Spotted Crake habitat use 131
©Wildfowl & Wetlands Trust
Wildfowl
(2013) 63: 115–134
dominated large areas of the management
unit used by birds in Territories 1 and 2, but
which were never occupied by crakes during
radio-tracking. Birds did however use a
broad spectrum of vegetation types, ranging
from areas of open water with submerged
macrophytes, through
Typha
and
Phragmites
swamp, to the inundated
Alopecurus/Glyceria
wet grassland south of Hegnsvej. North of
Hegnsvej, the crakes again used very
different habitat, mostly
Phragmites
swamp
with encroaching willow scrub, with an
extensive understorey of
E. angustifolium,
C. demissa and J. articulatus
not present
elsewhere. This area was very gently shelving
and retained shallow water throughout the
entire study period, but the vegetation here
was generally much higher and thicker than
in the management units elsewhere that held
crakes.
The few similar studies of radio-tagged
Spotted Crake in the past have given a
similar picture. Mallord (1999) found
that his birds at the Ouse and Nene
Washes, England used Common Spike-rush
Eleocharis palustris
swamp, dense sedge
Carex
beds, Amphibious Bistort
Polygonum
amphibium
stands as well as Reed-grass
Glyceria maxima
marsh with stands of
Bulrush
Scirpus lacustris.
Mackenzie (2000)
showed that birds in the Insh Marshes,
Scotland used Water Horsetail
Equisetum
fluviatile
and Bladder Sedge
Carex vesicaria
swamps, but rather avoided Bottle Sedge
Carex rostrata
and
Carex rostrata/
Marsh
Cinquefoil
Potentilla palustris
tall herb fen,
whilst showing strongest avoidance of
Molinia/
Tormentil
Potentilla erecta
mire and
drier Sheep’s Fescue
Fesuca ovina/
Common
Bent
Agrostis capillaris
grasslands. Likewise,
the structure of the habitats in which their
Spotted Crakes were active varied, with
vegetation height varying substantially with
vegetation type and season.
It does therefore seem that shallow water
is the defining feature of Spotted Crake
habitat (after Mallord 1999; Schäffer 1999;
Gilbert
et al.
2002) and that birds generally
will avoid deepest water (here considered to
be > 40 cm throughout the summer) and
those areas that become totally dry during
their residence (as suggested by Cramp &
Simmons 1980 for the breeding areas and by
Taylor 1987 for wintering sites in Zambia).
Vegetation characteristics (
i.e
. the structure,
the species present and, to some extent, the
trophic status of the ground water) seem to
be of less importance. This may explain the
comparative rarity of the species however,
since shallow water systems tend to be
seasonally ephemeral and to dry out in
the course of the spring and summer,
whereas constant shallow water seems to
characterise sites used by Spotted Crakes as
breeding habitat, from arrival in April until
the end of the breeding season in August/
September. These types of habitats tend to
be associated with spring-fed mires, valley
mires, gently shelving lake shores with
abundant but disturbed vegetation and
wet seasonally inundated grasslands. The
habitats exploited by the species at Lille
Vildmose in this study, are by contrast,
artificial and likely to disappear in the longer
term due to vegetation succession. All the
sites presently occupied by the species are
characterised by vegetation that represent
the early stages of colonisation of bare wet
peat substrates and all are being invaded by
more aggressive species, such as
Phragmites
