard is generally distributed and common.
Some of these creatures are also found
on the lowland, acidic raised, valley and
basin mires. This is particularly so for the adder which usually resorts to damp
habitats during the summer and for the grass snake, a more southern species with
similar habits. In central Wales, the polecat (now found mainly in this part of Britain)
frequents and perhaps breeds on the lowland raised mires such as Cors Fochno
(Borth Bog) and Cors Goch glan Teifi, and was formerly found in these habitats on
the plains of the Solway. Roe deer range over and feed on the drier parts of these
lowland mires but avoid the wettest ground.
Topogenous fen species
While small mammals occur at times on
the acidic mires, these habitats are less
consistently productive for vertebrates than lowland fens. The Norfolk Broads and
their associated fens are perhaps the richest examples of this kind of peatland for
vertebrates in general. Here, the species which has the greatest impact on its
habitat is the introduced coypu, which not only lives and breeds in the reeds and
sedge-swamps and river banks, but also has a considerable effect on the
vegetation. Ellis (1965) has described the effects of coypu in the Broads, including
the cutting back of large areas of reed, sedge and reed-mace, the great depletion
of sensitive species such as Cicuta virosa and Rumex hydro-lapathum, and the
spread of others such as the resistant Lythrum salicaria. In many places, hydroseral
succession has been interrupted, modified or reversed, and even developing willow
carr may be destroyed. Sometimes, fen has been converted to black mud and
shallow water, and some 'coypu-lows' have proved attractive to duck and waders in
autumn and winter and nesting black-headed gulls and common terns in summer.
The coypus breed on platforms in swamp or in tunnels in the banks of dykes and
rivers, and sometimes make raids on farmland crops from their fen sanctuaries.
Coypu flourish in the Broads, except during unusually cold winters, when their
numbers are greatly reduced, and it is conceivable that a winter of exceptional
severity could exterminate the species in Britain.
The water vole is a widespread species
in fens but is associated more with the
open water and banks of ditches, dykes and rivers, where it burrows and breeds in
tunnels. The common, pygmy and water shrews are widespread in fen systems,
though the last is associated more particularly with wet conditions. The short-tailed
vole occurs abundantly in a wide range of fen vegetation, including the drier reed
swamps, and flourishes in the generally dense vegeta-tional cover. The bank vole
and wood mouse are found on the drier edges of fens, embankments, hedgerows,
and the latter also occurs in alder-willow carrs. In the south of England, the harvest
mouse finds a natural habitat in beds of Phragmites, Phalaris and Carex, and
makes its nest from the leaves of these plants.
These small mammals, but especially the
short-tailed field vole, are important as
prey for various predators, including short-eared owl, marsh and Montagu's harrier,
heron, bittern, weasel and stoat. The last two species also take birds, and their
eggs and young, and both of them often breed in fens in situations clear of flood
level, such as banks, holes in trees and even tall-sedge tussocks. The otter is
associated with the open water of lakes and rivers, but also frequents the
swamplands and sometimes breeds in dense sedge-beds or under fallen trees in
carr. Both fox and badger locally include these habitats among their hunting
grounds, though they usually have their dens on drier ground.
The brown hare sometimes frequents fen,
but is more at home in marshy
grasslands and meadows, and though the roe deer may feed in fen vegetation, it
too has a preference for the drier ground. Within their range, sika deer will also
frequent fen at times.
The abundance of insects over lowland
fens is an attraction to bats, and various
species feed over such ground, though they need hollow trees, buildings or caves
for roosting and breeding. The species seen over swampy ground include the
noctule, serotine, Daubenton's bat, Natterer's bat and barbastelle, pipistrelle and
whiskered.
Of the reptiles both the adder and grass
snake resort to fens in summer but in the
autumn return to drier places above water level to hibernate during the winter. The
adder is now less commonly found in fen than in peat mosses, but was once
numerous in parts of the Norfolk Broads. Both the common lizard and slow-worm
may be found at times in fen, but are much more characteristic of drier ground.
The amphibians have obvious associations
with wetlands, and both frog and
common toad are often abundant in fens, where they breed in the open water,
though the toad tends to make for drier ground after spawning. Both species are
taken as prey by birds such as the heron and bittern, and have recently declined
considerably in many areas, especially in the southern half of England. There is little
information about the ecological distribution of newts, but the smooth newt widely
inhabits many open waters which pass into fen, and the palmate and great crested
newts evidently occur in fen locally.
BIRDS
Birds of peatlands are best considered
in conjunction with those of open waters, for
some species belong to both habitats at once, e.g. many ducks, which feed on the
open water of lakes and nest in the surrounding marsh. This account is, however,
limited to species which breed within the range of vegetation already considered in
this Chapter. The grebes, which all build floating nests in very open emergent
aquatic vegetation, have been mentioned in Chapter 7. Reference should also be
made to that Chapter and to Chapter 6 for information on the populations of birds,
both wintering species and passage migrants, which frequent all kinds of wetlands,
permanent and temporary, during that part of the year outside the breeding season.
Ombrogenous mire birds
Lowland raised mires have a rather limited
breeding avifauna, consisting of sparse
populations of red grouse, meadow pipit, skylark, cuckoo, reed bunting, and curlew,
with the occasional addition of merlin, linnet, twite, snipe, teal, mallard and
shelduck. A few raised mires had colonies of black-headed, lesser black-backed
and even great black-backed gulls, but these seem mostly to have disappeared in
recent years. Still farther back, some of the ; northern England examples were
nesting places of the hen : harrier, and in Scotland raised mires may have been re-
colonised during the general recent spread of this species. Golden plover appear
no longer to nest on these mires, despite the suitability of the terrain and dunlin
seem to ! have gone also, despite their fidelity to certain coastal salt marshes
adjoining some sites. Raised mires are locally, and I at times, the winter feeding
place of some species of grey geese which appear to have a fondness for the stem
bases of Rhynchospora alba.
The birds of blanket mire are dealt with
also in Chapter 9. There is a characteristic
group of moorland species which I nests and feeds just as typically on the wet
peatland as on the dry dwarf-shrub heath or grassland. Of these, the golden plover
is the blanket mire bird par excellence, and is usually accompanied by dunlin (in
smaller numbers, mostly), red grouse, curlew, meadow pipit and skylark. Dunlin and
teal ; are especially associated with pool systems on blanket mires, : and black-
headed gull colonies, ranging from a few to 2000 pairs, breed on some blanket
mires, especially where there are swampy pools or tarns. There are a few lesser
black-backed gull colonies, and occasional pairs of great black-backed, on large
level expanses of blanket mire (flow) in some moorland areas.
Ornithologically, the most productive
blanket mires in species diversity are the
great flows of Sutherland and Caithness. Here, where there are often extensive
pool systems and peaty lochans of varying size, the usual species nest rather
sparsely, but there are also greenshank, red-throated divers, greylag geese,
wigeon, common scoters, : Arctic skuas and common gulls, widely but thinly
distributed. All these except the skua are associated with open water on the moors.
The greenshank feeds beside pools, lochs and rivers but nests on a mire hummock
or dry, stony moraine, sometimes far distant. Red-throated diver, greylag, wigeon
and scoter spend much time on the open water of moorland : tarns and nest by
preference on islands, but where there are ; no islands they breed on the
surrounding flow. Common gulls prefer tarns with islands or swampy edges for
nesting. he Arctic skua parasitises this species and the black-headed gull, and its
distribution is limited by that of its victims; the nesting site is usually a hummock or
dry place n the flow. The colonies are small compared with those in Orkney and
Shetland. In the Highlands, the boreal wood ! sandpiper has appeared in recent
years as a nesting bird in several widely separated localities, favouring swamp-
edged lochs for feeding and the surrounding blanket mire for its esting place.
A few other species nest sporadically
on blanket mire. There are a few snipe but
this species favours richer marshes and wet grassland. The merlin, hen harrier,
short-eared owl, lapwing and redshank, all nest at times in this habitat, but are
typically on drier or more productive moorland. The scaup which occasionally
breeds in northern Scotland may also favour the peaty moorland lochs and
surrounds. Although the peregrine has long been known to nest widely on ummocks
in the great peat mires of Finland, it is not known to do so in Britain, where it would
be too vulnerable to foxes and humans. Blanket mires are among the least
productive of all British habitats in terms of bird population density, but they support
a wide spectrum of species, and are interesting as the nearest equivalent to the
tundra of the Arctic.
Topogenous mire (fen) birds
The dense beds of reed Phragmites communis
so extensive in many rich fens are
one of the most important habitats for birds, and form the chief nesting place of the
marsh harrier, bittern, bearded tit and reed warbler. The first three species need
reed beds and are rarities confined to places where these occur, in inland fens and
brackish marshes, mainly in East Anglia, though the marsh harrier formerly bred
regularly in Dorset and a few other scattered places in England and the bittern
nests in Anglesey and at Silverdale in north Lancashire. The reed warbler also
nests in reed fringes along riversides, and occurs widely through England, reaching
almost to Scotland. Montagu's harrier also sometimes nests in large reed-beds and
is partly a fen and brackish marsh species, breeding in a few scattered English
localities; it is a species which has decreased again after a recovery during the
1940s
Other types of dense herbaceous fen vegetation,
with sedges, tall grasses, Iris,
Sparganium, Typha, Epilobium and Filipendula, sometimes tangled with willows or
brambles, provide the cover required for nesting by sedge warbler, reed bunting,
water rail, spotted crake, marsh warbler and Savi's warbler. The first two species
are widespread and numerous, but the water rail is more thinly scattered, and the
others are extreme rarities. The spotted crake evidently breeds sporadically and
unpredictably in swamps widely scattered over the whole country; there are
probably only a few pairs in any one year and the nest is very seldom found. The
marsh warbler is a diminishing southern England species especially associated
with managed osier beds, and is best known in the Severn Vale. Savi's warbler has
been found breeding in Kent since about 1960 and may be on the point of
colonising eastern England.
The wetter kind of mixed swamp, with standing
water usually visible, is the nesting
place of the pochard and coot, and some of these places, especially those least
accessible to humans and foxes, have large breeding colonies of black-headed
gulls. Duck such as the mallard, teal, wigeon, shoveler, tufted duck, gadwall, pintail
and garganey usually nest in rather drier kinds of fen vegetation, and some of them
breed far from the open water, on rough uncultivated ground or even moorland. The
last three species are all rare as breeders in Britain, the wigeon is mainly northern
and only the mallard is common and present in almost all parts of the country.
The moorhen nests widely in a variety
of fen vegetation from wet to dry and is
perhaps the most widespread of all wetland nesting birds in Britain. The
grasshopper warbler nests in the drier types of dense fen, widely but rather
sparingly. Other species breeding widely in drier fen, but ost characteristic of
habitats other than wetland include whitethroat, wren and pheasant Phasianus
colchicus. Drier sedge fen, grazed short by cattle or mown, and grading into
seasonally wet meadow grassland, is a favourite nesting place of snipe and
redshank. This transitional range of vegetation from real fen to the damper type of
permanent grassland is exemplified by the Ouse Washes, Cambridgeshire, which
have recently regained as nesters three marshland species long lost to the
Fenlands, the black-tailed godwit, ruff and black tern.
INSECTS
The Lepidoptera and Odonata of peatlands
are fairly well known, but information
about other insect groups is too erratic to justify presentation here.
Lepidoptera
Two butterflies occur in each broad class
of mire, the large heath and silver-
studded blue being found on peat mosses and the swallowtail and large copper on
rich-fens. The number of fen moths, however, exceeds that of peat moss species.
Only a few species are found in both classes of mire. A few, such as the rosy marsh
moth evidently belong to intermediate types of mire, e.g. poor-fen. The peat moss
species include all seven dwarf-shrub feeders and the fen species show a general
preference for Gramineae. A large group of moths is associated with Phragmites
communis and other fenland grasses, and many, e.g. the wainscots Archa-nara
spp. and Photedes spp., have stem-boring larvae.
The rich-fen Lepidoptera are predominantly
species of southern Britain, and
especially East Anglia - a pattern which reflects the distribution of their habitat.
These species have lost most ground during recent times, for their habitat has been
more extensively destroyed by drainage operations than the peat mosses. The
extinction of the British race of the large copper Lycaena dispar dispar by the
draining of the Fenlands is the best known of these impacts. The reintroduced
Dutch race L. d. batavus is maintained at Woodwalton Fen by rather artificial
methods of management, and it is apparent that there are no longer areas of
suitable habitat large enough to support a viable wild population of this species in
Britain. Other extinctions in the Fenlands include the reed tussock Laelia coenosa,
many-lined moth Costaconvexa polygrammata, orache Trachea atriplicis, and rosy
marsh moth, but the last species has been discovered at Cors Fochno,
Cardiganshire. The swallowtail is now restricted to the Norfolk Broads but formerly
had a wider distribution in the southern half of England, and some moths such as
the concolorous and Fenn's wainscot are now extremely rare and local.
Some of the peat moss moth species are
fairly widespread, e.g. the marsh oblique
barred and silver hook but even within this group many species are far less
widespread than their vegetational habitat, and are evidently limited by other
factors. The silver-studded blue butterfly is a southern species, which formerly
occurred as a distinctive separate race in its northernmost stations on the
Morecambe Bay peat mosses, where it became extinct apparently in the1920s The
large heath is a widespread northern peat moss butterfly showing a latitudinal cline
of variation in which three geographical races are distinguished; subspecies
philoxenus in Shropshire and Cheshire, tullia in northern England and southern
Scotland, and scotica in the Highlands. There is some overlap, with two subspecies
occurring in certain districts.
Odonata
In their larval stage dragonflies are
essentially creatures of open water, and so the
group as a whole is considered in detail in Chapter 7. Adult dragonflies are found in
nearly all types of habitat but since open water is usually surrounded by mire
vegetation, adult dragonflies are a moie important component of mires than of other
terrestrial habitats. The widespread Aeshnajuncea and the rare and local A.
caerulea frequently lay their eggs in Sphagnum peat pools where no surface water
is visible. A number of other species breed in waters which appear to be mires
rather than ponds, although close inspection always reveals at least small areas of
surface water.
SPIDERS
The spiders of peatlands are most easily
described under two main headings,
namely acidic or oligotrophic mires (bogs) and mesotrophic or eutrophic mires
(fens). Of the 76 species listed here which are confined to or most abundant in
peatlands, 31 are typical of mesotrophic or eutrophic conditions, 21 are typical of
oligotrophic mires, and the remaining 24 species may be found in either group. The
spiders thus tend not to be so rigidly confined to a particular type of mire as are the
Lepidoptera, probably because they are not restricted by specific food-plants.
Many of the fen species are largely confined
to East Anglia, the most notable
rarities in this category being Dolomedes plantarius, known only from Redgrave
Fen, Glyphesis servulus, recorded only from Wicken Fen and Chippenham Fen,
Clubiona rosserae, from Chippenham and Tuddenham Fens only, and
Centromerus incultus, once known from Wicken Fen and recently discovered at
Wood-bastwick marshes. Slightly less rare species which occur mainly in East
Anglia are Neon valentulus, recorded from Wicken, Chippenham and Redgrave
Fens, Foulden Common and Box Hill; Zora armillata, known from Wicken and
Woodwalton Fens, and from Morden Bog; Entelecara omissa, recorded from a
number of East Anglian fens, Ham Fen and Stodmarsh in Kent, and Askham Bog;
Hypomma fulvum, recorded from Wicken Fen, various localities in eastern Norfolk
and Suffolk and from Romney Marsh; Hygrolycosa rubrofasciata, widespread in the
Fens and with a few scattered records elsewhere, including one from Matley Bog in
the New Forest; Masogallica (records include Wicken and Chippenham Fens,
Foulden Common and Castor Hanglands); and Marpissa pomatia, which is
widespread in the Fens and Broads and known elsewhere from Shapwick Heath
and a few other scattered old records.
Other noteworthy rare fen species are
Maro sublestus, recorded only from Wicken
and Woodwalton Fens and ubh Lochan (Stirling); Lycosa paludicola, which has
been recorded from six widely scattered localities including Woodwalton Fen and
Shapwick Heath; and Donacochara speciosa, the few scattered localities for which
include Horsey Mere.
Among the commonest and most characteristic
fen species are Clubiona
stagnatilis, C. phragmitis, Gnathonarium denta-tum, Hypomma bituberculatum,
Lophomma punctatum, Porrhomma pygmaeum, Kaestneria pullata and
Bathyphantes approximatus. Some other species are about equally abundant in
fens and in oligotrophic mires, e.g. Pirata piraticus, P. hygrophilus, Antistea
elegans, Diplocephalus permixtus and Centromerus expertus.
Among the species characteristic of oligotrophic
mires, there is a group of eight
which are mainly northern or submontane in distribution and are described in
Chapter 9. These are Walckenaera clavicornis, Erigone capra, Eboria caliginosa,
Hilaira excisa, H. nubigena, H. pervicax, Maro lepidus and Clubiona norvegica. The
last named is also one of a small group of rarities which appear to be centred on
the north Midlands. Abbots Moss is the only known site in Britain for both Sitticus
floricola and Centromerus laevitarsis, although S. floricola also occurs in a few sites
in western Ireland. Carorita limnaea, a recently discovered British spider, is known
only from Sphagnum in Wybunbury Moss.
An interesting southern species is Glyphesis
cottonae which is common in
Sphagnum in valley mires at Thursley, the New Forest and in Dorset, but has not
been found anywhere else in Britain, and thus has perhaps the most clearly defined
habitat of any peatland species.
Apart from those already mentioned as
being abundant in fens as well as
oligotrophic mires, some of the most characteristic species of lowland oligotrophic
mires, although not restricted to them, are Arctosa leopardus, Dolomedes fimbri-
atus, Theonoe minutissima, Walckenaera nodosa, Hypselistes jacksoni,
Trichopterna thorelli and Aphileta misera. Species most abundant in northern
oligotrophic mires but also occurring in the south are Silometopus elegans,
Notioscopus sarcinatus and Drepanotylus uncatus.
Two species whose habitat perhaps comes
nearer to open water than to mires are
Argyroneta aquatica and Tetragnatha striata. A. aquatica, the water spider, is
widespread in Britain but local, and occurs in a wide range of habitats, including
valley mires, well-vegetated ponds and ditches, and even brackish water on
Romney Marsh. T. striata is unusual in that it lives mainly among Phragmites
standing in open water, well away from the shore of lakes. Its apparent rarity may
be linked to its inaccessible habitat; it has been recorded from a number of widely
scattered localities, including Horsey Mere.
A number of characteristic peatland species
also occur in coastal habitats,
especially salt marshes and sand dunes, widespread examples being Clubiona
phragmitis, Arctosa leopardus, Pirata piraticus, Gnathonarium dentatum and
Hypomma bituberculatum.
