Dr Andrew Hoodless, Head of Wetland Research
Breeding wader declines: a pan-European issue
Along with many other farmland birds, breeding waders have been declining across Europe for at least the last 30 years. This is primarily due to agricultural improvement of their favoured wet grassland habitats, involving drainage, fertilization of grass swards and increases in livestock densities. Agri-environment schemes in several countries have attempted to address these problems by compensating farmers for maintaining higher field water levels and practising lower intensity farming. However, there is an increasing body of evidence from scientific studies conducted on breeding waders across Europe that high levels of predation by widespread, generalist predators is likely to be limiting wader population recovery in many situations.
There is good evidence from several countries for increases in the numbers of generalist predators such as foxes and corvids over the last 30 years, leading to the situation where in many cases habitat restoration alone may not be sufficient to recover wader populations. Analysis of lapwing adult survival rate indicated no appreciable change during 1960-1990 and suggests that insufficient productivity is the main driver of lapwing declines.
The decline of waders in the Avon Valley
The River Avon develops into a large calcareous lowland river south of Salisbury, which is of national and international importance for its wildlife communities. The floodplain consists of humid, species-rich grassland, with ditches and some standing water usually persisting through the spring months.
There are still limited areas of diverse MG8 (Cynosurus cristatus-Caltha palustris) swards, supporting species such as brown sedge (Carex disticha), fen bedstraw (Galium uliginosum), water avens (Geum rivale) and marsh valerian (Valeriana dioica). The floodplain SPA and SSSI designations reflect its value for a wide range of species, including breeding waders, wintering wildfowl and waders (Bewick’s swans (Cygnus columbianus), gadwall (Anas strepera), wigeon (Anas penelope), white-fronted geese (Anser albifrons) and black-tailed godwits (Limosa limosa)), otters (Lutra lutra) and certain insects (scarce chaser dragonfly (Libellula fulva)), molluscs (Desmoulin’s whorl snail (Vertigo moulinsiana), Valvata macrostoma and the pea mussel (Pisidium tenuilineatum)) and plants (mudwort (Limosella aquatica), frogbit (Hydrocharis morsus-ranae), small fleabane (Pulicaria vulgaris)) of national importance. The traditional farming pattern of the valley reflects the propensity for winter flooding, with relatively low-intensity livestock farms and a predominance of grazed pastures and hay fields.
The Avon Valley has historically supported nationally important populations of breeding Northern lapwing (Vanellus vanellus), redshank (Tringa totanus) and common snipe (Gallinago gallinago). In common with other lowland wet grassland sites throughout Britain, the numbers of breeding waders in the Avon Valley have declined dramatically since the early 1980s, with declines of 64% in lapwing, 75% in redshank and 97% in snipe during 1982-2002. The Avon Valley was designated as an Environmentally Sensitive Area (ESA) in 1993. Since 2003, farmers have been encouraged to join the Higher Level Stewardship (HLS) scheme, and uptake by farmers within the valley has been high. In total, this amounts to a considerable investment in habitat restoration over the last 20 years, but to date there has been no reversal of the trend in wader numbers.
The GWCT has been involved in monitoring breeding waders in the Avon Valley for over 20 years. We hold quantitative data on field conditions and wader numbers and distribution on sites with breeding waders in the Avon Valley in four years: 1990, 1996, 2003 and 2010. Since 2007, we have collected data on lapwing breeding success on 15 farms. Our data for 2007-2013 show clearly that poor breeding success is driving the decline in lapwings and that low nest survival resulting from high levels of predation is the key issue. Lapwing productivity in the Avon Valley has averaged 0.41 fledged young per pair, reaching a maximum of 0.69 in just one year: this is considerably below the threshold average of 0.70 fledged young per pair per annum needed to maintain a stable population. This is similar to the situation documented in other parts of the UK, e.g. the Norfolk Broads, and in the Netherlands, where mammalian predation on lapwing nests has been recorded at levels where it is limiting population growth.
Priority issues in the Avon Valley
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High levels of nest predation
GWCT data for lapwings in the Avon Valley provide evidence for high levels of nest predation. Our data indicate that 61% of nesting attempts fail and that 82% of nest failure is caused by predation. Information on the timing of predation events from temperature loggers placed in nests indicates that 41% of nest predation is during daylight hours and hence can most likely be attributed to corvids or gulls, with 49% of predation at night, mainly by fox, and 10% during twilight at dawn and dusk.
Lapwing brood survival in the Avon Valley over the last seven years has averaged 35%. We do not have good information on the causes of chick mortality, but published studies from the Netherlands suggest that predation is the main cause and that a range of predators from herons and buzzards to stoats are implicated.
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Inappropriate water levels and sward conditions
Currently, inappropriate water levels and an increasing polarization of sward conditions towards intensively grazed short swards or rank areas with scrub encroachment are the most pertinent habitat issues. These are leading to a reduction in floristic interest of the meadows and a reduction in suitability as breeding habitat for waders.
Limited water control structures throughout the Avon Valley make it difficult to regulate water levels of some key fields in spring. During the last 15 years there has been a large reduction in the number of livestock within the valley, with a shift from dairy herds to beef cattle. On many units within the SSSI the reason for unfavourable conservation status is under-grazing. Appropriate grazing management by farmers is essential to maintain the suitability of swards for breeding waders and wintering wildfowl. The ability to graze fields appropriately is closely allied to control over water levels so that livestock can gain access at certain times of year. These issues reduce the area of habitat suitable for nesting and ultimately reduce wader breeding success because birds are likely to be more vulnerable to predation and suffer lower availability of chick food in sub-optimal habitat.
A farmer-led approach to wader recovery
It is now clear that habitat quality and predation both have important influences on breeding wader populations, and population recovery is unlikely to be achieved without addressing both issues. Because adult survival remains high and birds are able to redistribute themselves in relation to habitat suitability, assessing the effectiveness of a wader recovery initiative should focus on breeding success, specifically the number of young fledged each year.
Integrated approaches involving both habitat and predator management are starting to be adopted on a few nature reserves, e.g. Elmley NNR (Kent) and Berney Marshes RSPB reserve (Norfolk). However, these sites consist of large, open landscapes with species-poor grassland reverted from arable land and are managed by single landowners with complete control over the grazing and other management of the site. At present we do not know whether it is feasible to implement the combination of habitat improvement and reduced predation in the wider countryside, such as more enclosed river floodplains with multiple small landholdings.
The Avon Valley is typical of river valley situations where other biodiversity considerations are also important and the feasibility of effectively reducing predator impacts is more constrained by the landscape and multiple land ownership. It therefore makes a good site for demonstrating what is achievable through a local, farmer-led initiative. Achieving wader recovery at non-reserve sites is likely to be logistically more difficult than on reserves, because it requires co-operation between landowners and some of the methods employed on reserves may need to be modified in order to be acceptable to farmers. We believe that given appropriate guidance on what is required by the birds, farmers are best placed to find effective systems of management and solutions to issues on their land, based on local knowledge and experience. Tailoring a range of predator exclusion and predator reduction measures to individual circumstances, based on an understanding of how different predators use the landscape, will be important.
In collaboration with Hampshire & Isle of Wight Wildlife Trust, and with EU Life+ funding, we plan to facilitate a farmer-led wader recovery programme during 2014-2018. The project will involve three main areas of innovation: the integration of processes for wader recovery in a non-reserve landscape, the creation of ‘hotspots’ as sources for re-colonisation and the tracking of predators to improve efficiency at reducing predation. Our project will inform the national debate about cost-effective management of sites for breeding waders by contributing information on the most appropriate techniques, problems encountered and the effort and costs involved.