132 Spotted Crake habitat use
©Wildfowl & Wetlands Trust
Wildfowl
(2013) 63: 115–134
and especially willow scrub, that in the
absence of management interventions will
result in the loss of the very complex system
of vegetation and shallow water that exists
today.
Home ranges
The minimum convex polygons calculated
for the radio-tagged birds in Lille Vildmose
were remarkably restricted, the core ranges
being 0.33–0.56 ha in extent. These were
substantially less than those in the studies on
the Ouse and Nene Washes (4.3–31.2 ha;
Mallord 1999) and the Insh Marshes
(1.3–5.1 ha; Mackenzie 2000), but in those
studies, the positions of radio-tagged
individuals suggested movement between a
number of discrete core areas used through
the season, implying movement between
pockets of suitable habitat which were
exploited to a greater extent than areas in-
between. The birds in Territory 1 and 2
at Lille Vildmose tended to remain in
small pockets of suitable habitat (a pool
surrounded by shallow
Typha
swamp, and a
ditch line with pools, swamp vegetation and
reedbeds, respectively) surrounded by
unsuitable habitat (drier
J. effusus
/
G. fluitans
wet grassland,
Molinia
grassland and dry
grazed grassland). The bird in Territory 2
did, however, visit Territory 1 on a number
of occasions and relocated there before the
transmitter ceased being detected. This bird
probably showed a similar movement
between blocks of suitable habitat, perhaps
as a result of the desiccation of its core
habitat occupied throughout most of June
and July (also reported by Schäffer 1999 in
his studies of radio-tagged Spotted Crake).
In contrast, the pair in Territory 3 occupied
an area of similar size over the same time
period without being seemingly constrained
by marked changes in habitat in the
surrounding area. Unfortunately, we know
nothing about how the type and extent of
habitat affects reproduction in Spotted
Crake, but the fact that all birds remained
within such a small area through a major
part of the breeding period suggests that all
three males were associated with breeding
attempts that kept them confined to these
relatively small areas of wetland within a
greater matrix of habitats.
Conclusions
Despite the radio-tracking data providing
considerable insight into the size of home
ranges used by Spotted Crake at Lille
Vildmose, there is still little concrete
information about the specific habitat
features that they select. We consider that
consistent shallow water is important,
although the depth of water and the
associated vegetation community seems of
lesser importance. There were massive
emergences of Odonata (dragonflies and
damselflies) from all such shallow water
areas, regardless of vegetation type, as
evidenced by cast exuvae in the study area
(especially those of the Four-spotted Chaser
Libellula quadrimaculata
in the early season, A.
Fox unpubl. data). It therefore seems likely
that the presence of shallow water to
support the larval stages of these and the
many other arthropod species which emerge
into the terrestrial environment for the
imago stage could potentially supply a
substantial source of food items both for
adults and growing young (Taylor & van
Perlo 1998). The most important feature to
