Background information and definitions
Early-season, mechanised mowing is thought to be responsible for declines in the UK and elsewhere of species such as the corncrake Crex crex, with chicks killed and nests destroyed by mowing machinery. Delaying mowing until after chicks can escape is therefore a part of many agri-environment schemes.
Supporting evidence from individual studies
A 2000 literature review (Aebischer et al. 2000) found that the UK population of corncrakes Crex crex increased from 480 to 589 males between 1993 and 1998 (an average rise of 3.5%/year) following schemes to get farmers to delay mowing dates and to leave unmown ‘corridors’ to allow chicks to escape to field edges which are thought to increase chick survival.Study and other actions tested
Referenced paperAebischer N.J., Green R.E. & Evans A.D. (2000) From science to recovery: four case studies of how research has been translated into conservation action in the UK. Pages 140-150 in: J.A. Vickery, P.V. Grice, A.D. Evans & N.J. Aebischer (eds.) The Ecology and Conservation of Lowland Farmland Birds. British Ornithologists' Union, Tring.
A 2002 review (Green) states that the British population of corncrakes Crex crex increased by 34% between 1993 and 2001, following the implementation of the \"Corncrake Initiative\" which financially compensates farmers who agree to delay mowing until after chicks can escape machinery. A second programme, begun in 1999, also included the provision of suitable cover. Both were based in western Scotland, where the remaining British population was found.Study and other actions tested
A replicated and controlled paired sites study in the western Netherlands in 2003 (Verhulst et al.) found that 19 grassland plots with delayed mowing had significantly higher breeding densities of waders, compared to 19 paired, control plots (approximately 8 territories/plot for delayed-mowing plots vs. approximately 3 territories/plot for controls). This difference was not apparent when delayed mowing was combined with per-clutch payment, and there were no differences in abundances of waders or all bird species. However, when delayed mowing was combined with per-clutch payment, breeding densities of all bird species was significantly higher (13 territories/plot for combined schemes; 11 territories/plot for controls). There were higher numbers of redshank Tringa tetanus on combined plots (approximately 5 birds/plot for combined schemes; 5 birds/plot for per-clutch payment and 3 birds/plot for controls), but not on delayed-mowing plots. There were higher abundances of northern lapwing Vanellus vanellus on control plots, compared to delayed-mowing plots, but this difference was not significant (approximately 18 birds/plot for controls vs. 13 birds/plot for delayed-mowing plots). There were no significant differences in breeding densities for redshank, northern lapwing, Eurasian oystercatcher Haematopus ostralegus or black-tailed godwit Limosa limosa. The authors suggest that groundwater depth, soil hardness and prey density were drove these patterns. All farms had been operating the schemes for an average of four years before the study. This study is also discussed in ‘Offer per-clutch payment for farmland birds’.Study and other actions tested
A replicated, controlled, before-and-after study in 1,040 grassland areas in the Netherlands, between 1990 and 2002 (Breeuwer et al. 2009), found that nesting densities of black-tailed godwit Limosa limosa and redshank Tringa totanus were higher in areas with management agreements with postponed mowing, but these differences were present before the agreements came into effect. Population trends were similar between management and control areas for godwits and Eurasian oystercatchers Haematopus ostralegus, but northern lapwing Vanellus vanellus and redshank declined on management areas, relative to controls. Mowing was postponed on management areas to the end of May or beginning of June.Study and other actions tested
A replicated, controlled study in Arkensas, USA, in 2003 (Luscier & Thompson 2009) found that a far higher percentage of grassland bird nests were destroyed by haying operations in two early-cut fields (cut from 26-31 May), compared to four late-cut fields (cut 17-26 June) (88% of 17 nests destroyed in early-cut fields vs. 4% of 52 nests destroyed in late-cut fields). The two surviving nests in early-cut fields did not fledge any chicks. Following early cutting, only one nest was started in early cut fields (0.03 nests/ha) compared with 0.13 nests/ha in uncut fields (seven nests) and 0.13 nests/ha in late-cut fields (11 nests). Nests were of dickcissel Spiza americana (32 nests), red-winged blackbird Agelaius phoniceus (30 nests), field sparrow Spizella pusilla (14 nests) and eastern meadowlark Sturnella magna (13 nests) and nest densities were similar across field types before haying (0.3-0.5 nests/ha).Study and other actions tested