Action: Leave uncut strips of rye grass on silage fields
- Two reviews and two replicated controlled trials from the UK found that leaving uncut strips of rye grass on silage fields resulted in benefits to birds including increased numbers. One of these studies found that whilst seed-eating birds preferred rye grass cut once only, birds that fed on different food resources such as insect-eaters showed more variable results with some preferring plots cut two or more times.
- One replicated controlled randomized study from the UK found no difference in ground beetle abundance and diversity between cut and uncut silage field headlands in the first two years of the experiment, but higher species diversity in uncut plots in the third year.
This intervention involves leaving areas of uncut rye grass in silage fields. In the UK, seed-eating songbirds have declined across farmland, probably in part because of a lack of winter food. Rye grass Lolium perenne seeds are a potential food source, but cutting rye grass fields multiple times a year for silage removes seed heads before they can ripen and so reduces the food available to birds the following winter. Leaving fields or plots uncut may provide valuable overwinter food for birds and may also provide suitable habitat away from damaging harvesting machinery for other farmland wildlife such as invertebrates.
Supporting evidence from individual studies
A replicated, controlled, randomized study in 1996-1997 of a silage field headland in Scotland (Haysom et al. 1999) found that ground beetle (Carabidae) abundance and diversity did not differ significantly in cut and uncut headlands. Total abundance of ground beetles was highest in headlands cut three-times each year (105-201), followed by those cut annually (43-157), and those uncut (44-132). Specific species differed in their response to cutting regimes. In 1996, species diversity was highest in headlands cut three times each year (12), followed by those cut once (10) and uncut (9). In 1997, diversity in headlands cut once (14) was higher than uncut (11) and headlands cut three times (10) (results from 1997 are also presented in (Haysom et al. 2004)). Cutting regimes were assigned randomly within blocks to three 10 x 10 m plots. Cuts were in August and May, June and August. Cattle were excluded April-October and plots were intermittently grazed by sheep October-February. No pesticides were used and fertilizers were not used in the headland. Ground beetles were sampled using pitfall traps in late May-mid-July and late August-early October. Three pitfall traps parallel to the field edge were placed in the centre of each plot. Results from the third year of the experiment are presented in (Haysom et al. 2004).
A 2004 review of experiments on the effects of agri-environment measures on livestock farms in the UK (Buckingham et al. 2004) found that leaving perennial rye grass Lolium perenne silage uncut was shown to benefit seed-eating birds in winter in one experiment. No reference was given in the review for these results. The birds were only found in any numbers on plots left unmown, and were more abundant on plots left ungrazed than plots grazed from September. Yellowhammer Emberiza citrinella and reed bunting E. schoeniclus reached densities of 132 and 52 birds/ha respectively on unmown, ungrazed plots.
A continuation of the replicated, controlled, randomized study in Scotland in (Haysom et al. 1999), (Haysom et al. 2004) found that ground beetle (Carabidae) species diversity was significantly greater in the third year (1998) in uncut plots than those with one or three annual cuts. Species diversity was reported to be significantly higher in uncut plots (27 species) than cut plots (cut annually: 26 individuals, cut three times each year: 23) in 1998. It did not differ in 1997 (uncut: 20, cut: 26-27). The total abundance of ground beetles did not differ between treatments in 1997-1998 (uncut: 559-791 individuals, annual cut: 611-890 and cut three times: 927-1053). Specific species differed in their response to cutting regimes. Plots cut three times tended to have a similar species composition to the main field, whereas the uncut and annually cut plots tended to be more similar to the field boundary.
A replicated, controlled study of four silage fields on separate dairy farms in England (Buckingham & Peach 2006) found that numbers of yellowhammer Emberiza citrinella, reed bunting Emberiza schoeniclus, winter wren Troglodytes troglodytes, song thrush Turdus philomelos and Eurasian skylark Alauda arvensis were higher in plots left to set seed compared to mown plots, and in ungrazed seeded plots compared to grazed seeded plots. Significantly higher numbers of yellowhammer were observed in seeded plots (458 birds seen) compared to mown (one bird) and in ungrazed seeded plots (423) than grazed seeded plots (35). Reed bunting showed a similar response (seeded ungrazed: 160, grazed: 29; mown ungrazed: 3, grazed: 0). As did wren (seeded ungrazed: 22, grazed: 1; mown ungrazed: 2, grazed: 0) and song thrush (seeded ungrazed: 7, grazed: 3; mown ungrazed: 4, grazed: 0). There were more skylark in seeded than mown plots (18 vs 0), and more in grazed (17) than ungrazed seeded plots (1). Two of four plots (0.5 ha) in each field were left uncut when the third silage cut was taken in July-August 2002 so that the grass set seed. One mown and one seeded plot was grazed by cattle until October, cattle were excluded from the other two plots. Numbers and species of birds using each plot were recorded over eight 1 hour periods between November 2002 and February 2003.
A 2010 review of four experiments on the effects of agri-environment measures on livestock farms in the UK (Buckingham et al. 2010) found that leaving perennial rye grass Lolium perenne silage uncut was shown to benefit seed-eating birds in winter in one experiment. These are further results from a study discussed in (Buckingham et al. 2004), with no reference given (Defra project BD1455). Only plots cut once during the previous season produced large seed crops and attracted yellowhammer Emberiza citrinella (5.5 birds/visit on average) and reed bunting E. schoeniclus, (approximately 2 birds/visit on average) but not finches. Plots cut twice or three times (control) did not attract these birds. Birds were observed over two winters.
A replicated, controlled study on 12 farms in the West Midlands, UK (Defra 2011) in the winters of 2007-2009, found that seed-eating birds (yellowhammer Emberiza citrinella and reed bunting E. schoeniclus) preferentially foraged in perennial rye grass Lolium perenne fields that were only cut once for silage and ungrazed, compared to twice cut (ungrazed) or control (two or more cuts and grazed) plots. Meadow pipit Anthus pratensis (which eat seeds and insects) did not show a preference for perennial rye grass fields under different treatments and showed a weak preference for other rye grasses that were only cut once. Insect-eating winter wren Troglodytes troglodytes preferentially foraged in all treatments except controls. Insect-eating European robin Erithacus rubecula preferentially foraged on control plots.
- Haysom K.A., McCracken D.I., Foster G.N. & Sotherton N.W. (1999) Grass conservation headlands - adapting an arable technique for the grassland farmer. Aspects of Applied Biology, 54, 171-178
- Buckingham D.L., Atkinson P.W. & Rook A.J. (2004) Testing solutions in grass-dominated landscapes: a review of current research. Ibis, 146, 2-163
- Haysom K.A., McCracken D.I., Foster G.N. & Sotherton N.W. (2004) Developing grassland conservation headlands: response of carabid assemblage to different cutting regimes in a silage field edge. Agriculture, Ecosystems & Environment, 102, 263-277
- Buckingham D.L. & Peach W.J. (2006) Leaving final-cut grass silage in situ overwinter as a seed resource for declining farmland birds. Biodiversity and Conservation, 15, 3827-3845
- Buckingham D.L, Atkinson P.W., Peel S. & Peach W. (2010) New conservation measures for birds on grassland and livestock farms. Proceedings of the Lowland Farmland Birds III: delivering solutions in an uncertain world, 60.
- Defra (2011) Grass silage as a new source of winter food for declining farmland birds. RSPB report.