120 Spotted Crake habitat use
©Wildfowl & Wetlands Trust
Wildfowl
(2013) 63: 115–134
on a total of 18 days between 31 May and 16
August 2013. The bearings of the strongest
directional signal were taken using a
compass in the field, each from at least three
positions located using a Garmin eTrex
GPS, and the position of the bird drawn
relative to the resulting triangulation. Most
of the positions were generated from a
single occasion on each date, to maximise
the independence of observations from
those on earlier and subsequent days, but on
the few occasions more than one fix was
obtained during a field visit, these were
taken at intervals of > 90 min. Minimum
convex polygons were calculated for each
bird based on the cumulative positions
generated for each individual using Ranges 8
v2.13 (Kenward
et al.
2008).
Permission to catch Spotted Crakes was
sought in areas of the restoration project
where the species was known to occur, but
where catching activities were not likely to
conflict with the nature conservation
management objectives of the site (
e.g
. by
disturbing other rare breeding species), or
damage other features of the wetlands. In
the event, birds were caught at three sites
(each representing a separate management
unit) in two areas. The first site was east of
the Grønvej gravel track, in an old ditch line
overgrown with Common Reeds
Phragmites
australis
and willow scrub, mainly Grey
Willow
Salix cinerea
, but with some Bay
Willow
S. pentandra
; the second was south
and west of this in a flat open expanse of
what was bare peat in 2009, recently
rewetted by using bunding and ditch
blocking to raise water levels and stimulate
re-growth of wetland vegetation; the third
catch site was north of the Hegnvej gravel
track and north of an abandoned narrow
gauge railway track in another area of ridged
former peat cuttings recolonised with
extensive
Phragmites
and
Salix
scrub, but
with abundant Common Cotton Grass
Eriophorum angustifolium
in the understorey
(more typical of mire vegetation and largely
absent at the other two catch sites, which
appeared more mineral-enriched).
Vegetation sampling
Plant species percentage cover for different
types of vegetation was recorded in 139
quadrats (1 m × 1 m) within the three areas
where we tagged crakes: 36 in Territory 1
(17 June), 51 in Territory 2 (18 June) and 52
in Territory 3 (20 June). Because of the
complex nature of the vegetation, we
quickly abandoned random sampling,
because this over-represented the drier
habitats within the management units that
were rarely used by crakes. Instead, we
attempted to sample representative
vegetation types that reflected the extent
and variability of the vegetation stands
present in each area. While this was not an
objective method of describing the
vegetation, it did ensure that within each
management unit, the full range of
vegetation types and gradients between
typical associations were represented when
comparing vegetation present at the site to
those types present where the crakes were
triangulated. Vegetation height for each
quadrat was measured as the mean height
(cm from water level/substrate surface) of
five random measurements taken within
each quadrat. Where water was present,
mean, minimum and maximum depths (cm)
were calculated from 10 random depth
