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Ibis (2004), 146, 579– 600
Review paper
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The recent declines of farmland bird populations
in Britain: an appraisal of causal factors and
conservation actions
IAN NEWTON*
Centre for Ecology and Hydrology, Monks Wood Research Station, Abbots Ripton, Huntingdon, Cambs. PE28 2LS, UK
In this paper, the main aspects of agricultural intensification that have led to population declines
in farmland birds over the past 50 years are reviewed, together with the current state of knowledge, and the effects of recent conservation actions. For each of 30 declining species, attention
is focused on: (1) the external causes of population declines, (2) the demographic mechanisms
and (3) experimental tests of proposed external causal factors, together with the outcome of
(4) specific conservation measures and (5) agri-environment schemes. Although each species
has responded individually to particular aspects of agricultural change, certain groups of species
share common causal factors. For example, declines in the population levels of seed-eating birds
have been driven primarily by herbicide use and the switch from spring-sown to autumn-sown
cereals, both of which have massively reduced the food supplies of these birds. Their population
declines have been associated with reduced survival rates and, in some species, also with
reduced reproductive rates. In waders of damp grassland, population declines have been driven
mainly by land drainage and the associated intensification of grassland management. This has
led to reduced reproductive success, as a result of lowered food availability, together with
increased disturbance and trampling by farm stock, and in some localities increased nest predation.
The external causal factors of population decline are known (with varying degrees of certainty)
for all 30 species considered, and the demographic causal factors are known (again with varying
degrees of certainty) for 24 such species. In at least 19 species, proposed causal factors have been
tested and confirmed by experiment or by local conservation action, and 12 species have been
shown to benefit (in terms of locally increased breeding density) from options available in one
or more agri-environment schemes. Four aspects of agricultural change have been the main drivers
of bird population declines, each affecting a wide range of species, namely: (1) weed-control,
mainly through herbicide use; (2) the change from spring-sown to autumn-sown cereal varieties,
and the associated earlier ploughing of stubbles and earlier crop growth; (3) land drainage and
associated intensification of grassland management; and (4) increased stocking densities, mainly
of cattle in the lowlands and sheep in the uplands. These changes have reduced the amounts of
habitat and/or food available to many species. Other changes, such as the removal of hedgerows
and ‘rough patches’, have affected smaller numbers of species, as have changes in the timings
of cultivations and harvests. Although at least eight species have shown recent increases in their
national population levels, many others seem set to continue declining, or to remain at a much
reduced level, unless some relevant aspect of agricultural practice is changed.
Widespread population declines of farmland birds
are of major conservation concern in Britain and
other parts of Europe. Such declines have been rapid,
*Email: [email protected].
© 2004 British Ornithologists’ Union
massive and widespread, with some species experiencing more than 80% reductions in former numbers
and range in less than 20 years (Tucker & Heath 1994,
Fuller et al. 1995). Parallel declines have also occurred
in other components of farmland biodiversity,
580
I. Newton
including insects and wild plants (Wilson 1992,
Donald 1998, Sotherton & Self 2000, Preston et al.
2002). In this review, I shall assess the causal factors
underlying the population declines of particular bird
species in Britain, together with the effectiveness of
various conservation measures that have been
applied in recent years.
In most species affected, the main period of
population decline seems to have occurred between
1970 and 1990 (especially 1975–85), although in
some species (such as those affected by organochlorine pesticides) declines began earlier, and in others
they continued into or beyond the 1990s (Table 1;
see Fuller et al. 1995, Fuller 2000, Siriwardena et al.
1998, Chamberlain et al. 2001, Gregory et al. 2004
for Britain; Tucker & Heath 1994, Donald et al.
2001b for Europe as a whole). Substantial changes in
the farmland bird populations of Britain are by
no means new, however, as they have followed
every major change in agricultural practice that has
affected bird habitats and food supplies, at least over
the 250 years for which documentation is available
(Shrubb 2003). In the 19th century, the most marked
changes occurred as semi-natural habitats, such as
wetland, heath and moorland, were brought into
more intensive use, but in the 20th century, the most
marked changes occurred through the more intensive use of existing farmland. Compared with earlier
changes, recent population changes have affected
simultaneously a wider range of species, almost all of
which have declined, only small numbers having
apparently benefited, and increased in numbers or
range (see later).
Farmland birds have been defined either narrowly,
as those found primarily in farmed habitats, such as
Grey Partridge and Corn Bunting (see Appendix for
scientific names; only those of species not mentioned
in Table 1 are given in the text), or broadly to include
almost all landbirds that breed or winter in open
habitats. The latter reflects the fact that almost all
open land in Britain (70% of total land area) is used
for agricultural production. In this paper, I shall
adopt a broad view of farmland birds, as any species
that have been conspicuously affected by recent
changes in the methods of crop, meat or milk production. To exclude such species as Sparrowhawk
and Black Grouse, merely because they do not breed
in cultivated habitats, would be to ignore some of
the most dramatic examples of bird species being
affected by recent farming practice. Discussion is
confined to 30 breeding species whose populations
have declined markedly since 1950, and which have
© 2004 British Ornithologists’ Union, Ibis, 146, 579–600
been studied in detail. Other declining breeding
species are excluded, as are winter visitors.
SOURCES OF INFORMATION ON
BIRD POPULATIONS
Evidence for the role of agricultural change in the
declines of many bird populations has come partly
from temporal and spatial correlations between particular types of agricultural change and particular
bird declines (e.g. Chamberlain et al. 2000, Gates &
Donald 2000, Shrubb 2003), but also from detailed
field studies designed to find the crucial causal
factors (see species notes and references to Table 1
given in the Appendix). The main sources of information on the changes that have occurred in British
bird populations are the various wide-scale, longterm data-sets held by the British Trust for Ornithology (BTO). These include: (1) the Common Birds
Census, recently (and after a period of overlap)
replaced by the Breeding Bird Survey (BBS), both of
which were designed to measure year-to-year changes
in breeding bird abundance in various habitats, and
have therefore revealed the extent and precise timing of decline in most affected species; (2) two Atlas
projects, designed to map the breeding distribution
of all British bird species in 10-km squares throughout the country, at about 20-year intervals (1968–
72 and 1989–92) (Sharrock 1976, Gibbons et al.
1993); (3) the Ringing Scheme, providing recovery
data from which the annual mortality rates of various species have been calculated, and thus enabling
comparisons between periods of numerical stability,
increase and decrease; (4) the Nest Record Scheme,
from which the performance of individual breeding
attempts of various species has been calculated,
again enabling comparisons between periods of
stability, increase or decrease; (5) periodic surveys of
species of interest, not well covered by the other
schemes.
All these schemes have strengths and weaknesses
(Grice et al. 2004), but in our present context the
main problem lies with nest record data (Crick et al.
2003). In multi-brooded species, nest records give
no measure of the total seasonal production of young
per pair, which is the measure needed to understand
population changes. In some species, such as Corn
Bunting and Turtle Dove, nest record data indicated
an increase in individual nest success during a period
of population decline, while more detailed data
resulting from field studies indicated a shortening of
the breeding season, and hence in the total seasonal
Recent declines of farmland bird populations in Britain
581
Table 1. State of knowledge and outcome of conservation action in 30 bird species that have declined in Britain in association with recent
agricultural change. See Appendix for species notes and references.
Species
External
causal
factor1
Seed eaters
1 House Sparrow
2 Tree Sparrow
3 Linnet
4 Twite
5 Bullfinch
6 Yellowhammer
7 Cirl Bunting
8 Reed Bunting
9 Corn Bunting
10 Turtle Dove
F+N
F
F
H+F
H+F
F
F
H+F
F
H+F
Other passerines
11 Skylark
12 Meadow Pipit
13 Yellow Wagtail
14 Starling
15 Blackbird
16 Song Thrush
H+F
H(+F)
H+F
F
H+F
H+F
Waders and others
17 Lapwing
18 Snipe
19 Curlew
20 Redshank
21 Stone Curlew
22 Corncrake
Demographic
causal factor2
Surv.
Rep.
S*
S*
(R)
(R)
(R)
Experimental
test3
Local
conservation
action4
+
+
Agrienvironment
scheme5
National
policy
change6
+
+
S†
S*
S
S*
(R)
R
(R)
R
R*
R
+
+
+
+
+
+
+
+
+
R†
–
(–)
H+F
H+F
H+F(+P)
H+F
H+M
H+M
–
R*
R
R*
R
R
R
+
+
Gamebirds
23 Grey Partridge
24 Black Grouse
25 Red Grouse
H+F(+P)
H+F(+P)
H+F(+P+D)
S
Birds of prey
26 Sparrowhawk
27 Merlin
28 Peregrine
29 Kestrel
30 Barn Owl
Pesticide
Pesticide
Pesticide
H+F+N
H+F+N
S
S
S
+
+
+
+
+
+
+
+
+
+
+
R
R
+
+
+
+
+
+
R
R
R
(+)
(+)
(+)
+
+
+
+
+
+
S
S
S
D
D
S
I
S
D
D
D
D
D
D
I
I
+
S
S*
S*
Recent national
population
trend7
S
I
D
D
I
I
S
D
S
+
+
+
S
I
I
D
D
1
External causal factors: declines in habitat areas (H), food supply (F), nest-sites (N), or increases in predation or nest trampling (P),
parasitic disease (D) and losses to machinery (M).
2
Demographic causal factors: survival (S) or reproduction (R). *In a mathematical model, a change in S or R could account on its own
for the observed rate of decline. R values in parentheses indicate that change in nest success has been documented during the decline,
but total seasonal productivity has not been studied. –indicates no change. †Continental study only.
3
Scientifically designed experiment to test the effect of a proposed limiting factor, which is changed in one or more treatment areas, but
not in control areas, and the response of the population is compared between areas.
4
Management action taken in one or more areas (often nature reserves) which was followed by an increase in breeding density.
5
A scheme in which farmers are compensated for loss of production in return for carrying out some conservation-friendly activity including
set-aside.
6
National policy changes, usually promoted by legislation or subsidy schemes. Bird-friendly changes include the growing of oilseed rape,
which has probably benefited some seed-eating birds, notably Linnet and Reed Bunting (see text), and reduction in the use of
organochlorine pesticides, which benefited some predatory birds, and probably also some seed-eaters.
7
Based mainly on Breeding Bird Survey data, up until the year 2002: D, declining; I, increasing; S, stabilized at low level.
© 2004 British Ornithologists’ Union, Ibis, 146, 579– 600
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I. Newton
production of young (compare nest record data for
Corn Bunting and Turtle Dove from Siriwardena
et al. (2000) with seasonal data from Brickle &
Harper (2002) and Browne & Aebischer (2003)).
Because of this difficulty, other means have been
sought to provide reliable estimates of seasonal
productivity. For example, Newton (1999) used endof-breeding ratios of juveniles to adults in netted
samples to assess the annual productivity of Bullfinches over a 5-year period (see also Proffitt et al.
2004). Similar trapping data, as from the BTO Constant Effort or other netting schemes, might provide
reliable estimates of seasonal productivity in other
species (du Feu & McMeeking 1991; Peach et al. 1996),
providing that such measures are restricted to a brief
period at the end of the breeding season, and at dates
appropriate to the species concerned. The advantage
of such measures is that they incorporate the effects,
not only of brood numbers, but also of immediate
post-fledging survival, which is another (usually
unknown) component of reproductive success. Clearly,
we need good measures of seasonal production, if we
are fully to understand the demographic parameters
that have underlain population declines.
In addition to the BTO data, other wide-scale or
long-term information on some bird species is held
by other organizations, such as the Game Conservancy Trust, the Centre for Ecology and Hydrology
and the Royal Society for the Protection of Birds.
Additional (usually shorter-term) information is
held by the many individuals or university groups
who have conducted detailed studies of individual
species in particular localities. In recent years, most
such field studies have been aimed mainly at addressing conservation problems (see later examples).
COMPONENTS OF AGRICULTURAL
INTENSIFICATION
The main problem in finding causes of bird population declines is that agricultural intensification is not
a single process, but has several components, each of
which can affect different species. Moreover, these
various aspects of change have occurred more or less
simultaneously and interdependently, which makes
the role of any one change hard to separate from the
confounding effects of others. Thirdly, the problems
have mostly been studied retrospectively, only after
the agricultural changes and bird population declines
had been underway for several years.
The main components of recent agricultural
change in Britain can be listed as follows, while data
© 2004 British Ornithologists’ Union, Ibis, 146, 579–600
on the extent or spatial scale of each type of change
can be found in Chamberlain et al. (2000), Fuller
(2000) and Shrubb (2003):
1 Massive increases in the use of agro-chemicals,
both pesticides and fertilizers. Rising pesticide use is
reflected in increases in the range of chemicals used,
the acreage treated and the numbers of applications
per year. Some such chemicals, notably the organochlorine insecticides, have had direct effects on birds,
causing reproductive failures or enhanced mortality
(Newton 1979, 1986, 1998, Ratcliffe 1993), while
others have affected birds indirectly through reducing their food supplies (Potts 1986, Newton 1995,
1998). Herbicide use reduces weed growth and seed
production, which leads not only to loss of immediate food supply, but to long-term depletion of the
seed bank in the soil. Progressive increases in the
numbers of herbicides, modes of action and formulations available have gradually expanded the range
of weed species that can be controlled effectively in
each crop type. Weeds also support insects, which
form important foods for some bird species (Potts
1986). Direct pesticide effects were evident in some
birds of prey and (mainly in the years around 1960)
some seed-eaters; indirect effects are evident in a
wide range of seed- and insect-eaters.
2 Removal of hedges and other uncultivated areas to
produce larger fields and more land for crop production. This activity has greatly reduced the amount of
semi-natural habitat that existed within the agricultural matrix. Some bird species both nest and feed
within such habitat, while others nest there but feed
in neighbouring fields. In addition, mechanization
has brought a change in hedgerow management, many
former tall and thick hedgerows being converted to
short, narrow ones, with effects on bird populations
(for relationships between hedgerow structure, verge
features, landscape context and bird populations, see
Arnold 1983, Osborne 1984, Green et al. 1994, Parish
et al. 1994, Macdonald & Johnson 1995, Gillings &
Fuller 1998, Hinsley & Bellamy 2000). Such changes
are likely to have affected most hedgerow-nesting
species, and others using semi-natural habitats.
3 Change from spring ploughing to late summer
ploughing of cereal stubbles soon after harvest. This
change has removed the supply of spilled grain and
other seeds on the ground, on which many seed-eaters
formerly fed in winter, as well as the spring-sown
grain itself, which was an important dietary component of several species at a time of year when other
foods were scarce. It is likely to have affected all seedeating species that fed in winter stubbles (for further
Recent declines of farmland bird populations in Britain
discussion, see Potts 2003, Evans et al. 2004). This
procedural change also removed the invertebrate
food supply and weed seeds provided by fresh till
in spring and the short-vegetation (including undersown stubble) nesting and feeding habitat favoured
by Lapwings, Skylarks and others (autumn-sown
cereals having grown too tall and dense by spring).
Spring-sown cereal crops were also managed with
less chemical input.
4 Extensive land drainage, which, through lowering
the water-table, changed wet grassland to dry grassland or enabled a change to cereal culture. This has
affected many dampland species, notably certain
waders, but probably also other species, such as European Starling, which feed on invertebrates from near
the soil surface.
5 The trend from mixed farms, producing a variety
of plant and animal products, to monoculture arable
(mainly in the east) or monoculture grassland (mainly
in the west). This change has reduced the diversity of
habitats available on individual farms, affecting species such as Lapwing, which depended on a localized
mixture of habitats, or Skylark, which benefited from
being able to move from one crop-type to another
during the course of a single breeding season. It also
led to a reduction in the area of root crops (important
because of weed growth, Hancock & Wilson 2003),
oats and other minority crops (providing seed-rich
winter stubble), and the almost total elimination of
bare fallow (an important habitat for several nesting
species). Probably many species were affected by this
change, including sparrows, finches, buntings and
Skylarks (Robinson 2001).
6 The trend to earlier harvesting dates, caused by a
combination of earlier sowing dates, earlier ripening
cereal varieties and a change from hay to silage (grass
harvested green at an earlier growth stage, allowing
repeated cuts through the season). This means that
more cultivation procedures (including harvest)
fall within bird breeding seasons, causing greater
destruction of eggs and chicks of field-nesting species,
such as Yellow Wagtail and Corn Bunting (e.g. Crick
et al. 1994, Court et al. 2001, Henderson et al. 2004).
In at least the Corncrake and Stone Curlew, destruction of eggs and chicks can be sufficient to cause population declines (Norris 1947, Aebischer et al. 2000).
7 More intensive grassland management, involving
use of inorganic fertilizer and more frequent reseeding (Vickery et al. 2001). The fertilizer stimulates
grass growth, making it no longer suitable for some
ground-nesting bird species, and eliminating through
competition many broad-leaved plant species. Loss
583
of plant diversity in turn reduces insect diversity and
abundance. Re-seeding reduces invertebrate densities
in the soil (which increase with age of grassland,
Tucker 1992). The increase in grass growth can support increased densities of cattle or sheep, or more
frequent cutting for silage, both of which result in
greater destruction of eggs and chicks. This change is
likely to have affected all grassland species. Moreover, the sward assumes a more uniform and denser
structure, and generally lacks the tussocks favoured
by many species of ground-nesting birds, or the bare
patches in which they can feed.
8 In upland areas, a massive increase in sheep-stocking
densities, which changes habitat structure, sward
height and composition, and reduces plant flowering
and seeding, together with the densities of insects,
many of which are eaten by birds. Probably almost all
species of open upland habitats are affected.
Over the years, increasing mechanization and technology have underpinned some of these changes, and
at one time or another most have been encouraged
by commodity price support and by payment of
grants or subsidies, which made previously uneconomic practices profitable (for historical development of agricultural policy see Shrubb 2003). While
some changes occurred more or less simultaneously
over the whole country, others occurred earlier in
the drier east than in the wetter west. The general
trends were towards loss of grass to give more arable
in the east, and loss of arable to give more ‘improved’
grass in the west, producing generally less diverse
landscapes in both regions.
PROCESSES LEADING TO
POPULATION DECLINES
In studying population declines, it is important to
distinguish between the external (environmental)
factors that cause a decline and the intrinsic demographic factors (such as reduced survival or reproductive rate) that underlie the decline (Newton 1991,
1998, Green 1995). Thus, within suitable habitat, a
population might be said to decline because of
food shortage (the ultimate cause) or because of the
resulting mortality (the proximate mechanism). In
attempts to manage bird populations, it is the external limiting factors that must be changed before any
lasting change in population level can be achieved;
the necessary demographic changes will follow naturally. However, knowledge of the demographic
changes can often help to pinpoint the external
causal factors, or at least to distinguish whether
© 2004 British Ornithologists’ Union, Ibis, 146, 579– 600
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I. Newton
population decline is associated with reduced breeding production or reduced survival.
The series of events that lead to some population
declines are short and simple. For example, the
killing of chicks during grass-cutting can reduce the
reproductive rate of Corncrakes to such an extent
that it causes rapid population decline (Norris 1947,
Green et al. 1997). This is a single-step process, which
can be easily identified. Likewise, the destruction of
clutches during the rolling and harrowing of arable
fields in spring can lead to population decline in
Stone Curlews (Green & Griffiths 1994). Population
declines of other species are due to longer, multi-step
sequences of events, which are much harder to work
out. Some well-researched examples are given in
Figures 1–4, and the Appendix.
5 Has the species concerned been shown to benefit by
increased breeding density from any agri-environment
scheme, including set-aside (leaving arable land fallow),
or any other national policy change (but note that
some existing schemes may not have operated for long
enough to have yet promoted measurable changes in
bird breeding densities)?
6 Has a previous substantial decline in population been
reversed, giving a sustained and statistically significant
increase over five or more recent years (up to 2002)?
My attempts to answer these questions, mostly from
published research findings, are summarized in Table 1,
which also gives footnotes on each species with supporting references. Although species have been studied individually, they fall readily into distinct groups,
according to the dominant agricultural drivers.
CURRENT KNOWLEDGE OF
POPULATION DECLINES AND
EFFECTIVENESS OF
CONSERVATION MEASURES
Seed-eaters
In this section, I discuss the state of current knowledge
and conservation action for 30 species of birds that are
thought to have declined in Britain because of some
aspect of agricultural change. They do not include all
such declining species, but those discussed have been
well enough studied to examine in detail. Some of these
30 species, such as Corn Bunting and Grey Partridge,
are obvious farmland specialists, while others, such as
Merlin and Black Grouse, are not normally regarded
as farmland species, but have nevertheless been greatly
affected by changes in agricultural practice. For each
of these species, six main questions are addressed:
1 What have been the agricultural drivers of population decline, e.g. drainage, herbicide use, increased
stocking densities?
2 Have the above agricultural changes brought
about reductions in habitat area, food or nest-sites,
or increases in predation, parasitism/disease, humaninduced mortality or competition, all of which fall
under the heading of ‘external limiting factors’?
3 What are the demographic changes that have brought
about population decline: reduced survival, reduced
reproduction or both? As we are dealing with national
populations, the effects of any change in movement
patterns (immigration/emigration) can be ignored.
4 Has the proposed limiting factor (habitat, food or
whatever) been tested by experiment or by local conservation action (as in nature reserve management or
nest-site provision), resulting in increased breeding
density?
© 2004 British Ornithologists’ Union, Ibis, 146, 579–600
In all ten species considered, the main causal factor
identified was decline in food supply (Table 1, Fig. 1),
but some species have also suffered considerable
reduction in habitat (Bullfinch and Turtle Dove
through loss of tall hedgerows, Twite through loss
of saltmarsh wintering habitat, and Reed Bunting
through drainage of wet areas), and the House
Sparrow perhaps also from reduction in nest-sites.
Declines in food supply were caused mainly by:
(1) herbicide use, which reduces current-year weedseed production, and leads to long-term depletion
of the seed bank in the soil; and (2) loss of winter
stubble fields, with their associated weed-seeds and
spilled grain, resulting from the switch from springsown to autumn-sown cereals. The relative importance of these seed sources varies between species,
depending on their dietary needs, and the House
Sparrow has probably also suffered from the increased
bird-proofing of stores for grain and other animal
feed. Herbicide use also reduced the abundance of
weed-dependent insects that some seed-eaters feed
to their young.
At least six seed-eating species have experienced a
decline in survival rate during the period of decline;
and in at least four of these, the measured decline
in survival was found in a modelling exercise to be
capable of accounting for the observed rate of
population decline, without any concurrent change
in reproductive rate. At least three species have
experienced decline in seasonal reproductive rate,
and in one (Turtle Dove) this was deemed sufficient
on its own to account for the observed rate of decline.
Changes in the success of individual nesting attempts
Recent declines of farmland bird populations in Britain
585
Figure 1. Proposed sequence of events through which herbicide use causes population declines in seed-eating birds, some species of
which also require insects for their chicks. The relative contributions of seed reduction (route A) and insect reduction (route B) seem to
have varied between species, as shown. For references, see Appendix.
were recorded in seven species (in five increases, in
two decreases), but as explained above, in multibrooded species these measures do not necessarily
translate into changes in seasonal production. They
are therefore of limited value in our present context.
At least five seed-eating species showed increased
breeding densities after the local introduction of
agri-environment schemes. The spread of oilseed
rape (from less than 1% of arable land in the 1950s
to more than 8% in 2000) has almost certainly
provided additional food for several species (notably
Linnet) and also additional nesting habitat for Reed
Buntings. In some seed-eating species, local increases
resulting from management action have been insufficient to reverse overall downward national trends,
although numbers of five species seem to have stabilized in the last few years (Table 1). The only seedeater that has shown substantial increase in response
to management is the Cirl Bunting, which is effectively
confined to parts of one county. Its numbers increased
about four-fold over 10 years in response to increased
food supplies provided by a targeted agri-environment
scheme.
Other passerines
The Skylark is one of the most studied species. Its
decline is attributed to loss of habitat: the replacement of rough grassland by managed grassland, and
of spring-sown by autumn-sown crops (which soon
grow too tall for nesting Skylarks), and also to reduction in food availability (mainly insects in summer,
small weed-seeds in winter). There are insufficient
ring recoveries to check for possible changes in
mortality rates, but the breeding season is curtailed
in arable farmland because of rapid crop growth,
through which the habitat becomes unsuitable.
Although some Skylarks switch from one crop to
another during the course of the breeding season, not
all pairs now have access to such alternative habitat,
leading to a net reduction in offspring production.
Skylarks have responded by increased breeding
density and seasonal success to the provision of
unsown patches in cereal fields, to unsprayed setaside fields and to local agri-environment schemes,
but such local effects have not so far reversed the
national population decline.
© 2004 British Ornithologists’ Union, Ibis, 146, 579– 600
586
I. Newton
The Meadow Pipit has suffered from loss of
habitat (notably rough grassland), and probably also
from decline in insect food supplies consequent
upon overgrazing (see studies of Black Grouse), but
is the least known of all the species listed in Table 1,
and is in obvious need of further study. The Yellow
Wagtail nests both in wet grassland and in dry,
sparsely vegetated arable land. It has suffered from
large reductions in nesting habitat, resulting from
the drainage and more intensive management of
grassland, and from the change from spring-sown
to autumn-sown arable crops, which grow too tall
and thick by spring. It has responded by increased
density to raised water levels (and winter flooding)
of some grassland nature reserves. The Starling has
experienced a massive reduction in food supply, caused
mainly by land drainage and more intensive grassland
management, which has reduced the availability of
invertebrates in the surface soil, and by reductions in
the number of accessible feed-sites for farm stock. In
some eastern areas, the conversion of former grassland
to arable has also reduced the acreage of potential
foraging habitat. Long-term population decline has been
associated with reduced survival, and (in a Finnish
study) with reduced breeding success. The Blackbird
and Song Thrush have suffered from loss of habitat
(especially hedgerows and field margins), and may
also have experienced reductions in food supplies
resulting partly from greater field drainage, which
makes soil invertebrates less accessible. Both have
experienced reduced survival, deemed sufficient in a
modelling exercise to account for the observed rate
of decline in the 1970s and 1980s, but both have shown
some population recovery since 1994. Various management changes and predator control at the Allerton
Research and Education Trust farm in Leicestershire
were followed by substantial increases in the breeding density and seasonal productivity of both species,
but as all changes were brought in simultaneously, it
is as yet uncertain which were most important.
Waders, Corncrake and gamebirds
Four species have suffered mainly from the drainage
of damp grassland. It is difficult to decide whether to
put their declines down to loss of habitat or to loss
of food, because as the ground dries, soil invertebrates become less accessible (Fig. 2). Drainage is
usually followed by ploughing, re-seeding and
fertilizer application, which in turn leads to more
uniform sward structure, more rapid grass growth,
decline in non-grass plant species (and associated
© 2004 British Ornithologists’ Union, Ibis, 146, 579–600
Figure 2. Proposed sequence of events through which the
draining and re-seeding of wet grassland causes population
declines in waders. Re-seeding and fertilizing improves grass
growth, which allows greater stocking densities or multiple grass
cuts for silage. Both these effects can result in greater nest
destruction. For references, see Appendix.
insect populations), earlier and more frequent
mowing, or increased stocking densities with sheep
or cattle. Increased livestock numbers lead to greater
disturbance of nesting birds (which may in turn lead
to increased egg and chick predation), and increased
trampling of nest contents. Nest failure rates have
been quantified in relation to stocking densities of
cattle and sheep from studies in The Netherlands
(Beintema & Muskens 1987, Beintema et al. 1997).
In addition to the effects of land drainage, Lapwings
have largely disappeared from former mixed farming
areas, which no longer offer the combination of
spring-sown arable and unimproved grass fields in
close proximity. In all four species, decline in population was associated with reduced reproductive success, and in two of them, reduced reproduction was
deemed sufficient on its own to account for observed
rates of decline.
At least three of the four dampland wader species
listed in Table 1 have increased in numbers and nest
success following the raising of ground-water levels
on grassland nature reserves, and the Lapwing has
responded in a similar way to at least one agrienvironment scheme. However, the overall national
populations of at least three species are still in
decline, the Snipe having increased slightly in BBS
Recent declines of farmland bird populations in Britain
587
Figure 3. Proposed sequence of events through which the overgrazing of open upland vegetation causes population declines in grouse
and other species. The relative contributions of food-plant reduction (route A) and insect reduction (route B) seem to have varied
between species. For references, see Appendix.
counts in the last 8 years (as opposed to declining in
surveys of wet meadow birds).
In the Stone Curlew, population decline has been
attributed partly to loss from many areas of sparsely
vegetated spring arable land, and short-sward seminatural dry grassland, and partly to destruction of
eggs and chicks on remaining suitable arable areas by
farm machinery. Similarly, in the Corncrake, decline
is attributed partly to loss of damp meadows, and
partly to the destruction in remaining meadows of
eggs and chicks during mechanized grass cutting. In
earlier centuries, the losses were smaller because
grass was cut by hand and later in the year, as it was
used to make hay rather than silage. In both species,
local conservation action, within the framework of
appropriate agri-environment schemes, has greatly
reduced nest losses, resulting in increased national
population levels.
The three gamebirds listed in Table 1 have all suffered from loss of habitat and food supplies. When
populations decline, landowners tend no longer to
employ gamekeepers, and predation rates rise, further
contributing to population declines. In the Grey
Partridge, decline seems to result in the first instance
mainly from reduction in the abundance of insects
eaten by chicks, but reduction in field margins results
in a scarcity of nesting habitat (and the more weedrich and insect-rich cropland at the edges of fields,
Green 1984), while lack of predator control results
in greater predation both on nest contents and on
adults, the incubating females being especially vulnerable. The series of events leading to population
decline (Fig. 1) has been confirmed by experiment,
and Grey Partridge populations have increased in
response to local conservation measures (including
the non-spraying of field edges) and agri-environment
schemes, and the overall national population seems
to have stabilized at a low level.
In Black Grouse, which are now mainly confined
to moorland and other rough grazing land in the
uplands, numerical declines have been attributed
primarily to increased stocking densities, which reduce
the sward height and the diversity of plant populations (Fig. 3). Insects suitable for chicks decline in
abundance, leading to greatly reduced chick survival,
and hence to population decline. Populations in several experimental areas have responded to reduced
livestock densities (and greater insect abundance),
© 2004 British Ornithologists’ Union, Ibis, 146, 579– 600
588
I. Newton
Figure 4. Proposed sequence of events through which the use of organochlorine pesticides causes population declines in some
predatory birds. DDE is the main metabolite of the insecticide DDT, and acts primarily by causing eggshell thinning and reduced breeding
success. HEOD is the main metabolite of aldrin and dieldrin, is much more toxic than DDE and acts by increasing mortality rates. The
relative importance of DDE and HEOD in causing population declines seems to have varied between regions, depending on usage
patterns. For references, see Appendix, and Newton (1998).
and in some (but not all) areas also to predator control. The Red Grouse has declined mainly because of
reduction in the area of heather moorland. In some
areas this is caused by afforestation, but in others by
increased sheep densities, through which heather is
gradually converted to grassland. Other factors in the
decline of Red Grouse populations include reduced
predator control, and increased incidence of the viral
disease louping ill (see below). To my knowledge, no
recent attempts to increase Red Grouse numbers
(other than by predator control) have been published, and the national population shows no sign of
increasing.
Birds of prey
Three raptor species suffered massive population
declines in the late 1950s and 1960s through the
direct effects of organochlorines on breeding success
and survival (Fig. 4). These chemicals are persistent,
and highly fat-soluble, so they accumulated in the
tissues of prey species, from which they concentrated
to even higher levels in some raptor species. The
© 2004 British Ornithologists’ Union, Ibis, 146, 579–600
chemical DDE (the main metabolite of the insecticide DDT) caused eggshell thinning, which led to
egg breakage and reduced breeding success, while
the more toxic cyclodiene compounds (aldrin and
dieldrin) killed birds outright. These various effects
were tested on captive birds of related species. As a
result of these and other findings, the use of organochlorines was progressively reduced over a period
of years, and almost ceased from 1986 onwards.
Accordingly, the three species that had been most
affected in Britain (Sparrowhawk, Peregrine and
Merlin) steadily recovered through the 1970s and
1980s, and in 20 years they had recolonized regions
from which they had been extirpated. This is a major
conservation success story, and the main threat to
these birds may now stem from declines in their various prey species or from illegal persecution.
Two other birds of prey, the Kestrel and Barn Owl,
also suffered from organochlorine use, but showed
only regional population declines, from which they
rapidly recovered in the 1970s (Newton et al. 1991,
1999). Since then, they have declined more generally, owing mainly to the loss and overgrazing of
Recent declines of farmland bird populations in Britain
rough grassland that supports their principal prey
species, the Field Vole Microtus agrestris. In addition,
both have suffered, at least in some areas, from
reductions in the availability of nest-sites, mainly
tree cavities, but (in the Barn Owl) also disused
cottages and farm buildings. Both species have
responded by increased breeding density and success
to improvements in food supply (brought about by
fencing out sheep from rough grassland) and by provision of artificial nest-sites in areas where natural
sites were scarce. Unless the trends in grassland management and nest-sites can be reversed, these two
species seem destined to decline further.
SUMMARY OF FINDINGS
Of the various changes on farmland in recent decades, four emerge as the major drivers of declines in
bird populations: (1) pesticide use (especially herbicides); (2) late summer ploughing of cereal stubbles,
followed by rapid re-sowing and early crop growth;
(3) drainage and intensification of lowland grassland
management; and (4) increased stocking densities
(mainly cattle in the lowlands and sheep in the uplands).
Each of these changes has had serious effects on a
wide range of species. Other changes, such as the
removal of hedgerows and earlier harvesting of grass
and cereals, have affected a smaller range of species.
Most of these changes have resulted in reductions
in bird habitats and/or food supplies, which have
emerged as the main limiting factors underlying population declines in 27 of the 30 species considered
(the only exceptions being the three raptor species
whose populations collapsed following the introduction of organochlorine insecticides) (Table 2). Other
evidence for the importance of food supplies has
emerged from other types of study, for example
where breeding or wintering densities, survival or
breeding success are greatest in localities with greater
food supplies (for winter densities of seed-eating
birds see Donald & Evans 1994, Wilson et al. 1996,
Robinson & Sutherland 1999, Moorcroft et al. 2002,
Hancock & Wilson 2003; for breeding success of
Corn Buntings see Brickle et al. 2000); on organic
compared with conventional farms (Christensen et al.
1996, Wilson et al. 1997, Chamberlain et al. 1999b,
Chamberlain & Wilson 2000); on first-year set-aside
compared with cropped fields (Watson & Rae 1997,
Henderson et al. 2000); in localities with pesticide
use compared with localities with no pesticide use
(Boatman et al. 2004); or in seed-bearing ‘game crops’
compared with conventional crops (Stoate et al.
589
Table 2. Summary of existing knowledge and conservation
action for 29 species in Britain whose populations have declined
during the past 50 years in association with agricultural
changes. From data in Table 1.
Agricultural driver known
External causal factor known1
Demographic causal factor known2
Experimental test positive3
Local conservation action, positive response4
Agri-environment scheme positive response5
Other policy change, positive response6
National population increase7
30
30
24
15
19
10
12
3 (+2)
8 (27%)
}
1
Habitat reduction 20 species, food reduction 25 species,
nest-site reduction three species, pesticide poisoning three
species, agricultural operations two species, predation four species,
parasites / pathogens one species, competition no species (see
text).
2
Species: 1, 2, 4, 6 –11, 14 – 28.
3
Species: 1, 2, 7, 11, 15 –17, 22 – 24, 26 – 30.
4
Species: 13, 17, 18, 20 – 24, 29 – 30.
5
Species: 1, 6 – 9, 11, 14, 17, 21– 24.
6
Species: 3, 8, 26 – 28.
7
Species: 7, 15, 16, 18 (see text), 21, 22, 27, 28.
Species numbered as in Table 1.
2003). Yet other studies have linked the temporal
change in regional or local agricultural practice with
the timing of declines in invertebrate and bird densities (Benton et al. 2002).
Predation has not emerged as the main causal
factor for any of the species considered, only as a secondary or associated factor, chiefly in ground-nesting
birds. All the species listed, as with most other bird
species in Britain, suffer from predation, and in some
species predation rates have been recorded as higher
than in the past. Several species of predators, notably
Red Fox Vulpes vulpes, Carrion Crow Corvus corone
and Magpie Pica pica, have increased in numbers
during recent decades. Their increases have been
attributed to reductions in the numbers of gamekeepers, and to increases in food supplies, contingent
upon changes in land-use. In upland areas, increased
sheep densities have led to ecological overgrazing in
many areas, and to increased sheep mortality, which
has provided more carrion. In lowland areas, the
decline in Grey Partridge numbers has encouraged
many landowners to rear and release large numbers
of Pheasants Phasianus colchicus and Red-legged
Partridges Alectoris rufa, an activity which also provides more food to sustain predator populations. The
greater areas of short-sward grassland may also have
favoured corvid populations, as it provides additional foraging habitat for these birds.
© 2004 British Ornithologists’ Union, Ibis, 146, 579– 600
590
I. Newton
Some land-use changes may predispose prey
species to extra predation (Evans 2004): examples
include the draining and re-seeding of grassland,
which supposedly makes ground nests more visible
or accessible to predators; hedge removal, which for
some species concentrates nests in smaller areas of
remaining habitat that are easier for predators to
search; and reductions in food-supplies, which make
hungry passerine broods call more, and attract the
attention of predators (e.g. Evans et al. 1997, Brickle
et al. 2000). Nest success of some species in different
areas has been correlated with densities of predators
(notably corvids, Stoate & Szczur 2001), and predator
removal studies have led to increased nest success
and breeding density in a number of species, including Red Grouse, Golden Plover Pluvialis apricaria
and Lapwing on heather moors (Tharme et al. 2001),
and Grey Partridge, Song Thrush, Blackbird and
other passerines on farmland (Tapper et al. 1996,
Stoate & Szczur 2001, Donald et al. 2002). On the
other hand, no relationships emerged between local
trends in songbird numbers and local trends in Magpie
or Sparrowhawk numbers, two predators sometimes
suspected of causing declines in songbird populations (Gooch et al. 1991, Dix et al. 1998, Thomson
et al. 1998).
Disease is hard to detect in wild bird populations,
but ‘louping ill’ has emerged as a factor leading to
decline in Red Grouse densities in some areas.
This viral disease often kills grouse, but persists in
alternative hosts, which include sheep. Its incidence
in grouse has increased greatly on some moors on
which sheep densities are high, leading to marked
declines in grouse densities. Because of its dependence on high sheep densities, frequent louping ill can
be regarded as another legacy of recent agricultural
policy.
Most species of birds overlap in their dietary and
other needs with other bird species and with other
animals. Resources used by one species are not
then available to another. It is reasonable to suppose
therefore that the densities of many species are
lower than they might otherwise be, because of competition for shared resources, but the effects of competition are not necessarily greater now than in the
past. So far as I am aware, increased competition
has not been suggested as a factor in farmland bird
declines. However, it is perhaps one additional factor
worth examining in the House Sparrow. In former
times, when House Sparrows were at their peak
abundance, they were the only birds that lived in
towns in such close association with people. They
© 2004 British Ornithologists’ Union, Ibis, 146, 579–600
had access to everything edible that people provided. Their recent decline in urban areas has
occurred over a period when increasing numbers of
other seed-eaters (including Collared Doves Streptopelia decaocto) have been attracted into gardens by
special food provision. It would be surprising if these
other species did not also remove some food items
that would formerly have been available to House
Sparrows. In addition, the effect on other birds of
releasing 20–30 million Pheasants into the countryside each year has never been assessed. Pheasants are
normally fed with grain for most of the year (late
summer to spring), which could benefit other birds,
but they also find some of their own food, which
could adversely affect other species.
Agricultural operations, leading to destruction of
eggs or chicks, have been identified as a major causal
factor in the population declines of two species
(Stone Curlew and Corncrake), but also contribute
to nest failures in other ground-nesting species,
especially during the harvest of silage (for Skylark
see Poulsen et al. 1998) or early ripening cereals (for
Corn Bunting see Crick et al. 1994, Brickle & Harper
2002; for Montagu’s Harrier Circus pygargus in
Europe see Arroyo et al. 2002).
Apart from the raptors affected by organochlorine
pesticides, only three species that had declined
have shown substantial increases in at least the last
5 years, namely Cirl Bunting, Corncrake and Stone
Curlew. These three all have restricted distributions
within Britain, and relatively small populations confined to farmland, which can be managed intensively
within the framework of agri-environment schemes.
Without continued year-by-year management, these
species would all decline, and probably become
confined to nature reserves or disappear from Britain
completely within a few years. For three other species, BBS indicates smaller, but significant, increases
over the past five or more years, namely Blackbird,
Song Thrush and Snipe, although the evidence for
the Snipe is equivocal (see Appendix).
Although it is too early to assess properly the effects
of recently introduced agri-environment schemes,
earlier schemes were most successful when targeted
to the needs of particular species, such as Cirl
Bunting, Lapwing, Stone Curlew and Corncrake, and
of some seed-eaters through winter seed provision
(Aebischer et al. 2000, Bradbury & Allen 2003). More
recent schemes have led to localized increases in the
breeding and wintering densities of several other
species (Bradbury et al. 2004), but without detailed
study, it is as yet uncertain whether these local
Recent declines of farmland bird populations in Britain
increases were due to immigration, rather than to
the improved survival and breeding success of local
birds. Only a general improvement in survival or offspring production could lead to recovery of national
populations. While reversing the declines in farmland birds requires substantial changes to existing
farming systems, such changes do not necessarily
require a reversion to previous systems, providing
that appropriate management practices can be incorporated in other ways.
Considering the massive changes that have occurred
on farmland in recent decades, during the drive for
intensive crop production, it is perhaps surprising
that not all species have declined. However, the few
species involved have benefited in other ways, and
a plausible reason for their lack of decline is usually
apparent. For example, Woodpigeons Columba
palumbus were once largely dependent in winter on
the clover sown into cereal stubbles. As this crop
disappeared in the 1960s, Woodpigeons began to
decline, but soon increased again when a substitute
winter food-supply, namely the young leaves of oilseed
rape, became widely available (Inglis et al. 1990).
Stock Doves Columba oenas have also increased
greatly since the 1960s. Their numbers had previously been greatly reduced by organochlorine
pesticides (O’Connor & Mead 1984), so at least part
of their increase represents population recovery following reductions in organochlorine use, but latterly
they may also have benefited from the spread of
oilseed rape, the leaves of which form an important
winter food. It is perhaps more surprising that
three species of finches have not declined, namely
Chaffinch Fringilla coelebs, Greenfinch Carduelis
chloris and Goldfinch Carduelis carduelis. However,
Chaffinches are major beneficiaries of Pheasant feed
sites, which are maintained throughout the winter,
and Chaffinches and Greenfinches have fed increasingly in gardens since the 1960s, following the provision of peanuts and other suitable seeds. The same
is true for Goldfinches since the early 1990s, but in
any case a large proportion of Goldfinches that breed
in Britain winter further south, mainly in Spain
where some favoured food-plants grow and seed
throughout the winter (Newton 1972). However,
further work is needed to determine whether these
plausible guesses can be turned into well-founded fact.
In conclusion, gaps still exist in our understanding
of the causal factors behind the declines in some
species affected by agricultural change, as indicated
in Table 1. In lesser-known species not discussed in
detail here, such as Ring Ouzel Turdus torquata and
591
Whinchat Saxicola rubetra, population declines may
well be due to one or more of the same causal factors, in which case these species could also benefit
from remedial measures designed for better-studied
species. Despite the gaps in our knowledge, the main
drivers of bird population declines are now clear, and
it is these drivers that must be addressed if recoveries
are to occur. One obvious way to reverse population
declines would be to revert to traditional systems of
land use, but such changes seem unlikely to happen,
except on the small scale possible on nature reserves
and other special sites. Alternatives include encouraging farmers to adopt different procedures, or finding different ways, within the context of modern
agriculture, of providing the food or other resources
that birds and other wildlife require. Both of these
options require a shift in the subsidy system, so that
farmers do not suffer financially from adopting more
benign practices. Recent reforms to the Common
Agricultural Policy, notably the de-coupling of subsidies from crop and meat production, may provide
opportunities for more widespread conservation
management. The main immediate requirements,
however, are for continued monitoring of bird
populations, at local as well as national levels, in
order to assess the effectiveness of existing and new
agri-environment schemes. Only by careful appraisal
of the application and consequences of these schemes
can their prescriptions be modified in future to
achieve greater environmental benefits.
I am grateful to James Goodhart, Rhys Green and Jeremy
Wilson for helpful comments on the manuscript, and
also to Phil Grice and Juliet Vickery in their capacity as
referees.
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heather-dominated moorland. J. Appl. Ecol. 38: 439 – 457.
Thomson, D.L., Baillie, S.R. & Peach, W.J. 1997. The demography
and age-specific survival of song thrushes during periods of
population stability and decline. J. Anim. Ecol. 66: 414 – 424.
Thomson, D.L., Green, R.E., Gregory, R.D. & Baillie, S.R.
1998. The widespread declines of songbirds in rural Britain
do not correlate with the spread of their avian predators.
Proc. R. Soc. Lond. B 265: 2057– 2062.
Tiainen, J., Hanski, I.K., Pakkala, T., Piiruoinen, J. & Yrjölä, R.
1989. Clutch-size, nestling growth and nestling mortality of the
Starling Sturnus vulgaris in south Finnish agro-environments.
Ornis Fenn. 66: 41– 48.
Toms, M.P., Crick, H.Q.P. & Shawyer, C.R. 2001. The status of
breeding Barn Owls in the United Kingdom 1995 –97. Bird
Study 48: 23–37.
Tucker, G.M. 1992. Effects of agricultural practice on field use by
invertebrate-feeding birds in winter. J. Appl. Ecol. 29: 779 –
790.
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Tucker, G. & Heath, M. 1994. Birds in Europe: Their Conservation Status. Cambridge: Birdlife International.
Vanhinsberg, D.P. & Chamberlain, D.E. 2001. Habitat associations of breeding Meadow Pipits Anthus pratensis in the
British uplands. Bird Study 48: 159 –172.
Vickery, J.A., Tallowin, J.R., Feber, R.E., Asteraki, E.J.,
Atkinson, P.W., Fuller, R.J. & Brown, V.K. 2001. The management of lowland neutral grasslands in Britain: effects of
agricultural practices on birds and their food resources.
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Village, A. 1990. The Kestrel. Calton: T. & A.D. Poyser.
Wakeham-Dawson, A., Szoszkiewicz, K., Stern, K. &
Aebischer, N.J. 1998. Breeding skylarks Alauda arvensis on
Environmentally Sensitive Area arable reversion grass in
southern England: survey-based and experimental determination of density. J. Appl. Ecol. 35: 635 – 648.
Warren, P. & Baines, D. 2004. Black Grouse in northern
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Watson, A. & Rae, R. 1997. Some effects of set-aside on breeding birds in northeast Scotland. Bird Study 44: 245 – 251.
Whitehead, S.C., Wright, J. & Cotton, P.A. 1995. Winter field
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preferences and the availability of prey. J. Avian Biol. 26:
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Wilson, J.D., Evans, A.D., Browne, S.J. & King, J.R. 1997.
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England. J. Appl. Ecol. 34: 1462–1478.
Wilson, J.D., Taylor, I. & Muirhead, L.B. 1996. Field use by
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Received 27 April 2004; revision accepted 4 August 2004.
APPENDIX
Species notes and references to Table 1
House Sparrow Passer domesticus – Declined in urban
as well as in rural areas; several causal factors mooted,
including decline of food supply (insects and seeds),
increased predation from an expanding cat population, increased pollution from traffic in cities, and in
some areas reduced availability of nest-sites (stemming from building repairs and conversions), but
further work needed. In one experiment, responded
to provision of extra food on some farms where
numbers previously declined, but not on others where
numbers were previously stable or increasing (Hole
et al. 2002). Decreased survival during the years of
Recent declines of farmland bird populations in Britain
decline (Siriwardena et al. 1999); also increased nest
success (Siriwardena et al. 2000), but no information
on possible change in duration of breeding season or
total seasonal productivity. Other reference: Freeman
and Crick (2002).
Tree Sparrow Passer montanus – National population decline has exceeded 95%. In local conservation
projects has benefited from provision of winter food
(small seeds) and nestboxes, especially when sited
near water, where insects are still plentiful (Field &
Anderson 2004). Showed increased nest success during
the years of decline, but no information on possible
changes in duration of breeding season or total seasonal productivity (Siriwardena et al. 2000).
Linnet Carduelis cannabina – Reduced survival and
nest success during the years of decline (Siriwardena
et al. 1999, 2000), but no information available on
possible change in duration of breeding season or on
total seasonal productivity. In a French study, annual
variations in production of fledglings influenced yearto-year population increase (Eybert et al. 1995). For
importance of oilseed rape as a food source, see
Moorcroft et al. (1997) and Moorcroft and Wilson
(2000).
Twite Carduelis flavirostris – Has suffered in
summer from loss of weeds from meadows near the
moorland edge (through improved grassland management), and in winter from loss of weeds from
arable land, and especially from loss of winter
feeding areas of coastal saltmarsh, which have been
converted to farmland (Atkinson 1998, Dierschke
2002). Additional reference: Brown et al. (1995).
Bullfinch Pyrrhula pyrrhula – Adverse habitat changes
involve loss of tall thick hedgerows from farmland
and loss of understorey shrubs from many deciduous
woods (often through increased deer browsing). These
changes also involve loss of food-plants, in addition
to loss of farmland weeds. Furthermore, recovery of
Sparrowhawk numbers may have confined Bullfinches
to feeding close to cover (through a behavioural
response), and thus reduced the total land area over
which they can forage, compared with the 1960s
(Newton 1967). The demographic cause of decline
is uncertain (Siriwardena et al. 2001), but higher nest
success was recorded during the decline (Siriwardena
et al. 2000), with no information on possible change
in duration of breeding season or total seasonal
productivity. The latter is greatly influenced by the
amount of late summer nesting (Table 1; Newton
1999, Proffitt et al. 2004).
Yellowhammer Emberiza citrinella – Breeding densities in different parts of Britain strongly correlated
597
with the proportion of land under arable crops, with
crop diversity and with hedgerow length. Decline
began later than in some other seed-eaters, and most
marked following loss of minority cereal crops from
western areas now dominated by grass and non-cereal
crops (Kyrkos 1997, Kyrkos et al. 1998). Individual
nest success was higher during years of population
decline (Siriwardena et al. 2000), but in one study
on nine scattered farms total seasonal productivity
was too low to maintain a stable population (Bradbury
et al. 2000).
Cirl Bunting Emberiza cirlus – Decline attributed
to lack of insect food for chicks in breeding season,
and seeds in winter. Appropriate conservation measures, within the framework of an agri-environment
scheme, promoted an increase in food-supplies, leading to a four-fold increase in the remnant population
within 10 years (Evans & Smith 1994, Evans 1997,
Wotton et al. 2000, Peach et al. 2001).
Reed Bunting Emberiza schoeniclus – Probably
suffered from both land drainage and destruction of
‘rank patches’ (reducing nesting habitat) and decline
in food supply (insects in summer, weed and grass
seeds in winter). During the years of decline (1975–
83) breeding numbers fell rapidly on arable and
mixed farms, but remained relatively stable on
pastoral farms (Peach et al. 1999). The decline was
greater in northern Britain than in the southeast.
Annual survival was lower during the years of decline
(Peach et al. 1999), as was nest success (Siriwardena
et al. 2000), and recent study suggests a decline in total
seasonal productivity in some areas (Brickle & Peach
2004). Oilseed rape crops and small wetland features
(such as ditches) now provide most nesting places in
farmland. Additional reference: Burton et al. (1999).
Corn Bunting Miliaria calandra – National population decline has exceeded 80%. Fewer birds now
raise a second brood than in the past, reducing the
seasonal production of young (Brickle & Harper
2002), but success per nesting attempt was recorded
as slightly higher during the years of decline (Crick
1997; Siriwardena et al. 1998). Nest survival was
lower in localities with little invertebrate chick food
(owing to pesticide use), which led to chick starvation and predation (Brickle et al. 2000). Population
decline in Schleswig-Holstein, Germany, was attributed to increased chick starvation (Busche 1989).
Benefits from low-input spring-sown cereals (barley),
associated weedy winter stubbles and wide field
margins. Other references: Donald and Evans (1994),
Brickle and Harper (1999), Crick (1997), Donald
and Forrest (1995), Donald et al. (1994).
© 2004 British Ornithologists’ Union, Ibis, 146, 579– 600
598
I. Newton
Turtle Dove Streptopelia turtur – Decline attributed
to reduction of tall hedgerows used for nesting and
weed-seeds used as food (Browne & Aebischer 2001).
Increased nest success recorded during the years of
decline (Siriwardena et al. 2000), but reductions in
duration of breeding season and in total seasonal
productivity (Browne & Aebischer 2001, 2003).
Skylark Alauda arvensis – Adverse habitat changes
include loss of rough grassland, switch from springsown to autumn-sown cereals (which grow too tall
for nesting in spring), and conversion of mixed farms
to cereal or intensive grass monocultures (Chamberlain
& Gregory 1999); food shortages involve summer
insects and winter seeds (Jenny 1990, Odderskaer
et al. 1997). Breeding densities tend to be higher in
permanent grass and set-aside than in autumn-sown
or spring-sown cereals (Poulsen et al. 1998; WakehamDawson et al. 1998, Chamberlain et al. 1999a, Eraud
& Boutin 2002); crops that do not favour breeding
Skylarks, such as autumn-sown cereals and rape, have
become increasingly prevalent in recent decades.
Nest success was higher during the years of decline
(Siriwardena et al. 2000), but several studies suggest
reduction in the duration of the breeding season,
because of earlier crop growth and lack of alternative
habitat locally (a consequence of greater arable
monoculture) (O’Connor & Shrubb 1986, Wilson
et al. 1997, Chamberlain & Crick 1999). No information on possible change in mortality. Breeding
densities and seasonal productivity increased following the provision of unsown patches (4-m squares
at two per hectare) in autumn-sown cereal fields
(Morris et al. 2004). Other references: Green (1978),
Shläpfer (1988), Donald et al. (2001a, 2002),
Robinson (2001), Pierce-Higgins and Grant (2002).
Meadow Pipit Anthus pratensis – In lowland, decline
associated with loss of patches of rough grass. In
upland, reduced breeding densities evident in heavily
grazed, shorter swards (Vanhinsberg & Chamberlain
2001, Pierce-Higgins & Grant 2002). Intensive grazing of heather moorland encourages the replacement
of heather by grass, which favours Meadow Pipits,
whose densities decline under further grazing, which
reduces sward height and diversity, and associated
insect densities (Smith et al. 2001). No relevant data
on demographic changes during the years of decline.
Yellow Wagtail Motacilla flava – Breeds in damp
grassland and in dry sparsely vegetated arable land
(Mason & Lyczynski 1980, Nelson 2001). Decline
attributed to drainage and reductions in the area of
damp grassland, and generally more intensive grassland
management, and to change from spring-sown to
© 2004 British Ornithologists’ Union, Ibis, 146, 579–600
autumn-sown crops. Decline most marked in pastoral
regions (Chamberlain & Fuller 2001). No published
information on possible change in reproductive or
mortality rates, or on possible effects on population
levels of events in African wintering areas. Yellow
Wagtails have responded with increased breeding
density to raised water levels in some grassland
nature reserves. Additional references: Bradbury and
Bradter (2004), Henderson et al. (2004).
Starling Sturnus vulgaris – Reduction of food supply caused by conversion of former grass to arable in
eastern districts, and by more intensive management
of grassland generally, leading to reduction in soil
invertebrates, and also by reduction in the numbers
of accessible feed-sites for farm stock. Reduced survival during the years of decline recorded for Britain,
and reduced reproductive rate recorded in Finland
(Tiainen et al. 1989). Other references: Feare (1994),
Whitehead et al. (1995), Freeman et al. (2002).
Blackbird Turdus merula – Decline associated
with loss of hedgerows and field boundaries, and
land drainage which reduces food availability. In
The Netherlands, the main demographic change was
reduced annual survival (Dix et al. 1998). Increased
breeding density and success followed various conservation measures (including predator control) at
the Game Conservancy Trust’s farm in Leicestershire
(Stoate & Szczur 2001).
Song Thrush Turdus philomelos – Decline associated
with loss of hedgerows and field boundaries, and
land drainage, which reduces food availability.
Main demographic cause assessed as reduced survival,
especially in years of prolonged summer drought
or winter frost (Baillie 1990, Thomson et al. 1997,
Robinson et al. 2004), judged as sufficient in a population model to account for decline at the observed
rate, without any concurrent change in reproduction
(Robinson et al. 2004). However, in one study, the
breeding season was shortened in a dry arable area,
compared to a more mixed farming area, leading to
reduction in seasonal production of young, also judged
as sufficient to cause population decline (Peach et al.
2004). Increased breeding density and success followed
various conservation measures (including predator
control) at the Game Conservancy Trust’s farm in
Leicestershire (Stoate & Szczur 2001).
Lapwing Vanellus vanellus – Main adverse habitat
change associated with the drainage of wet grassland
(Fig. 2); also conversion of mixed farms to arable
or ‘improved’ grass monocultures; change from
spring-sown to autumn-sown cereals (which reduces
the area of spring tillage, favoured for nesting); and
Recent declines of farmland bird populations in Britain
increased stocking densities on grassland (which leads
to more disturbance, nest predation and trampling)
(Beintema & Muskens 1987, Baines 1988, 1989,
Beintema 1988, Galbraith 1988, Shrubb 1990, Shrubb
& Lack 1991, Hudson et al. 1994, Wilson et al. 2001,
Hart et al. 2002). No change in annual survival during the years of decline (Peach et al. 1994), so
reduced reproduction proposed as the demographic
cause; and in some local populations annual production measured as insufficient to offset expected annual
mortality (e.g. Galbraith 1988). Seasonal productivity
lower on improved than on unimproved grassland,
owing to fewer replacement clutches and poorer
chick survival (Baines 1989). In some localities, single pairs and small groups are more vulnerable to egg
predation than larger groups, owing to the reduced
effectiveness of communal nest defence (Seymour
et al. 2003). Lapwings have responded with increased
breeding density to local reserve management and
agri-environment schemes (Ausden & Hirons 2002,
Bradbury & Allen 2003). Additional references: Baines
(1988, 1989), Crick et al. (1998), Shrubb (1990),
Henderson et al. (2001, 2003), Sheldon et al. (2004).
Snipe Gallinago gallinago – Main adverse habitat
change is the drainage of wet tussocky grassland (e.g.
Baines 1988). Even in some areas where birds still
breed, the nesting season is shortened because the
ground dries out earlier in the breeding season, leading to reduction in seasonal productivity (Green
1988a). Snipe have responded with increased breeding density to raised water levels in some grassland
nature reserves but not in others (Ausden & Hirons
2002). Two count schemes gave conflicting results,
BBS indicating an increase in recent years, and
breeding wader surveys in meadows a steep decline.
Additional reference: Crick et al. (1998).
Curlew Numenius arquata – Main adverse habitat
change is the drainage of rough wet grassland (e.g.
Baines 1988). High predation rates on eggs in some
areas, such as Northern Ireland, where measured
reproductive rates were too low to sustain populations and could account for recent rates of population decline (Grant et al. 1999). Fragmentation of
habitats may also allow Foxes to search nesting
places more efficiently. Other references: Berg (1992,
1994).
Redshank Tringa totanus – Main adverse habitat
change is drainage of wet grassland (e.g. Baines 1988).
On coastal saltmarsh, breeding densities declined
more markedly during 1985–96 on sites that had
experienced an increase in grazing pressure, from
ungrazed/lightly grazed to moderately/heavily grazed,
599
although some grazing by cattle was deemed beneficial
to sward structure (Norris et al. 1998). Redshanks
have responded with increased breeding density to
raised water levels in some grassland reserves (Ausden
& Hirons 2002).
Stone Curlew Burhinus oedicnemus – On arable
land, management has entailed finding nests, and
protecting them from farm machinery, and the
provision (through an agri-environment scheme) of
spring tillage for nesting (Aebischer et al. 2000). Other
references: Green (1988b), Green and Griffiths (1994).
Corncrake Crex crex – Main decline attributed to
earlier and mechanized grass cutting (Norris 1947),
but drainage and intensive grass management has
also removed much previously suitable nesting habitat (Stowe et al. 1993). One of the last remaining
populations of Corncrake in Ireland is in the
Shannon ‘callows’, where mowing is forced late
by unregulated winter and spring flooding (Shepherd
& Green 1994). Breeding success and breeding
density in various areas increased in response to later
and more careful grass cutting (Green & Stowe 1993,
Green et al. 1997, Green 1999, Green & Gibbons
2000).
Grey Partridge Perdix perdix – Population decline
has exceeded 85%. One of the most thoroughly
studied species, with proposed mechanisms tested by
experiment (Fig. 1, Potts 1986, Rands 1985, Potts &
Aebischer 1995, Tapper et al. 1996). Other references:
Green (1984), Bro et al. (2000).
Black Grouse Lyrurus tetrix – Heavy grazing of
moorland habitat causes decline in food-plants (for
full grown birds) and insects (for chicks) (Fig. 3;
Baines & Hudson 1995, Baines 1996, Jenkins &
Watson 2001). Local populations responded, with
improved breeding success and breeding densities, to
reduced grazing within the framework of an agrienvironment scheme, and some also responded in
the same way to predator control (Calladine et al.
2002, Warren & Baines 2004).
Red Grouse Lagopus l. scoticus – Predation by
raptors (especially Hen Harriers Circus cyaneus) can
cause substantial population decline (Redpath &
Thirgood 1997), but because some raptors and other
predators are controlled on most grouse moors, longterm declines in Red Grouse densities are more often
associated with loss of heather through overgrazing
(Redpath & Thirgood 1997, Jenkins & Watson 2001).
High sheep numbers in some areas also raise the incidence of louping ill, which is often lethal to grouse,
accounting for some local declines (Duncan et al.
1979, Hudson & Dobson 1991).
© 2004 British Ornithologists’ Union, Ibis, 146, 579– 600
600
I. Newton
Barn Owl Tyto alba – Main adverse habitat change
is the loss or overgrazing of rough grassland, which
supports the main prey species, the Field Vole Microtus
agrestis; also loss of nest-sites through hedgerow tree
removal and ‘barn conversion’, and collapse of old,
disused cottages, previously suitable (Shawyer 1987,
Ramsden 1998, Newton 2002). Population assessments
in 1982–85 and 1995–97 put national numbers at
4500 pairs and 4000 pairs, respectively, but numbers
fluctuate greatly from year to year, and the two figures
result from different methodology, so may not be
comparable (Shawyer 1987, Toms et al. 2001). Has
responded by increased density and breeding success
to the fencing out of sheep from areas of grassland
(as in afforestation projects), and by increased breed-
© 2004 British Ornithologists’ Union, Ibis, 146, 579–600
ing density to the provision of nestboxes in areas
with insufficient nest-sites (Newton 2002).
Sparrowhawk Accipiter nisus, Merlin Falco columbarius, Peregrine F. peregrinus – Main declines from
late 1950s to early 1960s, associated with the heavy
use of organochlorine pesticides (Fig. 4). Populations
recovered in subsequent decades following progressive reductions in organochlorine use, and their
replacement by less persistent insecticides (Newton
1979, 1986, Ratcliffe 1993, Newton et al. 1997,
1999). The Sparrowhawk has stabilized or may have
been in regional decline since about 1994.
Kestrel Falco tinnunculus – As for Barn Owl, except
that old buildings are much less important as nest-sites
(Village 1990).