Spotted Crake habitat use 121
©Wildfowl & Wetlands Trust
Wildfowl
(2013) 63: 115–134
measurements taken within each quadrat,
otherwise these values were set to zero.
Surface water area, area of mud and area of
dead vegetation was also recorded by
estimating the percentage of these features
present within each 1 m × 1 m quadrat.
Quadrats were defined as those with crakes
present or crakes absent, depending upon
whether they fell within the minimum
convex polygon areas calculated for each of
the radio-tagged birds in each of the three
management units (see below for details; in
the case of Territory 3, the area of the
female was taken because this encompassed
most of that of the male). In the case of one
bird in Territory 2 (Fig. 1) that moved from
its core area of use (a ditch line) into
Territory 1, we restricted the minimum
convex polygon to just the core area, so as
not to include vegetation in areas likely only
traversed by this individual.
Vegetation analysis
Detrended correspondence analysis (DCA;
Hill & Gauch 1980) was used to classify the
community composition of vegetation
within the quadrats on the basis of the
combined percentage cover of all species
present, using the PAST freeware software
(Hammer
et al
. 2001). We used DCA because
such cover data do not conform to
assumptions of linearity required for other
ordination techniques, but the method is
highly effective in reducing the complex
relative abundance scores of species into a
series of sample scores that can be depicted
on axes. In this case, for simplicity, we
restricted our presentation to scores of
quadrats and species on the first two sample
scores or vegetation axes. Since plant species
commonly occurring together tend to have
similar scores and those rarely found together
are characterised by dissimilar scores, the
aggregations of quadrats (arranged as they
are by their species composition) produce
ecologically meaningful aggregations when
the ordination is plotted in two-dimensional
space. The software also offers the
possibilities to plot individual species
according to their overall scores on the first
two axes to help guide interpretation of the
plant communities. We crudely categorised
the clusters of quadrats subjectively by their
dominant species to describe the types of
vegetation present in each, and we compared
those quadrats which fell within the
minimum convex polygons used by the
radio-tracked crakes with those that did not,
in an attempt to assess the degree of habitat
selection within the vegetation types present
in the three management units.
Results
Mapping territorial singing birds
Mapping of Spotted Crake took place on 16
nights between 16 April and 9 July, when
0–6 individuals were registered singing
within a minimum of nine discrete areas
(Figs. 1 and 2). The central positions of all
recorded singing Spotted Crakes at Lille
Vildmose are shown in Fig. 1. Spotted
crakes were only heard singing consistently
in the drier less ridged areas of the narrow
deep extraction pits, not associated with
deep water (in restricted parts of area 3) and
in the very flat restored areas either
supporting sedge meadow, reeds and carr
(area 5) or acidic wet grassland, reeds and
Reedmace
Typha latifolia
(area 8). Birds were
