Restoration of wet features for breeding waders on lowland grassland

Authors


Correspondence author. E-mail: s.eglington@uea.ac.uk

Summary

  • 1Over the last century, the loss of around half of the world's wetlands, principally through drainage and conversion to agriculture, has been one of the main drivers of declines in breeding waders. Across Europe, nature reserves have been effective conservation islands for breeding waders, but management of the wider countryside is needed for more wide-scale population recovery. This is likely to require the restoration of wet features, but in a manner which is compatible with farming operations.
  • 2Here we explore the extent to which three types of wet feature influence the distribution of breeding lapwings Vanellus vanellus and their chicks on grassland. Footdrains are shallow channels used historically for drainage, but which can also be created and managed for water retention and cause little disruption to farming activities. Footdrain floods are areas where water overtops footdrains. Isolated pools are unmanaged areas of surface water resulting from rainfall or high water tables.
  • 3We selected 70 fields on nine sites which spanned the range of wet feature type and cover in early April. By May, only around 10% of the water within isolated pools remained, whereas 30–40% water was maintained in footdrains into June.
  • 4Fields with high footdrain flood densities attracted significantly higher densities of nesting lapwing and nests were more likely to be within 50 m of footdrain floods. Later in the season, footdrains were the primary remaining water source, and chick field use increased significantly with footdrain density. Chicks were also more likely to forage nearer footdrain floods in areas of wet mud created by receding water levels.
  • 5Synthesis and applications. Areas of shallow, small-scale flooding are of critical importance for breeding waders. Management tools such as footdrains, coupled with appropriate hydrological management, provide a means of retaining water throughout the breeding season. Installation of these features is relatively simple, but maintaining sufficient water levels within the system is critical, especially in the face of increasingly unpredictable water supplies associated with climate change. Such management tools offer a solution that may be both effective at improving breeding wader populations and practicable for commercial grazing marsh management.

Introduction

Since 1900, around half of the world's wetland habitat has been lost (Dugan 1993) and wetlands are now among the most degraded of all ecosystems (Amezaga, Santamaria & Green 2002). By 1985, an estimated 56–65% of inland water systems had already been drained for agriculture in Europe and North America, and losses have also been high in Asia, where extensive peatlands have been drained to increase the area available for livestock (Millennium Ecosystem Assessment 2005). Climate change puts further pressure on the remaining wetlands (Hulme 2005). Sea level rise is expected to result in a direct loss of coastal grazing marsh, while increased frequency of spring flooding or droughts is likely to have a detrimental effect on the habitat suitability of those grazing marshes that remain (Nicholls, Hoozemans & Marchand 1999; Smart & Gill 2003; Watkinson, Gill & Hulme 2004). Suggested mitigation for these losses has included the creation of replacement freshwater habitats elsewhere long before existing sites are lost, as well as better management of the habitat that remains (Wilson, Ausden & Milsom 2004).

Primarily as a result of this habitat loss and degradation, populations of grassland breeding waders have also undergone severe declines throughout Europe during recent decades (Hudson, Tucker & Fuller 1994; Henderson et al. 2002; Wilson et al. 2005). These declines have been associated with the increased intensity of agricultural management over the last 50 years (Newton 2004; Vickery et al. 2001; Wilson et al. 2004). The conversion to intensively managed, improved grassland is likely to have reduced both the area and the suitability of pastoral habitats (Wilson, Vickery & Browne 2001) and farmed grassland is usually an unsuitable breeding habitat for waders (Shrubb 1994).

The distribution of waders is generally related strongly to site wetness, and the lowering of water tables has frequently been found to adversely affect breeding wader populations (Green & Robins 1993; Vickery et al. 1997; Paillisson, Reeber & Marion 2002). On grazing marshes, maintenance of a mosaic of unflooded grassland and shallow areas of surface water helps to ensure that good nesting habitat and profitable feeding areas are present throughout the breeding season (Ausden & Treweek 1995; Ausden, Sutherland & James 2001). Raised water levels keep the surface soil soft and moist, which is especially important for probing snipe Gallinago gallinago and black-tailed godwit Limosa limosa (Green 1988), and keep soil invertebrates close to the surface, thus increasing their availability to surface-feeding birds such as lapwing (Ausden et al. 2001). Surface and soil water can also suppress vegetation growth (Ausden et al. 2001) and short vegetation can improve prey availability and detectability (McKeever 2003; Butler & Gillings 2004; Devereux et al. 2004). In addition, shallow areas of surface water are important foraging areas for chicks, providing a source of aquatic prey which would not otherwise be available (Ausden et al. 2001).

There are many challenges in providing the conditions required by breeding waders on commercial grazing marshes in the wider countryside, and government agri-environment schemes for breeding waders have had questionable success (Ausden & Hirons 2002; Kleijn et al. 2006; Verhulst, Kleijn & Berendse 2007). In particular, the provision of areas of flooding can be a serious source of conflict between management for conservation and commercial management. Uptake of past agri-environment schemes on lowland wet grassland has been low within the United Kingdom, because those options in which prescribed water levels were suitable for encouraging breeding waders were considered too extreme by many farmers (Ausden & Hirons 2002). Widespread surface flooding can result in extensive sward death (Ausden et al. 2001), making it unattractive to farmers in terms of forage production, and the soft soil caused by extensive flooding can also hinder movement of livestock and machinery. In addition, the production of short heterogeneous swards is often not compatible with the vegetation height and structure appropriate to hay, silage or livestock production (Vickery et al. 1997, 2001). Low-input livestock systems are thus likely to be central to providing the sward required by breeding waders (Vickery et al. 2001).

In this paper, we focus on the use of shallow wet features as a management tool for improving the grassland habitat of breeding waders, using the lapwing as a model species. Grasslands represent an increasingly important habitat for lapwings (Wilson et al. 2001), as the growth in autumn-sown crops has severely decreased the suitability of arable farmland for ground-nesting waders (Galbraith 1988; Berg et al. 2002). In particular, this work examines the role of three different types of wet features that vary in the extent to which they can be created and managed in influencing wader breeding distribution and success: (1) shallow channels historically used for drainage, known locally as ‘footdrains’; (2) areas of surface flooding resulting from water spilling over from footdrains, called here ‘footdrain floods’; and (3) isolated areas of surface flooding, termed here ‘isolated pools’. Land managers have little control over isolated pools as they form naturally from pluvial flooding in depressions within fields. However, by maintaining higher water levels in surrounding ditches, footdrains can be managed to create localized and controlled flooding within the footdrains and their associated footdrain floods in the spring, and to maintain this water into the breeding season. The key valuable characteristic of footdrains is that they cause little disruption to commercial management activities, such as livestock management and sward production, and allow for a high level of control over surface flooding. As such, footdrains may offer the opportunity to create a restricted flooding regime suitable for breeding waders that could also be acceptable to farmers (Milsom et al. 2002). However, the conservation value of footdrains will depend on whether they are attractive to nesting waders and foraging chicks. In this study, we therefore assess (1) whether lapwing nesting distribution is influenced by cover of the three wet feature types; (2) how water retention throughout the breeding season varies among wet feature types; and (3) how chick use of wet feature types varies and how this is influenced by water levels within the wet features.

Methods

study sites

The study was carried out on managed grasslands within the Broads Environmentally Sensitive Area (ESA) (52°35′ N, 01°35′ E, National Grid reference TG40) in eastern England from March to July 2005 and 2006. The Broads ESA is one of the few remaining large areas of wet grassland in Britain, extending over 43 000 hectares of river valley, grazing marsh and fen. While the Broads themselves (i.e. man-made shallow lakes) are a highly individual feature of eastern England, their associated grasslands are typical of those found throughout lowland Europe.

Nine study sites were selected within this area, comprising four sites managed by conservation organizations and five managed by commercial landowners. All sites were grazed with livestock (mean ± SE sward height 2·68 ± 0·21 cm) and had at least some level of water control. One site, Norton, is owned by a commercial landowner but managed intensively for nature conservation purposes under agri-environment schemes. This site comprises a small proportion of the landowner's total estate (four fields) and is surrounded predominantly by arable land. It has very high densities of wet features and a very effective predator control programme, and is thus more similar to nature reserves than to commercial farmland.

Seventy focal fields were selected from across the nine study sites to provide a wide range of wet feature densities (Table 1). Lapwing densities across the nine study sites were similar to those reported elsewhere in Europe (Table 2; Ausden & Hirons 2002; Salek & Smilauer 2002; Ottvall & Smith 2006).

Table 1.  The number of focal fields together with wet feature densities in April 2006 at each study site
ManagementSiteNo. fieldsMean (± SE) field size (ha)Mean (± SE) length footdrain (m ha−1)Mean (± SE) area footdrain flood (m2ha−1)Mean (± SE) area isolated pool (m2ha−1)
CommercialBranch Road56·04 ± 0·40108 ± 1911 ± 727 ± 9
CommercialHalvergate44·89 ± 0·59139 ± 31211 ± 10128 ± 23
CommercialNew Road54·27 ± 0·989 ± 3535 ± 270 ± 0
CommercialNorton47·68 ± 2·1785 ± 816745 ± 903250 ± 8
CommercialSt Benet's Levels55·42 ± 0·36166 ± 212 ± 2< 1 ± < 1
ConservationBerney174·85 ± 0·30151 ± 211060 ± 232131 ± 31
ConservationBerney new193·52 ± 0·2636 ± 429 ± 1755 ± 90
ConservationBuckenham65·75 ± 1·35171 ± 35288 ± 117604 ± 417
ConservationCantley56·07 ± 0·97104 ± 27279 ± 160400 ± 212
Total 70    
Table 2.  Mean densities of breeding lapwings across nine grassland sites within the Broads Environmentally Sensitive Area, 2006
SiteMean pair density (± SE) ha−1
Halvergate0·23 ± 0·08
Berney0·49 ± 0·15
Buckenham0·78 ± 0·28
Cantley0·22 ± 0·15
Branch Road0
New Road0·03 ± 0·003
Norton1·69 ± 0·48
St Benet's Levels0·28 ± 0·17
Berney new0·03 ± 0·02

grazing marsh habitat surveys

Prenesting surveys of habitat structure were carried out between 15 March and 15 April 2005 and 2006. Two transects (one on each diagonal) were undertaken on each of the 70 focal fields (mean transect length ± SE = 364 ± 9 m). Ten sampling points were located at equal distances along the length of each transect, giving a total of 20 samples per field. These surveys were repeated every month until July.

Along each transect, vegetation characteristics and ground conditions were measured (Table 3). At each point, six replicate measures of vegetation height were recorded to the nearest centimetre using a sward stick with a plastic disc (Stewart, Bourn & Thomas 2001) and the percentage surface cover of wet bare ground was also recorded using a 50 × 50 cm quadrat.

Table 3.  The names, unit of measurement and description of habitat variables recorded during surveys of fields and nest sites of breeding lapwing and locations of foraging chicks, on grazing marshes in the Broads, UK. Analysis column indicates variables used for different analyses (fn = field scale, nest placement; fc = field scale, chick use; wn = within field, nest placement; wc = within field, chick location). See text for details
Habitat variableUnitAnalysisDescription
Vegetation heightcmfn, fc, wn, wcRecorded to the nearest 0·5 cm, using a sward stick with a plastic disc
Wet bare ground% coverfn, fc, wn, wcUnvegetated damp or wet ground
Distance to wet featuremwn, wcDistance from a nest, chick or regular sampling point to the nearest footdrain, isolated pool or footdrain flood
Footdrain densitym ha−1fn, fcDensity of all footdrains within a field
Area of isolated pool/footdrain floodm2 ha−1fn, fcDensity of all isolated pools or flooded footdrains within a field
EpisodecategorywcSampling period from which data were taken

wet feature mapping and surveys

Footdrains within each field were digitized on MapInfo geographic information system (GIS) maps produced from aerial photographs using the Millennium Map 2000. These were checked in the field and any inaccuracies were corrected. At the start of the season, the location of all isolated pools and footdrain floods was mapped in the field using a global positioning system (GPS) and then digitized within MapInfo. Pools were classed as isolated areas of surface water. Footdrain floods were classed as areas of surface flooding resulting from water overtopping the banks of a footdrain. These maps were used to calculate the mean distance to wet features within a field. Grids marking out 20 regular sampling points were over-laid onto the wet feature maps and the distance of the grid points to each type of wet feature was calculated. In instances where no wet features were present within a field, the distance from the mid-point of the field to the nearest field edge was recorded.

The percentage cover of water within wet features was surveyed on a monthly basis. For footdrains, percentage cover was estimated as the maximum between the top of the banks of the footdrain. For isolated pools and footdrain floods, the edge of the feature was taken as the limit of the highest water level at any sample date and the percentage water cover within this limit was estimated. As the water receded, the position of the highest water levels remained visible from the structure of the sward.

lapwing nest-site characteristics

Nests were located by scanning the surrounding grazing marsh from a vehicle. Nest locations were marked and the surrounding habitat characteristics were measured as soon as each nest was located. Vegetation height was measured at six points of a hexagon 1 m around the nest and the percentage cover of wet bare ground was measured within a 50 × 50 cm quadrat placed immediately adjacent to the nest. The number of paces from the nest to the nearest of all three wet feature types (footdrains, isolated pools and footdrain floods) was recorded.

chick field and habitat use

Each study field was visited at least once a week and scanned for a period of 10 min from a vantage point overlooking the entire field to locate any adult lapwing present. All adults were observed to determine whether they were performing parental behaviour, such as brooding, leading or guarding chicks and, if so, attention was focused upon these birds to locate the brood. This method reduces the risk of sampling only easily located chicks, or of introducing bias by focusing search effort along wet features. The number of pairs displaying parental behaviour located within the 10-min sampling period in each field was used as a measure of brood density.

To compare levels of use of different fields by lapwing chicks, the number of brood-days day−1 was calculated. The number of broods in each field on days when fields were not surveyed was estimated using the midpoint assumption (Mayfield 1961); the first half of the between-survey interval is assigned the number of broods from the first count and the latter half is assigned the number from the second count. The cumulative total of these counts is then divided by the number of days between the first and last count on each field. The number of chicks in a brood was not taken into account.

The initial observed location of all broods was used as the point from which habitat variables were collected. The distance from that point to the nearest footdrain, pool and footdrain flood was recorded, along with six replicated measurements of vegetation height and the percentage of wet bare ground.

The habitat structure around chick locations was then compared to the overall habitat structure within each field, as recorded during the May and June habitat surveys, as this was the main period during which chicks were present. The densities of footdrain floods and isolated pools were recalculated for each survey, based on the estimates of percent water cover within each wet feature.

data analysis

Due to the drawbacks of stepwise multiple regression (see Whittingham et al. 2006), a full model approach was used and all relevant predictors were included in the model and reported. A carefully considered suite of predictors was used for each model, based on our original hypotheses. We hypothesized that wet features would be an important habitat characteristic for breeding lapwing, so all models included information on each of the three wet feature types. Previous research has shown that vegetation height is important for breeding waders (Vickery et al. 1997; Milsom et al. 2000; Butler & Gillings 2004), so this was also included within the models, as was the percentage cover of wet bare ground which is thought to be an important feeding habitat (Green & Cadbury 1987; Joiner 2002; Taylor 2004). Field size was included within analyses of adult nesting field choice, as avoidance of boundaries would increase the attractiveness of larger fields (Whittingham, Percival & Brown 2000).

For the analysis of adult choice of nesting field (among-field scale), a generalized linear model (GLM) with a logit link function and a binomial error term was used to identify the characteristics of fields where breeding lapwing were either present or absent. This method was also used for a within-field spatial analysis of the distribution of nests in occupied fields. These were performed using proc genmod in sas (SAS 2004).

A GLM with a log-link function and a Poisson error term was used to classify which habitat characteristics were important in determining the density of breeding lapwing within occupied fields. Number of pairs was used as the dependent variable and the natural logarithm of field area was offset in the models to control for the greater probability of more pairs being present in larger fields.

To analyse variation in chick use of occupied fields at the among-field scale, data were analysed in a GLM with a log link function, a Poisson error term and the natural logarithm of area as an offset variable.

For the analysis of chick distribution at the within-field spatial scale, an additional variable called ‘episode’ was included in the model, to account for any variation that may have arisen due to changing habitat conditions through the season. Each habitat survey represented a sampling episode (the 14-day period either side of each habitat survey). For each episode, the habitat structure around chick locations was compared to overall field habitat structure from the survey during that sampling period. Episodes were numbered 1–4 and this variable was retained in the model, regardless of significance, to account for any temporal variation in habitat structure.

For all models, site was specified as a fixed factor categorical variable and this was retained in the model as a blocking factor, regardless of significance, to account for any differences that might be attributable to variations between sites.

Results

wader breeding densities

Densities of nesting lapwing across the nine sites varied significantly from zero pairs at Branch Road to 1·69 pairs ha−1 at Norton, with a mean of 0·34 ± 0·07 standard error (SE) pairs ha−1 (H8 = 34·22, P < 0·0001, Table 2).

water levels in wet feature types

Rates of evaporation and drainage over the season varied greatly across the three types of wet feature (Fig. 1). Isolated pools retained only c. 10% of their water by as early as May, and had decreased in number by around 65%. By contrast, footdrains retained their water much more effectively and by June, when chick numbers were at their highest, c. 70–80% of footdrains and footdrain floods were still present and contained c. 40% water cover. By the end of the breeding season in July, all three types of wet feature held < 10% of maximum water levels, although there were still around 25% of footdrains and footdrain floods that contained at least some water.

Figure 1.

Changes in (a) percentage cover of water in wet features (means ± SE) and (b) proportion of the total number of wet features containing any water in footdrains (grey solid lines), footdrain floods (black solid lines) and isolated pools (grey broken lines) across 70 fields in the Broads, from April to July 2006.

factors affecting nesting field selection

The probability of a field being occupied by breeding lapwing was significantly greater when there was a higher density of footdrain floods (Fig. 2, Table 4). Across the densities of wet features in this study, fields with footdrain flood densities over 300 m2 ha−1 were more likely to be occupied by nesting lapwing than fields with lower footdrain flood densities. None of the other variables had a significant effect within this model, apart from the blocking factor identifying site (Table 4), which is due largely to the unusually high nesting densities in all fields at Norton (see Methods for details of this site).

Figure 2.

The probability of fields containing breeding lapwing in relation to footdrain flood density. For statistics, see Table 4. Bars show the frequency distribution of the observed data for occupied (white bars) and unoccupied (grey bars) locations and the line shows the fitted logistic regression curve (see Smart et al. 2004).

Table 4.  Results of generalized linear models of the effect of five habitat variables (see Table 3 for definitions) on nesting field selection by adult lapwing, densities of nesting lapwings on fields and chick use of fields (*P < 0·05, **P < 0·01, ***P < 0·001). Note that the degrees of freedom connected with site is specific to each analysis (A = adult field selection, D = density within fields, C = chick field use)
 d.f.Adult field selection χ2Density within fields χ2Chick field use χ2
Footdrain density13·160·884·33*
Footdrain flood density18·91**4·78*0·44
Pool density12·450·050·20
Percentage wet mud11·300·440·01
Field size1< 0·01
Vegetation height12·970·210·39
Site7 (A), 7 (D), 6 (C)15·78*23·12**16·87**

factors affecting lapwing nesting density on grazing marshes

There was a significant, positive relationship between the density of footdrain floods and breeding lapwing density among fields (Fig. 3). However, there was also a large degree of variance in nesting densities for any given density of footdrain floods. Again, due to the influence of Norton, the effect of site was highly significant within the model (Table 4) and this was the only other significant variable.

Figure 3.

The relationship between the density of breeding lapwing pairs and the density of footdrain floods on 31 grassland fields in Norfolk (Y = 5·57x + 0·47, R2 = 0·38, P < 0·05).

factors influencing the distribution of chicks between fields

The number of brood-days day−1 across 60 fields was significantly influenced by footdrain density, and varied significantly among sites (Table 4). There was a weak trend for fields with a higher footdrain density to have a greater number of brood-days day−1 (Fig. 4) and, as outlined above, the high nesting densities and productivity at Norton are the cause of the significant site effect.

Figure 4.

The relationship between footdrain density and the number of lapwing brood-days on 60 fields in Norfolk (Y = 0·0036x + 0·07, R2 = 0·12, P < 0·001).

factors influencing nest site selection within fields

Across all sites, there was a significant, but weak, tendency for nests to be located close to footdrain floods, but clearly nests can be located anywhere up to 100 m from these wet features (Fig. 5, Table 5).

Figure 5.

The effect of distance to the nearest footdrain flood on the location of lapwing nests. For statistics, see Table 5. Bars show the frequency distribution of the observed data for occupied (white bars) and unoccupied (grey bars) locations and the line shows the fitted logistic regression curve.

Table 5.  Results of generalized linear models of the effect of five habitat variables (see Table 3 for definitions) on nest site selection by adult lapwing, and foraging locations of lapwing chicks (*P < 0·05, **P < 0·01, ***P < 0·001). Note that the degrees of freedom connected with site is specific to each analysis (N = nest, C = chick)
 d.f.Nests χ2Chicks χ2
Distance to footdrain10·011·00
Distance to footdrain flood16·69**4·09*
Distance to pool11·48< 0·01
Percentage wet mud10·9313·38***
Vegetation height12·1923·34***
Site7 (N), 6 (C)2·398·94
Episode3NA6·67

factors influencing the distribution of chicks within fields

Chicks were significantly more likely to be located in areas with shorter vegetation that were closer to footdrain floods and which had a greater percentage cover of wet bare ground (Fig. 6, Table 5). Chicks were never recorded in vegetation longer than 10 cm (Fig. 6a) and almost half of all located chicks were foraging within footdrain floods (Fig. 6b). Over half the foraging chicks were also in areas with a high percentage cover of bare wet mud, despite this being a rarely encountered habitat type within these fields (Fig. 6c)

Figure 6.

 The influence of (a) vegetation height, (b) mean distance to footdrain flood and (c) percentage wet bare ground on the probability of a lapwing chick being located at points within a field. For statistics see Table 5. Bars show the frequency distribution of the observed data for occupied (white bars) and unoccupied (grey bars) locations and lines show the fitted logistic regression curves.

Discussion

This study has demonstrated that temporal and spatial variation in the density and water content of wet features has a major impact on the distribution of breeding lapwing. The importance of different types of wet features varies through the breeding season; isolated pools hold large amounts of water at the start of the breeding season but dry out rapidly and had no impact on the distribution of lapwing nests or chicks. In contrast, the density of footdrain floods is of primary importance when lapwing are selecting nesting fields (Figs 2 and 3), and nests and chicks are more likely to be located nearer to footdrain floods (Figs 5 and 6). Moreover, broods tended to be concentrated in fields with a higher density of footdrains (Fig. 4), and within those fields they foraged in areas of wet bare ground and with short vegetation (Fig. 6), which were often associated with footdrains and areas that had been footdrain floods prior to evaporation. Controlled flooding with techniques such as footdrains therefore offer some hope as a means of potentially aiding wader population recovery in the wider countryside.

Within the European Union, agri-environment schemes provide a means of recreating and restoring wetland habitats but their success so far has been limited (Kleijn & Sutherland 2003; Kleijn et al. 2006), often because the management recommendations, particularly in relation to water levels, are inadequate (Berg et al. 2002; Verhulst et al. 2007; Kahlert et al. in press). Raising ground water levels is often unpopular with farmers, but the controlled flooding techniques that we have explored here may prove acceptable to farmers in lowland areas throughout Europe and elsewhere.

wet features and breeding waders

The association between breeding lapwing and footdrains demonstrated in this study suggests that such managed wet features can provide a substitute for the high water levels and extensive surface flooding that has been found to be important for several other species of breeding wader (Green & Robins 1993; Caldow, Pearson & Rose 1997; Vickery et al. 1997). Wet features provide feeding areas for breeding waders (Green & Cadbury 1987; Ausden et al. 2001; Milsom et al. 2002), and previous studies have found that foraging rates were higher in this habitat (Milsom et al. 2002; Devereux et al. 2004). Wet features create areas of reduced vegetation growth which can increase foraging rates through greater accessibility and availability of prey (Butler & Gillings 2004; McCracken & Tallowin 2004). They also provide a supply of aquatic invertebrates (Ausden et al. 2001), which are an important food source for chicks, the importance of which increases as the season progresses (Ausden et al. 2003). The soft sediments within wet features also offer the advantage that they are likely to be more penetrable to the bills of probing waders (Milsom et al. 2002), thus increasing feeding opportunities.

The association between nests and wet features found in this and other work (Joiner 2002; Milsom et al. 2002; McKeever 2003; Smart et al. 2006) may be due to adults selecting nest sites based primarily on foraging habitat requirements of chicks. Chick mortality increases with the distance over which they have to travel from the nest to foraging areas (Galbraith 1988), so by nesting close to wet features adults may be minimizing the distance chicks have to travel to reach high-quality foraging areas (Berg 1993, 1994). The distances involved at this scale are small but, for newly hatched chicks, a good food supply in the immediate vicinity may be vital. The high energetic demands placed on precocial chicks mean that habitat selection and the associated dietary options can be critical for their survival (Pearce-Higgins & Yalden 2004).

It is interesting to note that chicks tend to spend more time in fields with a higher density of footdrains (Fig. 4) yet, within these fields, they have a tendency to forage closer to footdrain floods, as opposed to the footdrains themselves (Fig. 6b). This may be because evaporation of water from footdrain floods resulted frequently in areas of wet bare mud within which chicks often foraged. In addition, the flat nature of footdrain floods may allow better visibility of the surrounding land than is possible from within a footdrain.

The importance of landscape structure in influencing wader breeding distribution is indicated in Figs 3 and 4. Although fields with high footdrain densities are clearly preferred, the numbers of lapwing nests and broods can vary greatly for any given footdrain density. This variation is likely to be a consequence of differences in the landscape surrounding individual fields; four of the fields in which nesting densities and chick use were highest (and higher than predicted from wet feature density) were from one site (Norton). As described in the Methods, this is a very small site with extensive wet features which is set within a largely intensively managed arable landscape. Conversely, the fields with high wet feature densities but lower than predicted breeding densities and levels of chick use tend to be on a large and well-managed nature reserve (Berney) on which breeding territories can be more dispersed. Identifying key areas for habitat restoration for breeding waders (and any associated targeted funding initiatives) may therefore require a more detailed exploration of the role of landscape structure.

implications for habitat management and restoration

On lowland wet grassland sites where it is possible to maintain raised water levels, footdrains and their associated flooding offer a workable management tool to provide suitable conditions for breeding waders.

In many instances, surface wetness can be increased by raising water tables through manipulation of water levels in ditches (Armstrong 1993, 2000). However, the hydrological response to raising water levels in ditches varies with the soil type influence on the lateral movement of water. Clay soils have low hydraulic conductivity, so management of the water table cannot be coupled closely with ditch levels. Consequently, maintaining high water levels in ditches does not necessarily maintain wetness over the interior of the fields (Armstrong 1993, 2000), and surface flooding is generally required to provide foraging areas for breeding waders (Benstead et al. 1997). In contrast, peat soils have a much higher hydraulic conductivity so maintenance of a high water table is of crucial importance for creating surface wetness across the land.

Many farmers are understandably reluctant to allow extensive flooding on their land (Ausden & Hirons 2002), and prolonged flooding can also result in a reduction in invertebrate numbers (Ausden et al. 2001). As such, the restricted flooding regime provided by a system of footdrains and their associated floods can allow manipulation of ditch water levels to maintain flooding in wet features throughout the breeding season, while leaving most of the land free from inundation. By using a system of pumps and sluices, water levels can be raised in surrounding ditches and fed out into the centre of the fields using footdrains, which act effectively as linear pools. If water levels are raised sufficiently, the resulting over-topping of footdrains causes the formation of the wider areas of surface flooding which lapwing and other breeding waders favour. The area over which footdrain floods extend can be controlled through locating footdrains in low-lying areas of fields and selecting appropriate ditch water levels. It is also possible to design areas for over-topping by creating a scrape around a section of the footdrain.

Maintaining appropriate levels of water control will, however, be increasingly difficult in the face of future climate change and the predicted increase in frequency of periods of both flooding and drought (Nicholls et al. Marchand 1999; Watkinson et al. 2004). Footdrains provide a potential means of retaining water during drought periods and draining excess water during floods. Thus this technology may provide valuable control over increasingly unpredictable water supplies.

Careful consideration of the location and hydrological management of new footdrains is, however, essential. Footdrains were used historically for drainage and if water levels in surrounding ditches are not kept high enough, they can actually reduce the wetness of fields through drainage. Maintaining water within footdrains is also extremely difficult if they are located in the higher parts of fields, which would limit their use as a conservation tool and hinder farming operations.

wet features and the wider countryside

A significant barrier in developing management responses to limit further deterioration of wetlands is unwillingness to undertake effective actions (Millennium Ecosystem Assessment 2005). Existing management advice for non-reserves is not designed to optimize the management of wet grassland for both livestock rearing and biodiversity conservation (Milsom et al. 2000). Therefore, mechanisms to help landowners to improve the biodiversity value of land whilst maintaining commercial farming operations are required.

Throughout Europe, there are two main systems available to aid conservation of breeding waders: management on nature reserves and management of the wider countryside through agri-environment schemes (Baillie et al. 2000; Ausden & Hirons 2002). Nature reserves usually seek to maximize biodiversity within a defined area of the countryside and often act as refuges for declining species (Ausden & Hirons 2002). However, abundance of species within high quality patches of habitat is often dependent not only upon processes within that patch but also upon processes within the surrounding habitats (Baillie et al. 2000). As such, conserving small pockets of high quality habitats within reserves is unlikely to be enough to conserve declining populations. Improved management of the wider countryside is also necessary (Ausden & Hirons 2002; Henderson et al. 2002).

A key aspect of agri-environment schemes is their potential for a landscape-scale approach to countryside management (Dolman, Lovett & O’Riordan 2001), which may avoid the problems of creating isolated fragments of high-quality habitat described by Benton et al. (2002) and Benton, Vickery & Wilson (2003). Current options within agri-environment schemes in the United Kingdom provide opportunities for maintenance, restoration and creation of wet grassland for breeding waders, and an integral part of these involves water level management. Footdrains and their associated flooding offer the potential to create conditions that are suitable for breeding waders within the wider countryside while enabling management for commercial purposes to continue.

In the current climate of changing agricultural support mechanisms across Europe and the newly developed agri-environment schemes in the United Kingdom, there is scope to include further support for the installation and management of features such as footdrains in new schemes as they evolve. The policy approaches being developed in the current phase of post-industrial agriculture have the potential to steer agriculture in directions that may help to the reverse the declines in biodiversity (Buckwell & Armstrong-Brown 2004). However, biodiversity and agriculture can only be reconciled in the context of more sustainable land management systems (Firbank 2005), and agri-environment schemes will work only if the management prescriptions are tailored to the ecological needs of target taxa (Bradbury & Allen 2003) and are commensurate with modern farming techniques. With the appropriate financial support and management advice, footdrains and their associated floods could provide a workable tool for farmers to aid the recovery of breeding waders.

Acknowledgements

This work was funded by the Natural Environment Research Council, and Natural England together with the Royal Society for the Protection of Birds through the Action for Birds in England Partnership. Thanks to the landowners for access and to Jutta Leyrer and Fiona Burns for their assistance in the field.

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