Conservation Science in the RSPB 2006

32
Yellow wagtails breeding
on arable farmland
The UK’s near-endemic race of the
yellow wagtail (flavissima) has
declined strongly in grassland
regions, and the bulk of the
population now breeds on arable
land in eastern England. It now
qualifies for red-listing as a species
of conservation concern, because
of its large population decline in
the last three decades. As part of a
wider study of yellow wagtails, the
RSPB and its partners funded a
PhD project to understand the
species’ ecology on arable land,
and to identify possible
conservation measures.
The student, James Gilroy, found
that, in areas dominated by winter
cereals, as crop height and density
increased, nesting activity declined
rapidly by late June. Birds moved into
more open spring-sown potato crops
for second or replacement clutches,
and nesting activity in these crops
remained high until late July. Even for
early nests in cereals, tall dense
vegetation forced many birds to nest
close to ‘tram-lines’ in the crop,
where (as with skylarks) they suffered
higher predation rates. Nests in
another favoured crop, field beans,
suffered very high predation rates. As
bean crops develop, the crop
understorey becomes very open,
meaning that nests that were initially
well hidden became more visible
and vulnerable.
In addition to these crop type effects,
there was a strong effect of soil type
on the density of yellow wagtail
territories. Softer and more penetrable
soils, such as peat, were associated
with higher territory densities. The
reason is unclear, but may relate to
the greater organic matter content of
such soils being associated with
higher populations of invertebrates
with a soil-dwelling life-stage.
Future work is planned to determine
whether small unplanted patches, as
now used for skylarks, create any
benefit for wagtails nesting in cereals;
the best way to create late-season
nesting habitat in areas currently
lacking suitable crop types; and what
links soil type with territory density.
Contact:
guy.anderson@rspb.org.uk
This research is part of a collaboration between
the RSPB, the University of East Anglia, English
Nature (as part of the Action for Birds in England
partnership), the British Trust for Ornithology,
Anglian Water and Mr Nicholas Watts.
See also: 2001: 18; 2004: 31;
2005: 47
Left: A predated yellow wagtail nest
in field beans. The open understorey
of the mature crop may make nests
more visible and vulnerable.
Seasonal pattern of nest density of yellow wagtails in arable crops.
Approximately weekly data shown separately for six regularly
monitored areas in Cambridgeshire and Lincolnshire Fens. Areas
with potatoes supported active nests for longer than those without.
James Gilroy (UEA)
Nest density (Active Nests km -2 )
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Sites with potato fields
Sites without potato fields
3 4 1 2 3 4 1 2 3 4 1 2
May June July August
Week