Breeding Waders of English Upland Farmland (BWEUF): Survey and Data Analysis for Breeding Waders on In-Bye Land
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Breeding Waders of English Upland Farmland (BWEUF): survey and data analysis for breeding waders on in-bye land Report to Natural England Gavin Siriwardena, Greg Conway (British Trust for Ornithology) Andrew Stanbury, Mark Eaton (Royal Society for the Protection of Birds) Summary 1. Building on the significant conservation concern for waders breeding in in-bye farmland in England, this project assessed the importance of in-bye land and the management thereof under agri-environment schemes (AESs) for these species, using a combination of analyses of existing data sets and a new survey of the relevant habitats in 2016. The focal species were Curlew Numenius arquata, Golden Plover Pluvialis apricaria, Lapwing Vanellus vanellus, Oystercatcher Haematopus ostralegus, Redshank Tringa totanus and Snipe Gallinago gallinago. 2. Throughout this project, an operational definition that ‘in-bye’ farmland consisted of all agricultural land below and within 1km of the ‘moorland line’ (latter as delimited by Natural England) was used. ‘In- bye tetrads’ (2×2km grid squares) are nominally those with greater than 20% cover of in-bye farmland. 3. The strongest historical analysis available made use of data from Bird Atlas 2007-11 (Balmer et al. 2013) and changes in distribution from the data collected under the previous atlas project (Gibbons et al. 1993). Analyses of the influence of AES management on the local colonization and local extinction of the target species in in-bye 2×2km tetrads throughout England were conducted. 4. Despite presence-absence analyses providing only coarse measures of population change, there were several significant relationships between AES management and the target species. Overall, Environmentally Sensitive Area (ESA) management tended to be associated with negative changes (local extinction or lack of colonization), whereas Environmental Stewardship (ES)/Countryside Stewardship Scheme (CSS1) management was associated with positive effects. The negative ESA effects in respect of colonization prevailed for all species except Redshank, while ES and CSS showed significantly positive associations for Curlew, Lapwing and Snipe. Local extinction was apparently promoted by ESAs for Curlew and Lapwing, but restricted by ES/CSS for Curlew. It is important to note that all these results are correlative and that the associations do not prove either positive or negative effects of the different AES schemes. 5. A wide range of other data sources that potentially inform about changes in in-bye wader populations were collated, totalling 105 datasets, but the disparate survey/recording methods used and limited recording of survey effort in space and/or time in some surveys limited their utility for investigating long-term trends and the effects of management upon them. These data covered many local areas and discrete time periods within the range from the early 1980s to the present. As a compromise among the range of data resolutions available, data were pooled at the 2×2km tetrad level. Where they were not explicitly recorded, zero records for species were inferred where possible; data providing presence information only were discarded. Analyses then proceeded using models of presence-absence by year at the tetrad scale: the disparate survey methods used made comparing counts unreliable. These considered both temporal trends and local colonization/extinction. 1 As distinct from the latest AES in England, which is similarly named ‘Countryside Stewardship (CS)’. 6. Final analyses used data from 1994 onwards and were dominated by BBS data because the quality of the other data sources for the present analysis was often low. The data were less standardized than Atlas data, but revealed some of the same patterns in respect of local colonization or extinction. These analyses therefore add little to the inference already gleaned from Atlas data. Analyses of the variation in linear trends in presence over time with respect to AES management also produced little evidence for important patterns not detected by the Atlas analyses. 7. Novel population trends based on these presence-absence analyses revealed long-term declines in Curlew, Lapwing and Redshank, but increases in Oystercatcher and a noisy pattern, but overall stability, for Snipe. These patterns are similar to those reported for these species for terrestrial habitats in England by the BBS. 8. A new survey of waders in in-bye farmland was designed, set up for online coordination and data inputting, and conducted during 2016. The survey unit was the tetrad and candidates for coverage were selected with respect to recorded counts of the target waders in Bird Atlas 2007-11, with the rule that at least 80ha of the tetrad had to be ‘in-bye farmland’. Tetrads were selected for survey randomly, within strata based on Atlas counts. Coverage was then split between professional surveyors employed by RSPB and volunteers, such that a total of 522 of the total of 2837 candidate tetrads identified in England were surveyed, with a bias towards areas with larger wader populations. Tetrads were visited twice in Spring 2016, with birds and habitat being recorded by field within the in-bye area and controls in place to avoid bias due to partial coverage. 9. Data were analysed to address: (i) the abundance and distribution of the target species in in-bye habitats and how these relate to recent estimates for the total populations in England; (ii) how the patterns of distribution and abundance of the target species relate to those of key current and historical AES options. For testing, AES options were grouped into non-exclusive categories describing broad forms of management and/or nominal effects on waders: grazing, restoration, nesting, feeding, nesting and feeding, and hay. Tests were also conducted using total areas of ESA and ES/CSS. 10. Significant numbers of breeding pairs of all the target species were found in in-bye fields, with the exception of Golden Plover, but the latter species was frequently recorded foraging in in-bye areas. An estimated 14% of English Redshanks and 28% of Oystercatchers are found in in-bye, reflecting their primarily coastal distributions, whereas in-bye supported 48-67% of Curlew, Lapwing and Snipe, showing the importance of the habitat for these declining species. Estimates of the total populations found in in-bye land for each species were as follows (median number of pairs and 5th-95th percentile range): Curlew 15039.5 (10551.5 - 20747.7), Golden Plover 173.5 (28.8 - 440.9), Lapwing 27243.4 (18143.6 - 37917.9), Oystercatcher 6828.1 (4043.9 - 10603.7), Redshank 1604.4 (628.1 - 3092.2) and Snipe 4527.5 (2064.1 - 8090.6). 11. In analyses of associations between waders and AES management at the tetrad scale, there were significant, positive results for all of the target wader species, except Golden Plover. The patterns were especially strong for Curlew and for options for grazing and restoration, among the management types considered. The only negative association found was for Curlew and ESA management, which could show a failure of management or independent associations between particular regions and each of ESA management and wader abundance. The positive associations found suggest that AES management in the grazing, restoration and, to a lesser extent, feeding categories could be widely beneficial across species, but it should be noted that these associations are strictly correlative and do not necessarily imply that AES management has driven the variation in abundance. In particular, such patterns could arise through the targeting of AES towards existing areas of high wader density. 12. Analyses of associations between waders and AES management within tetrads show positive associations for all species except Golden Plover, reflecting the limited use of in-bye habitat only for foraging by this species. Curlew adult counts showed a significant negative association with ESA management. There were no significant associations for breeding pairs with hay. Management directed at restoration/maintenance and provision of feeding and nesting habitat generally has significant positive associations for all species except Golden Plover, both for breeding pairs and total adult counts. 13. Analyses of associations between waders and the key features of in-bye field habitats mostly reflect well-established patterns in wader ecology, such as the avoidance field boundaries, preference for heterogeneous vegetation and reliance on wet ground. Variation in preferences for specific field types across species and between measures of feeding versus nesting birds reveal a diversity in species’ ecologies that underlines the importance of habitat heterogeneity at the field or landscape scale to support the entire wader community. 14. This study has confirmed that in-bye farmland is important for several wader species, with consistent results from long-term changes in distribution and fine-scale distribution in 2016, both at the tetrad scale and within tetrads, although populations continue to fall. There is evidence that conservation action via ES/CSS may be having positive effects, but ESAs are associated with negative effects. The causality of these correlative patterns with AES management remains uncertain. It would be valuable to repeat the survey conducted in this study in around five years to investigate the influence of management on population changes and to allow more confident inference about the causality of the changes observed. Introduction A number of breeding waders have