Download The relevance of non-farmland habitats, uncropped areas and

Ibis (2004), 146 (Suppl. 2), 22– 31
The relevance of non-farmland habitats, uncropped
areas and habitat diversity to the conservation of
farmland birds
Blackwell Publishing, Ltd.
R. J. FULLER, 1* S. A. HINSLEY 2 & R. D. SWETNAM 2
British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU, UK
2
Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE28 2LS, UK
1
Use of non-farmland habitats by species generally perceived as ‘farmland birds’ is common,
yet these habitats are not always considered in conservation strategies aimed at population
recovery. At the national scale, many farmland species occur in landscapes not dominated
by farmland. An analysis of distribution atlas data coupled with remotely sensed habitat data
showed that for 16 out of 28 farmland species, less than half of the breeding range was associated with high cover of lowland farmland. However, with a few exceptions, populations
breeding in non-farmland habitats are likely to depend on farmland at some time in the year.
Within farmland landscapes, uncropped areas and patches of non-farmland habitat can
provide nesting, foraging or roosting resources. Habitats that are scarce on farmland and that
provide potential supplementary or complementary resources to those available within the
productive areas of farmland include ruderal vegetation, rough grassland and scrub. Enhancing habitat diversity through provision of modest quantities of these habitats will benefit
farmland birds. Complete knowledge of year-round habitat requirements and patterns of
resource use at all scales is needed if robust national conservation plans are to be developed
for farmland species. Similarly, interactions between the farmland and non-farmland sections of populations need to be determined.
Agricultural intensification has reduced habitat
heterogeneity at all scales within farmed landscapes
with detrimental effects on biodiversity (Benton et al.
2003). More specifically, there is substantial evidence that specific changes in farming practices have
been principal drivers of declines in farmland birds
through effects on food resources and habitat quality
(Chamberlain et al. 2000, Fuller 2000). Uncropped
areas provide important resources for birds and
other wildlife within farmed landscapes yet, with the
exception of hedgerows (Hinsley & Bellamy 2000)
and field margins (Vickery et al. 2002), relatively little attention has been paid to the implications of
reduction in their diversity, quantity and quality.
It has become conventional to regard ‘farmland
birds’ as species that depend largely on lowland fields
or field margins for their food (Gibbons et al. 1993,
Fuller et al. 1995). This approach has been useful in
helping to focus research on species most seriously
*Corresponding author.
Email: [email protected]
© 2004 British Ornithologists’ Union
affected by agricultural practices and in formulating
the UK Government’s ‘Farmland Bird Index’ (FBI),
which measures the general health of farmland
bird populations in Britain (www.sustainabledevelopment.gov.uk, Gregory et al. 2004). However,
classification of species by general habitat associations is not straightforward and can be potentially
misleading. The cues by which birds select their habitat (Hildén 1965, Wiens 1989) are very different to
the criteria typically used by ecologists to define
spatial variation in the environment. Many species use
more than one broad habitat (defined as farmland,
woodland, moorland, scrub, etc.). Their distribution
across such habitats may vary in time depending on
population level (Wiens 1989). Even where species
appear to occupy mainly one habitat in one season,
they may depend on another in other seasons, or they
may require a combination of habitats within a season.
The use of non-farmland habitats can be viewed
on a continuum of scales. At one extreme is the situation in which populations of farmland birds occur
in habitats that do not form an intimate part of the
Non-farmland habitats, uncropped areas and habitat diversity
farmed landscape. In some cases, individuals within
these populations may be functionally isolated
from farmland for a part of the year, especially in the
breeding season. At the other extreme, within many
agricultural landscapes, populations of farmland
birds may use a complex of landscape elements
comprising both uncropped and cropped areas. This
paper takes a dual-scale view of habitat use by farmland birds in an attempt to assess the ecological
significance of habitats that do not form a part of
productive agricultural systems. First, broad habitat
associations are examined at the national (i.e.
British) scale. We ask to what extent the national distributions of farmland birds actually coincide with
farmland and we review the use made by farmland
birds of non-farmland habitat in Britain. Secondly,
at a finer scale, the use made of non-farmland and
uncropped habitats within farmed landscapes is
reviewed and we summarize the availability of such
habitats at this scale.
DEFINITIONS AND METHODS
We treated ‘farmland species’ as the 28 species
classified by Gibbons et al. (1993) as farmland birds
(Table 1). In its broadest sense, farmland in Britain
embraces extensively grazed unenclosed grassland
and moorland in the uplands as well as more intensively managed land in the lowlands. However, our
definition of farmland is essentially a lowland one
because we believe the term ‘farmland bird’ has
become synonymous with the lowlands. Farmland
habitats were broadly taken as all tilled land and all
grassland excluding moorland grass. Non-farmland
included woodland, scrub, saltmarsh, dune and shingle systems, fens and swamps, unimproved upland
margins, upland grass, dwarf shrub heath, moorland,
gardens and urban areas. When considering fine-scale
habitat use within farmland, we considered nonfarmed habitats as all uncropped and infrequently
managed areas, including rough grassland and the
immediate vicinity of farmsteads. Cropped areas are
defined as all productively managed arable land and
grassland. We do not review the use of hedgerows or
set-aside by birds because the resources they provide
for farmland birds have been relatively well documented
(Henderson & Evans 2000, Hinsley & Bellamy 2000).
The Centre for Ecology and Hydrology’s Land
Cover Map 1990 (LCM) (Fuller et al. 1994) was
used in conjunction with BTO data from the
1988–91 breeding bird atlas (Gibbons et al. 1993) to
examine distributions of farmland birds at the
23
national scale within mainland Britain. These two
contemporary data sets allow comparisons that were
applicable in 1990; it should be noted that several of
the species have shown subsequent changes in range.
The LCM allows the whole of Britain to be allocated
to 25 land cover classes. Lowland farmland was
defined as comprising the following five land cover
classes: class 5 – lowland grass heath; class 6 – pasture/
amenity turf; class 7 – meadow/verge/semi-natural
swards; class 8 – rough grass/marsh grass; class 18 –
tilled land. This definition of farmland includes some
classes that are likely to include some unimproved
rough grassland. The areas of each of these classes
were summed to estimate the total area of farmland
in each 10-km square of the Ordnance Survey
National Grid.
For each species in turn, the proportion of the
total number of squares in which each was recorded
as breeding was calculated for three categories of
cover of farmland (0–30%, 31–70%, > 70%) and compared with the proportions for mainland Britain as a
whole. These ‘all-squares’ analyses were repeated
for a subset of 10-km squares where each species
was likely to be most abundant. In the atlas, ‘relative
abundance’ within each 10-km square was estimated
from the proportion of tetrads (2-km squares) in
which each species was recorded. Those 10-km
squares in which a minimum of eight tetrads had
been surveyed and in which the proportion of tetrads with breeding confirmed for the particular
species was ≥ 0.4 were selected and are termed ‘high
abundance squares’. This analysis was conducted for
21 farmland species; there were insufficient data for
the remaining seven species. To determine which
non-farmland land cover classes were most frequent
in squares occupied by each species, mean percentages of each of the 25 land classes were calculated for
each occupied 10-km square and then grouped into
broad habitat types. Types and quantities of nonfarmland and uncropped habitats within farmland
were summarized from LCM 1990 for six English
counties (mainly arable – Cambridgeshire, Lincolnshire and Essex; mainly grassland – Devon, Somerset
and Dorset).
RESULTS AND DISCUSSION
Distribution of farmland birds with
respect to landscape type
In Table 1a, the species are listed in approximate
decreasing order of apparent dependence on farmland
© 2004 British Ornithologists’ Union, Ibis, 146 (Suppl. 2), 22– 31
24
R. J. Fuller, S. A. Hinsley & R. D. Swetnam
Table 1. Distribution of species perceived as farmland birds in relation to farmland landscapes in Britain. Proportion of occupied 10-km
squares is shown for landscapes containing different proportions of farmland where (a) is all squares with the species and (b) are those
squares containing the highest relative abundance of the species. Farmland habitats were defined using data from the CEH Land Cover
Map 1990 and data on bird ranges was drawn from the BTO 1988–91 Breeding Bird Atlas (see Methods). For seven species (indicated
by –), the data were insufficient to calculate an index of abundance; data were also unavailable for Woodpigeon (indicated by *). Species
included in the Farmland Bird Index are shown in italics. n = number of 10-km squares occupied. Chi-square tests and P-values compare
the observed distributions across the three landscape types with those evident for the whole of Britain.
Proportion of farmland in mainland Britain according to the percentage of farmland per 10-km square
≤ 30% 31–70% > 70%
≤ 30% 31–70% > 70%
0.33
(a)
n
Stone Curlew
Quail
Turtle Dove
Red-legged Partridge
Hobby
Corn Bunting
Yellow Wagtail
Tree Sparrow
Little Owl
Yellowhammer
Stock Dove
Grey Partridge
Rook
Barn Owl
Whitethroat
Goldfinch
Linnet
Greenfinch
Jackdaw
Montagu’s Harrier
Reed Bunting
Kestrel
Starling
Lapwing
Skylark
Woodpigeon
Cirl Bunting
Corncrake
44
233
700
894
230
686
759
1040
942
1962
1423
1278
1954
748
1934
1888
2002
2056
2149
5
1846
1992
2498
2091
2571
2308
18
105
0.00
0.06
0.04
0.08
0.04
0.11
0.08
0.07
0.08
0.12
0.11
0.13
0.17
0.15
0.21
0.18
0.21
0.22
0.23
0.00
0.25
0.27
0.31
0.31
0.35
0.37
0.39
0.79
0.22
0.45
Proportion of
breeding range
0.11
0.25
0.28
0.28
0.33
0.27
0.31
0.34
0.36
0.35
0.37
0.35
0.38
0.40
0.35
0.37
0.36
0.35
0.36
0.60
0.34
0.34
0.32
0.33
0.30
0.34
0.33
0.14
0.89
0.69
0.67
0.64
0.63
0.62
0.61
0.59
0.56
0.53
0.52
0.51
0.46
0.45
0.45
0.44
0.43
0.43
0.41
0.40
0.40
0.39
0.37
0.36
0.35
0.29
0.28
0.07
0.33
χ2
P
(b)
n
22.8
57.9
189.1
173.5
64.5
96.4
146.4
213.7
183.3
257.1
214.2
151.6
180.0
88.1
107.6
153.3
125.6
110.9
112.3
–
70.4
69.6
67.1
69.9
71.0
149.5
1.71
50.8
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
–
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
0.557
< 0.001
–
–
338
385
–
161
208
188
–
1663
672
54
1641
10
1215
1098
429
1550
1716
–
473
182
2431
344
2171
*
–
–
–
–
0.02
0.03
–
0.07
0.04
0.01
–
0.05
0.07
0.04
0.05
0.10
0.08
0.05
0.08
0.07
0.07
–
0.13
0.07
0.10
0.09
0.16
*
–
–
0.22
0.45
Proportion of
breeding range
–
–
0.22
0.20
–
0.28
0.24
0.24
–
0.36
0.39
0.39
0.40
0.60
0.38
0.41
0.40
0.40
0.44
–
0.42
0.48
0.42
0.44
0.40
*
–
–
–
–
0.75
0.77
–
0.65
0.72
0.75
–
0.59
0.55
0.57
0.55
0.30
0.55
0.53
0.52
0.54
0.48
–
0.45
0.45
0.48
0.47
0.45
*
–
–
χ2
P
–
–
118.3
127.8
–
35.0
61.3
70.3
–
431.3
152.4
16.1
441.3
–
249.7
295.7
91.3
355.1
417.0
–
71.4
47.7
453.2
72.4
241.0
*
–
–
–
–
< 0.001
< 0.001
–
< 0.001
< 0.001
< 0.001
–
< 0.001
< 0.001
< 0.001
< 0.001
–
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
–
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
*
–
–
Scientific names: Stone Curlew Burhinus oedicnemus, Quail Coturnix coturnix, Turtle Dove Streptopelia turtur, Red-legged Partridge
Alectoris rufa, Hobby Falco subbuteo, Corn Bunting Emberiza calandra, Yellow Wagtail Motacilla flava, Tree Sparrow Passer montanus,
Little Owl Athene noctua, Yellowhammer Emberiza citrinella, Stock Dove Columba oenas, Grey Partridge Perdix perdix, Rook Corvus
frugilegus, Barn Owl Tyto alba, Whitethroat Sylvia communis, Goldfinch Carduelis carduelis, Linnet Carduelis cannabina, Greenfinch
Carduelis chloris, Jackdaw Corvus monedula, Montagu’s Harrier Circus pygargus, Reed Bunting Emberiza schoeniclus, Kestrel Falco
tinnunculus, Starling Sturnus vulgaris, Lapwing Vanellus vanellus, Skylark Alauda arvensis, Woodpigeon Columba palumbus, Cirl
Bunting Emberiza cirlus, Corncrake Crex crex.
based on the ‘all-squares’ analysis. Thus species such
as Stone Curlew (scientific names are given in Table 1),
Quail and Turtle Dove are highly associated with
farmland landscapes, being present in a relatively
low proportion of squares with < 30% farmland, but
in a relatively high proportion of squares with >70%
farmland. In contrast, species such as Starling,
© 2004 British Ornithologists’ Union, Ibis, 146 (Suppl. 2), 22–31
Lapwing and Skylark have distributions suggesting a
wider use of habitat types. For 16 out of 28 species,
less than half of the breeding range was associated
with squares with high cover of lowland farmland.
This included diverse species such as Barn Owl, Linnet,
Reed Bunting, Lapwing and Skylark. The apparently
high dependency of Corncrake and Cirl Bunting on
Non-farmland habitats, uncropped areas and habitat diversity
25
Table 2. Major habitat types (≥ 4% mean cover) within the breeding ranges of farmland birds. Figures are mean percentage cover per
occupied 10-km square drawn from the BTO 1988–91 Breeding Bird Atlas calculated for broad habitat types defined from the CEH Land
Cover Map 1990 (see Methods). Broad habitats are defined using the following amalgamations of LCM1990 land cover classes: Coastal
= classes 1 and 3; Woodland = 15 and 16, Rural /suburban development and urban = 20 and 21; Moorland = 9 and 10. Values of < 4%
are indicated by –.
Species
Stone Curlew
Turtle Dove
Hobby
Red-legged Partridge
Quail
Yellow Wagtail
Tree Sparrow
Little Owl
Corn Bunting
Stock Dove
Yellowhammer
Grey Partridge
Montagu’s Harrier
Barn Owl
Rook
Goldfinch
Whitethroat
Greenfinch
Linnet
Jackdaw
Reed Bunting
Kestrel
Lapwing
Starling
Skylark
Wood Pigeon
Cirl Bunting
Corncrake
Farmland
Coastal
Woodland
Rural /suburban
development
and urban
77
72
70
70
70
68
68
67
67
64
64
62
61
60
59
58
57
56
56
55
54
52
50
50
47
44
42
20
–
5
–
6
7
5
7
6
11
7
10
8
20
10
10
11
13
12
13
12
12
10
13
16
16
13
44
46
7
6
8
5
5
4
5
6
4
6
6
5
5
6
5
5
5
5
5
5
5
5
4
4
4
8
–
–
5
9
11
8
6
9
8
8
8
7
7
7
6
5
6
6
6
6
6
6
6
6
5
5
5
4
4
–
non-farmland squares was an artefact due to the concentration of these localized species in areas where
the squares tended to be classified in coastal land
classes. Differences between the proportions of species’ ranges in each of the farmland categories and
those of farmland in mainland Britain as a whole
were significant (P < 0.001, χ2 tests) for all species
except Cirl Bunting, but given the generally large
sample sizes (except Montagu’s Harrier, sample size
too small to test) this was not unexpected.
Repeating the analysis for the ‘high abundance
squares’ (Table 1b) produced a similar pattern to
that for ‘all squares’. With the exception of Barn
Owl, these ‘high abundance squares’ were more
strongly dominated by lowland farmland than was
the case for all occupied squares. Nonetheless, for
seven out of 20 species less than half of the ‘high
Moorland
0
–
–
–
–
–
–
–
–
–
–
–
0
–
–
–
–
4
–
10
9
12
12
4
13
17
–
16
abundance squares’ contained > 70% farmland. The
differences between bird and farmland distributions
were all significant (P < 0.001, χ2 tests).
The mean habitat composition of all occupied
squares is shown in Table 2 by broad habitat groupings. Species are listed in decreasing order of the
percentage cover of farmland within the breeding
range and they show a similar order to that evident
using the approach in Table 1. Four non-farmland
habitat types emerged as potentially important
for farmland birds (Table 2). For many species, the
occupied squares contained on average > 10% of
coastal habitats. Woodland and suburban/built-up
areas also featured regularly. Mean cover of moorland was relatively high (> 10%) in squares occupied
by Jackdaw, Kestrel, Lapwing, Skylark, Woodpigeon
and Corncrake.
© 2004 British Ornithologists’ Union, Ibis, 146 (Suppl. 2), 22– 31
26
R. J. Fuller, S. A. Hinsley & R. D. Swetnam
Table 3. Examples of farmland species widely associated with non-farmland habitats.
Breeding season
Upland heath & moorb
Upland marginsb
Lowland heathc
Ruderal areasd
Scrube
Young plantationsf
Gardensg
Saltmarshh
Dune systemsi
Coastal grazing marshj
Outside breeding season
KestrelNF, SkylarkNF
KestrelNF, Grey PartridgeNF, LapwingNF, SkylarkNF,
JackdawF, RookF, StarlingF, LinnetNF,
YellowhammerNF
KestrelNF, SkylarkNF, WhitethroatNF, LinnetNF,
YellowhammerNF, Reed BuntingNF
SkylarkF, WhitethroatNF, GreenfinchF, GoldfinchF,
LinnetF, YellowhammerF, Reed BuntingF,
Corn BuntingF
WoodpigeonNF, Turtle DoveN, WhitethroatNF,
GreenfinchN, LinnetN, YellowhammerNF
KestrelF, WoodpigeonNF, Turtle DoveN, SkylarkNF,
WhitethroatNF, LinnetN, YellowhammerNF
WoodpigeonNF, JackdawNF, StarlingF,
GreenfinchNF, GoldfinchNF
KestrelF, Grey PartridgeNF, LapwingNF, SkylarkNF,
Yellow WagtailNF, LinnetNF,
Reed BuntingNF
KestrelF, WoodpigeonNF, Turtle DoveNF, SkylarkNF,
WhitethroatNF, LinnetNF, YellowhammerNF,
Reed BuntingNF
KestrelF, Grey PartridgeNF, LapwingNF, SkylarkNF,
Yellow WagtailNF, StarlingF
KestrelF, JackdawF, RookF, StarlingF
Tree SparrowF, GreenfinchF, GoldfinchF,
LinnetF, YellowhammerF, Reed BuntingF,
Corn BuntingF
WoodpigeonR, StarlingR, Tree SparrowR,
GreenfinchR, GoldfinchR, LinnetR,
YellowhammerR, Reed BuntingR,
Corn BuntingR
(thicket stage may hold roosts similar to scrub)
StarlingF, GreenfinchF, GoldfinchF
KestrelF, LapwingF, SkylarkF, JackdawF,
RookF, GreenfinchF, GoldfinchF, LinnetF,
Reed BuntingF
Dune scrub probably used as roost by
finches and buntings
LapwingF, StarlingF
N
Nests, Ffeeds, Rroosts in the habitata. Note that the list of habitats and species is not comprehensive and that only FBI species are
considered (see Table 1).
a
General sources: Fuller (1982), Cramp et al. (1979 –1994).
b
Upland heath and moor are unenclosed rough grazing land in north and west Britain, typically dominated by Calluna vulgaris, Molinia
caerulea, Nardus stricta and other grasses. Upland margins includes unimproved enclosed land just below the open moors often
consisting of rough grazing with extensive Pteridium aquilinum in some regions, notably in Wales. Sources: Ratcliffe (1990), Fuller et al.
(2002), Milsom et al. (2002).
c
Typically dominated by Calluna vulgaris and Ulex spp. Most farmland birds are associated with scrub on heathland. Source: Bibby
(1978).
d
Vegetation in ruderal areas consists of weedy species (e.g. grasses, thistles, Chenopodium spp., Rumex spp., Urtica spp., Epilobium
spp.) typically found on waste land or uncultivated, but episodically cleared or disturbed, areas such as around farm buildings and on
rough ground alongside streams, in field corners, etc. If left indefinitely it may develop into scrub.
e
Scrub occurs in many forms; here it refers to successional development of woody vegetation (both open- and closed-canopy) on
abandoned or marginal land in the lowlands. Sources: Fuller (1995), Gough (1999).
f
Includes recently established farm woods (Vanhinsbergh et al. 2002) and establishment and thicket-stage conifer plantations (Fuller &
Browne 2003).
g
Rural gardens can attract a wide range of farmland species in winter but the three listed are those that most widely occur in gardens.
Source: Bland et al. (2004).
h
Sources: Morgan (1978), Brown and Atkinson (1996), Ferns (1992).
i
With the exception of Skylark, which reaches high densities in some dune systems, nesting farmland birds are largely confined to areas
of scrub within dunes. Sources: Delius (1965), Morgan (1978), Ferns (1992).
j
Sources: Milsom et al. (1998, 2000, 2001).
Patterns of large-scale use of nonfarmland habitats
Using data at a national scale from a large sample of
randomly distributed transect plots, Gregory and
Baillie (1998) estimated broad habitat distributions
for eight breeding species, four of which are farmland
© 2004 British Ornithologists’ Union, Ibis, 146 (Suppl. 2), 22–31
birds. In all cases, a substantial proportion of birds
was associated with non-farmland habitats: Skylark 42%, Starling 65%, Linnet 32%, Reed Bunting
49%. The functional significance of different habitats
was unclear from these data, but in Table 3 we
summarize the uses that farmland birds make of
some non-farmland habitats. These results, derived
Non-farmland habitats, uncropped areas and habitat diversity
independently, are consistent with the findings in
Tables 1 and 2.
Certain habitats can be singled out as especially
significant at a national scale. The uplands hold
> 30% of the British breeding population of Skylarks
(Chamberlain & Gregory 1999, Browne et al. 2000)
with the highest densities on semi-natural grass
(Brown & Stillman 1993, Chamberlain & Gregory
1999). Some of the highest concentrations of breeding Lapwings in England and Wales occur on the
upland fringes and > 25% of pairs in 1998 were
estimated to be on rough grassland, much of it presumably in the upland margins (Wilson et al. 2001).
Nearly 50% of the Starling population may be
associated with urban areas (Gregory & Baillie
1998) while gardens are also especially important
for Greenfinch and Goldfinch (Bland et al. 2004).
Young conifer plantations provide breeding habitat
for large numbers of Yellowhammers. Coastal populations of breeding Skylarks and Lapwings are likely
to be considerable. Almost any habitats with scrub
will support Whitethroats, Linnets and Yellowhammers – this applies to dune systems, lowland heaths,
commonland, downland, marginal uplands and the
upper slopes of coastal cliffs. Outside the breeding
season, concentrations of farmland passerines are
found in gardens and saltmarshes while all habitats
containing scrub are potentially roosts for finches,
buntings, sparrows and Starlings. In a national survey
of wintering Skylarks, the highest densities were
found on saltmarsh, although the bulk of the population was on farmland (Gillings & Fuller 2001).
Habitat use within farmed landscapes
Where farming is the dominant land-use, lowland
landscapes are generally patchy mosaics consisting of
fields, hedges, farmsteads, woods, patches of scrub,
streams and other wetlands. In our six sample counties, woodland and suburban/built-up areas provided
the most extensive non-farmland habitats, ranging
from 1 to 11% cover and 3 to 13% cover, respectively,
across the six counties. Three structural aspects of
habitat composition seem especially important in
shaping the make-up of breeding bird communities
on farmland: the extent of woodland, the density of
hedgerows and the density of wetlands (streams and
ponds) (Fuller et al. 1997). Within farmland, Grey
Partridge, Lapwing, Skylark and Yellow Wagtail are
strongly associated with cropped areas, but all the
other FBI species are likely to make some use of
uncropped areas.
27
Woodland is used by several farmland birds in the
breeding season both for nesting and for feeding.
This is especially true of young plantations (Table 3).
However, more mature woods can also be used by
Woodpigeon, Stock Dove, Turtle Dove, Greenfinch,
Goldfinch and Yellowhammer. The last four species
tend to be associated with the edges of mature woodland, probably because they depend on habitats
outside woodland for food and their occurrence in
woodland can be influenced by the proximity of food
sources (Hinsley et al. 1995). However, Whitethroat,
Linnet, Goldfinch, Greenfinch and Yellowhammer
all show stronger association with hedgerows than
with woodland (Fuller et al. 2001). Similarly, scrub
is probably more important for farmland birds than
woodland. Scrub is strongly selected as a nesting
habitat by Turtle Doves (Browne & Aebischer 2004)
and as a roosting habitat, especially by finches and
buntings (Table 3).
An increasing number of studies have examined in
detail how farmland birds utilize the habitat features
available within farmed landscapes. Some of these
show that particular habitats may provide essential
feeding areas: for example, patches of rough grassland in the case of Skylark (Wilson 2001), Yellowhammer (Bradbury et al. 2000 and references therein)
and Corn Bunting (Watson & Rae 1997), rank vegetation for Reed Bunting (Brickle & Peach 2004) and
wet or emergent areas for Tree Sparrow (Field &
Anderson 2004) and Reed Bunting (Brickle & Peach
2004). Corn Buntings in the Outer Hebrides make
much use of uncultivated areas both for nesting and
for feeding (Hartley & Shepherd 1997). Although
technically not a farmland bird in the context of this
paper, it is also worth noting that Song Thrushes Turdus
philomelos on farmland depend strongly on uncropped
habitats, including woodland edges, scrub, field
boundaries and gardens (Peach et al. 2004). Ruderal
vegetation can provide important localized feeding
sites for birds both in summer and in winter, for both
insectivorous and granivorous species (Table 3). Constituents of ruderal vegetation providing food sources
for granivorous birds are Polygonaceae, Chenopodiaceae and Asteraceae (Wilson et al. 1999). These
resources can occur in a variety of situations such as
neglected land in the vicinity of farm buildings and
the vegetation along linear wetlands and around ponds.
A process-based perspective
Dunning et al. (1992) provided a useful framework
for discussing how the cropped and non-cropped
© 2004 British Ornithologists’ Union, Ibis, 146 (Suppl. 2), 22– 31
28
R. J. Fuller, S. A. Hinsley & R. D. Swetnam
components of landscapes may interact with population dynamics. They identified two processes involving the movement of individuals between patches
to exploit resources. ‘Landscape complementation’
occurs where a species requires at least two different
resources (equivalent here to habitats) within the
same season. This requires that the resources are
available in reasonably close proximity (Eybert et al.
1995). Seed-eating birds provide striking examples
of this process. Turtle Doves depend on scrub,
hedgerows and woodland edges as nesting habitat,
although they forage on spilt grain and on seedrich patches in fields and ruderal areas (Browne &
Aebischer 2004). In winter, several seed-eaters roost
in scrub, but forage in other patch types. ‘Landscape
supplementation’ applies to situations where different habitats offer substitutable resources. An example is the use of ruderal areas as seed sources to
supplement those available in fields and field margins. It is likely that ruderal areas have increased in
relative importance as seed supplies in arable fields
have become depleted in recent decades. Similarly,
ruderal and other non-crop patches may provide
resources at critical periods, for example in late winter/early spring when food supplies in fields may be
exhausted. In summer, such substitutable resources
would need to be in relatively close proximity, but in
winter birds could potentially exploit substitutable
resources on a larger scale, possibly showing seasonal
shifts in the types of habitats used.
Source-sink dynamics form a third process
whereby individuals in a population occupy habitats
differing in quality (Dunning et al. 1992, Watkinson
& Sutherland 1995). The consequence may be that
poor-quality habitats could be sinks where occupancy is only sustained by immigration from highquality source habitats where breeding production
generates a surplus. To our knowledge, such effects
have not been demonstrated for any farmland species, although they may occur across a variety of
scales including regions and broad farming systems
that vary in habitat quality (Wilson & Griffiths 1997)
and more locally where potentially productive habitats exist close to unproductive ones. Given the poor
performance of some species on farmland, the possibility exists that farmland habitats could constitute
sink habitat on a large scale. Thus the ‘true’ status of
farmland populations could be worse than apparent
if numbers are being buffered by immigration from
non-farmland source populations.
It is very likely that breeding output of some species is now higher in non-farmland habitats than in
© 2004 British Ornithologists’ Union, Ibis, 146 (Suppl. 2), 22–31
intensively farmed areas. Lapwings and Skylarks, for
instance, may achieve higher productivity in some
upland and saltmarsh habitats than in many areas of
intensively managed lowland farmland. Sustained
high breeding output in non-crop habitats does
not, however, guarantee that populations in these
habitats are buffered against change. Such buffering
would depend in part on the distribution of the surplus between source and sink type habitats. In addition, at other times of year, a high proportion of the
population may depend on lowland farmland where
food supplies have been reduced. This may account
for declines in upland and dune-nesting Skylark
populations (Chamberlain 2001, Wolfenden & Peach
2001).
The extent and type of non-crop habitat in farmland landscapes almost certainly affects predation
risk, although knowledge of the impact of predation
at the population level is lacking. Generalist predators can attain high numbers in farmland mosaics
and may be particularly effective at exploiting prey
restricted to edges and patches of fragmented habitat. Little is known about relationships between
landscape structure and breeding success in opencountry species. It is clear, however, that some
farmland birds avoid even lightly wooded areas
(e.g. Hancock & Wilson 2003). The balance of
cropped and non-cropped areas within farmland
landscapes has a major effect on composition of bird
communities (Fuller et al. 1997). This raises the possibility of interspecific competition for food resources
varying according to landscape structure and habitat
composition. For example, landscapes with a combination of woodland and rape crops generally support
high numbers of Woodpigeons, which may compete
at certain times of year with other granivores. It is
also possible that species principally associated with
woodland or scrub may compete with farmland
birds for food in ruderal habitats. Thus non-cropped
land within farmland has both positive and negative
aspects.
CONCLUSIONS
Non-farmland habitats appear to support substantial
proportions of the British breeding populations of
several farmland birds. However, few of these nonfarmland populations are isolated from farmland
because (a) individuals breeding in non-farmland
habitats may feed on farmland in summer and
(b) many birds may depend on farmland outside the
breeding season. The main exceptions are populations
Non-farmland habitats, uncropped areas and habitat diversity
of Whitethroats that nest and feed within scrub and
young woodland, and populations of Goldfinches,
Greenfinches and Starlings associated with urban
areas. Knowledge of the large-scale population structure with respect to interaction between farmland
and non-farmland habitats is completely lacking.
Within farmland landscapes many species use a
variety of habitats for different purposes, but
detailed knowledge of habitat use is incomplete for
most species. There is a need to study year-round
ranging behaviour of farmland birds to ascertain
more exactly the spatial, temporal and diurnal use of
both cropped and non-cropped habitats, and to
investigate the characteristics of movements between
farmland and non-farmland sections of their populations. Many studies of foraging habitat requirements
have focused on the use of fields by birds (for an
exception see Hancock & Wilson 2003), but these
do not give comprehensive information on resource
use. A better understanding of ‘whole landscape use’
is needed for most species.
Some of the uncropped habitats that appear to
provide roosting and foraging habitats for some species are rare in farmed landscapes. Rough grassland,
ruderal vegetation and scrub are examples. LCM 1990
data indicate that these three habitats seldom contribute more than 1% of the land cover within farmed
counties and are absent from substantial tracts of
farmland. Cropped areas undoubtedly provide the
major food resources for many farmland birds, especially in winter (e.g. Hancock & Wilson 2003). However, uncropped areas and non-farmland habitats
potentially offer supplementary food resources and,
in some landscapes, these may even become critical
at certain times of year and help to buffer populations against negative environmental change. We
contend that enhancing the diversity of habitat within
farmland landscapes through modest increases in the
extent of these habitats could benefit many farmland
birds, as well as bringing wider biodiversity gains.
Examples of this type of integrated approach to conservation within farmed landscapes are to be found
in Germany (Berger et al. 2003) but are currently
sparse in Britain. The introduction of the Environmental Stewardship scheme in 2005 in England,
along with similar schemes in Scotland and Wales,
offers an opportunity to move further in this direction (Smallshire et al. 2004; Vickery et al. 2004).
R.J.F.’s work on this paper was funded through a partnership between the British Trust for Ornithology and the
Joint Nature Conservation Committee (on behalf of
29
Scottish Natural Heritage, English Nature, the Countryside
Council for Wales and the Environment & Heritage Service of Northern Ireland). We acknowledge the huge efforts
of those who contributed to the 1988–91 breeding bird
atlas and we thank Nicki Read for help in preparing this
paper.
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