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Research into action: grey partridge conservation as a case study

2013; Wiley; Volume: 51; Issue: 1 Linguagem: Inglês

10.1111/1365-2664.12162

1365-2664

N. W. Sotherton, Nicholas J. Aebischer, Julie A. Ewald,

Fish Ecology and Management Studies

The grey partridge Perdix perdix L. has been described as one of the archetypal farmland birds. Like the skylark Alauda arvensis and the corn bunting Emberiza calandra L., it is closely associated with open-farmed landscapes (Potts 1986) and is therefore sensitive to changes in farming intensity. It has undergone a 91% decline in abundance between 1970 and 2009 (Eaton et al. 2010) and a 19% contraction in range between 1970 and 1990 (Gibbons, Reid & Chapman 1993). As a result of these declines, the grey partridge is on the UK red list of Birds of Conservation Concern (Eaton et al. 2009) and was designated as a Biodiversity Action Plan species (Anon 1995). It is also one of the nineteen species that make up the Farmland Bird Index and one of the UK's official Biodiversity 2020 indicators (DETR 1999). Historically, grey partridge numbers fluctuated according to the economic viability of British agriculture, doing badly during periods of agricultural slump (pre-repeal of the Corn Laws in 1832, the 1930s depression) and doing well during the years of arable expansion (Napoleonic Wars) (Potts 1986). The current sustained decline in grey partridge numbers began in the 1950s as evidenced from national bag data and March pair counts (Potts 1986). This was the time when the UK's agricultural industry began the process of intensification, both increasing production per unit area and polarizing production so that mixed arable/livestock farms were replaced in the west by all-grass farms and in the east by all-arable farms (Donald, Green & Heath 2001). Agricultural policy still has an important influence on grey partridge distribution and abundance as elements of wildlife conservation are introduced to National and European policies in the form of agri-environment schemes and as the take-up of such schemes is affected by the international price of commodity crops such as cereals (e.g. Pain & Pienkowski 1997). By 1967, the extent of the decline was sufficient cause for concern that the Game & Wildlife Conservation Trust (GWCT) and its predecessors embarked upon a programme of applied research to understand the causes of the decline, starting with the Sussex Study (Potts 1980). Long-term monitoring and hypothesis-driven, large-scale experiments have been vital in unravelling the causes of this decline and have been followed up by applied research developing practical solutions to stimulate population recovery. Other declining farmland bird species have since also been extensively studied (e.g. Green et al. 1997; Tyler, Green & Casey 1998; Green, Tyler & Bowden 2000; Peach et al. 2001), but the grey partridge remains the only species where such an extensive experimental approach has been adopted to discover the causes of decline and the road to recovery (Aebischer & Ewald 2012). The GWCT's Sussex Study began in 1968 across 62 km2 of the Sussex Downs between the rivers Arun and Adur. As the importance of invertebrates in the diet of young partridges became obvious, the project was expanded in 1970 to include the monitoring of cereal invertebrates and arable flora upon which these invertebrates relied. The analysis of the relationship between grey partridge population parameters, invertebrate resources, nesting cover and predator management resulted in the production of a grey partridge population simulation model and the calculation of a grey partridge chick-food index (CFI) (Potts 1980; Potts & Aebischer 1991). This model underpins the GWCT's subsequent grey partridge research and its advice to landowners on how to restore grey partridge numbers. Key factor analysis, applied to the Sussex Study data, identified poor levels of chick survival as the specific source of mortality responsible for population decline (Potts 1986). Southwood & Cross (2002) experimentally demonstrated the importance of an insect-rich (proteinaceous) diet to the growth and development of grey partridge chicks in the first 2 weeks after hatching. Potts and Aebischer (1991) showed a significant positive relationship between chick survival and the abundance of chick-food insects in cereal crops in the third week of June, the peak chick hatching time. The experimental exclusion of herbicides and insecticides from the edges of cereal crops to protect chick-food insects demonstrated that threefold increases in insect abundance could be achieved compared with areas that were sprayed according to common farm practice (Sotherton 1991). From this work came the concept of the selective exclusion of pesticides to protect insect resources at the field margins while allowing profitable farming to continue. Increases in plant density and species richness, abundance of chick-food insects and grey partridge chick survival have all been recorded (Sotherton 1991). These 'Conservation Headlands' were some of the first mitigation practices made available to conservation-minded farmers in the UK who established them on a voluntary basis to protect wildlife (Rands 1985; Sotherton 1991). Conservation headlands went on to become one of the earliest cereal-based options in the first UK agri-environment schemes (AES), that is, Countryside Stewardship and Environmentally Sensitive Areas. Predation during nesting and incubation was also found to be important in determining grey partridge densities. Data from the Sussex Study suggested that this predation could be density-dependent where there was no predator control, indicating a possible large effect on grey partridge numbers (Potts 1986). Predictions from a grey partridge population simulation model suggested that equilibrium densities of grey partridge could be up to four times higher 8 years after instigating a predator removal programme. To test this model prediction, during the 1980s a predator exclusion experiment was set up on Salisbury Plain in southern England. For 3 years, a gamekeeper attempted to remove predators that could be legally taken on a 564-ha area of farmland. We compared grey partridge breeding success and density with an equivalent area of farmland where no predators were removed. After 3 years, the keeper moved to the previously unkeepered area and his original beat reverted to the unkeepered control. The experiment then continued for another 3 years. Predator removal increased autumn density of partridges by 75% each year and led to a 3·5-fold difference in autumn density between keepered and unkeepered areas after 3 years. Predator removal also increased breeding pair densities by 35% each year and produced a 2·6-fold difference between keepered and unkeepered areas over 3 years. On the unkeepered plots, over each three-year period, autumn densities fell by 37%. During periods of predator removal, densities increased by 56% (Tapper, Potts & Brockless 1996). Predator removal was seasonal, only operated during the nesting season and strictly within the legal requirements of what species could be taken and how. Increasingly, the impact of such predator control on ground-nesting birds is becoming apparent for species other than the gamebirds. Fletcher et al. 2010 found a significant improvement in breeding success and spring density of waders (but not passerines) following predator removal on moorland. The third essential element in grey partridge conservation ecology is the provision of sufficient nesting cover of adequate quality. Monitoring in Sussex showed how the increase in field size and the resulting loss of nesting cover during the mid-1970s affected grey partridge breeding density (Potts 1986). In surveys of nesting cover, Rands (1986) recognized the importance of non-cropped cover, usually at the edges of fields along the grassy strips bounding hedgerows and other field margins. Specifically, the presence of a grassy strip containing abundant dead grass and the presence of a grassy bank providing a more freely draining site were identified as desirable elements of nesting cover. From this work came the concept of providing grassy field margins, containing abundant tussocky perennial grasses and the idea of recreating such cover as strips across the increasingly large fields associated with intensively farmed agricultural land ('Beetle Banks', Thomas, Wratten & Sotherton 1992). Originally designed to harbour high densities of polyphagous predatory invertebrates to provide integrated pest management options in cereal crops, Beetle Banks provide excellent nesting cover for a range of species, including grey partridge (Thomas, Goulson & Holland 2001). Thus, in separate experiments and studies, the importance of the three main elements of grey partridge conservation (nesting cover, chick-food provision and predator control) was evaluated. From this work, management options for implementation on farmland were developed and put into place on an area of farmland to demonstrate the complete package. The demonstration area covered 996 ha comprising six farm holdings on light chalky land near Royston, Hertfordshire, in eastern England. An adjacent area of 1311 ha (seven holdings) constituted a reference area for comparison. From January 2002, the GWCT undertook the following measures to increase wild grey partridge densities on the Royston study area. The grey partridge simulation model was reshaped to take landscape characteristics into account, and this was used to predict a density of 18·6 pairs per km2 in spring on the demonstration area if all three elements of partridge management were adopted. By spring 2007, on the area where the researched habitat management prescriptions, feeding and predator control had been put in place, the densities had increased from 2·9 to 18·4 pairs per km2, effectively meeting the predicted target density, while on the reference area densities had gone from 1·3 to 4·2 pairs per km2. On these farms in Hertfordshire, the local Biodiversity Action Plan targets for grey partridge were achieved and exceeded within 5 years, almost exactly the time frame and density predicted by the grey partridge models developed from the Sussex monitoring work (Potts 1986; Potts & Aebischer 1991). In the private sector, individual estates that implement the management package for grey partridges are achieving considerable success and we regularly hear of new recovery projects across the UK and Europe. In Sussex, where the GWCT has been monitoring grey partridge numbers annually for over 40 years, one estate, where grey partridge numbers fell to only 11 birds on 1052 ha, implemented the recovery package used at Royston and in spring 2010 counted 20·1 pairs per km2 (Ewald, Potts & Aebischer 2012). In Ireland, where populations fell across the entire island of Ireland to only 24 birds, over 900 were counted in spring 2011 on a study site in County Offaly where again the full management prescription for recovery was implemented (Buckley et al. 2012). These successes with grey partridge have come on the back of resource provisioning through habitat creation and selective seasonal predator control during the nesting season. Whilst almost every UK conservation organization would support habitat management and creation, a number are uncomfortable with fox, mustelid and crow control despite evidence of the improvements to productivity that this can bring. As applied scientists, we still need to do more to quantify predation impacts, particularly to determine which predators have the strongest impact on prey species. For example, the role of mustelid predation has been questioned in the dynamics of the loss of lapwing nests (Bodey et al. 2011), and the relative importance of fox versus corvid removal should also be examined. Despite the growing body of evidence indicating the causes of the grey partridge decline and the indications that recovery was possible, the plight of grey partridges and other farmland birds was not considered for many years. Causes of grey partridge decline were considered as far back as the early 1970s when GWCT scientists suggested that herbicide use was removing the host plants of insects that are vital in the diet of newly hatched chicks (Potts 1980). Already the GWCT data sets were clearly showing the extent of the decline, but these data were not considered by government, regulators or the conservation community until much later. It was not until the mid-1990s, when the second Breeding Bird Atlas was published (Gibbons, Reid & Chapman 1993) and the BTO's Common Bird Census data were examined that the perilous plight of our farmland birds was identified, not just for grey partridges, but for other common widespread species such as lapwing Vanellus vanellus, tree sparrow Passer montanus, turtle dove Streptopelia turtur, skylark and linnet Carduelis cannabina. Perhaps concerns for farmland ecology could have been addressed a decade or more earlier than was the case? When this point has been raised we have been told that it was because we had data only on one species, implying more species declines were needed before action could be taken, and even that the status of the grey partridge as a quarry species disqualified it from conservation interest. However, by the mid-1990s, the decline of many other groups of farmland wildlife had been identified and was of equal concern (Sotherton & Self 2000). At this point, scientists began to use research findings to help design the agri-environment schemes that were becoming available to finance mitigation measures to halt wildlife declines. We measure the impact of our research work into policy by the uptake of our research-based management options in the AESs currently available in the UK. In England, of the 36 options available, six were entirely developed by the GWCT and in a further 23, our research played a major role in their scientific evaluation. Both conservation headlands and beetle banks form a major part of the 'Farmland Bird Package' for arable farmers (Winspear et al. 2010). Another function of applied scientists within the GWCT has been to get information about farmland wildlife recovery out and used by the farming community. The existence of science-based management prescriptions for recovery does not mean that farmers will embrace the opportunity or implement the correct suite of management options. Some view the AES's ability to deliver farmland wildlife recovery as poor or only moderately successful (Whittingham 2011). Uptake of the schemes in England has been high, but there has been an almost total lack of advice to accompany the schemes. As a result, many farmers have opted for the easy management options such as grassy strips at the edges of fields rather than ones addressing the more critical requirements of wildlife, such as insect-rich summer canopies (Hodge & Reader 2010). More targeted and refined planning needs to be in place before the next evolution of AES comes into being associated with the next round of CAP reforms in 2013. The GWCT has detailed the management options for grey partridge recovery and explained how to deploy AES and other measures to achieve this via downloadable factsheets on the Internet (http://www.gwct.org.uk/partridge). The GWCT also runs its Partridge Count Scheme (PCS), which began in 1933 and relies on farmers to count their own wildlife. Originally, it was a means of monitoring annual densities and breeding success through a network of around 90 gamekeeper participants who counted the birds on their land in spring and autumn. After the government nominated the GWCT as lead partner for the Grey Partridge Species Action Plan in 1996, the GWCT re-launched the PCS in 1998 under the banner 'Every one counts'. The re-launch sought to increase the national coverage and, in addition to the monitoring role, to use the contact with gamekeepers, farmers and landowners to encourage more and better management. Core to the approach was persuading such people that, even if they had only a few grey partridges on their land, it was worth making the effort to conserve them because every increase contributed to the restoration of the species. To help contributors count and monitor their own partridges, the GWCT produced a guide to ageing and sexing grey partridges in the spring and autumn. In addition, each contributor receives a spring and autumn newsletter, a minimum number of pairs to aim for and their own personalized Species Action Plan target and feedback on how to achieve this. Roughly 800 participants return spring and autumn counts each year. The farmers contributing to the Partridge Count Scheme are more likely to implement the AES options of most use to grey partridges and other farmland birds, particularly Conservation Headlands and Beetle Banks (Ewald et al. 2010). Bringing together people who are interested in grey partridges promotes enthusiasm and opportunities for information dissemination. In counties (or clusters of counties) with over 30 PCS contributors, the GWCT organizes local Partridge Groups with two meetings a year open to all contributors within the area. These meetings allow presentation and discussion of the latest research, management ideas and government agri-environment regulations relevant to grey partridges; they include field visits showing good management practice. PCS members feed information back to GWCT researchers on the practical aspects of implementing and managing agri-environment measures: knowledge exchange at its best is a two-way street. There are currently 14 Partridge Groups in the UK. From a practitioner's perspective, it is no longer enough just to conduct the science to solve the problems of declining wildlife. Policy and education steps need to be taken. Within the research charity sector, such things are more easily achieved, but in the University sector, it would be more difficult to see how such non-scientific outputs could be justified and how it might have contributed to one's Research Assessment Exercise (RAE). Others have already commented in the pages of Practitioner's Perspectives on the demise of applied research and the pursuit of the high impact factor (Gibbons, Wilson & Green 2011). We can only heartily agree. The research charity sector can also provide the long-term vision required to support the programme of research illustrated here. Long-term monitoring (over 40 years) and seven- to eight-year switchover experiments, and demonstration areas do not fit into the three-year time frames of PhD studies or Research Council grants. The introduction of the Research Excellence Framework (REF) to replace the RAE, with a new emphasis on research impact may improve the translation of applied research into practice. Successful restorations have been achieved for several species of farmland bird such as cirl bunting Emberiza cirlus, corncrake Crex crex and stone curlew Burhinus oedicnemus (Tyler, Green & Casey 1998; Green, Tyler & Bowden 2000; Peach et al. 2001). The relict populations of these species were mostly highly localized, and conservation efforts could be targeted more easily: fewer farmers need to be engaged, advice can be concentrated, and monitoring outcomes can be more easily achieved than for widespread and dispersed species such as the grey partridge and skylark. The declines in farmland wildlife can be reversed and the work on grey partridge clearly demonstrates this. Grey partridge spring densities on PCS properties have increased by 81% between 2000 and 2010, while the national population monitored by the BTO on its BBS plots has declined by 40% over the same period (Aebischer & Ewald 2012). This gives us hope because it seems that where farmers get the message and begin management they succeed. Clearly, not enough farmers are doing this to reverse the national trends, as monitored by the BTO. Such improvements have come about recently largely because of the funding made available for habitat creation via AES in the UK. These AES prescriptions have been for arable land, and farms that have successfully increased their grey partridge numbers have done so predominantly on such land. We have yet to see successful restoration projects on farms in the west of the UK, where intensive grassland management prevails. Severe decreases in abundance and loss of range have occurred in Wales and south-west England. Grey partridges have declined across Europe, but restoration projects are underway in Ireland, Sweden, Finland, Hungary and Belgium, often inspired by GWCT research and demonstrations. However, the future of such schemes and the security of their funding are not certain. What is certain is that applied research must continue, including research funded through private interest. This influence is particularly relevant to conservation management at a time when applied research is not properly or adequately supported in the public sector in the UK. Nick Sotherton studied Agricultural Zoology at the University of Newcastle-upon-Tyne and is very proud of his applied roots. He obtained his PhD in Agricultural Entomology at Southampton University. Julie Ewald received her PhD from the University of Glasgow. Her farming education, however, was completed in north-east Nebraska, USA, under the tutelage of her father. Nicholas Aebischer undertook his PhD at Durham University and is one of those rare individuals that can turn complicated mathematical equations into practical advice.