Action: Mow or cut natural grasslands
- Of six studies, two replicated and controlled studies from the USA found higher densities of birds or nests on mown grasslands, compared to unmanaged or burned areas. Two controlled studies from the USA, one replicated, found lower nesting or population densities of some species, on mown grasslands compared to unmown areas. Two replicated and controlled studies found no significant differences in nesting densities or community composition between mown and unmown areas.
- One study from the USA found that grasshopper sparrow nesting success was higher on mown areas than grazed areas of grassland. A replicated controlled study from the USA found that ducks had similar nesting success on cut and uncut areas.
Cutting and mowing of grasslands can help maintain grass cover, as grasses can survive cutting, whilst herbs and woody plants may not. Cutting can also encourage grass re-growth and increase productivity. Alternatively, in improved soils, cutting and removing the cut vegetation can reduce the nutrient content of the grassland and allow species that rely on nutrient poor soils to return.
Supporting evidence from individual studies
A replicated and controlled study in between five and eight meadows in the Lower Souris National Wildlife Refuge, North Dakota, USA, in 1961-1962 (Martz 1967), found that duck pair density (mainly blue-winged teal Anas discors and gadwall A. strepera) was 6% lower in three areas mown in August than in five control areas. This difference was not significant and gadwall mostly nested in unmanaged areas beside mowed meadows and blue-winged teal frequently nested in mowed meadows. Nest success did not differ significantly between mowed and unmown meadows. A total of 398 nests were surveyed.
A replicated and controlled study in 1990-1994 in two intensively managed grassland sanctuaries in southeast Illinois, USA (Herkert et al. 1999), found that short-eared owls Asio flammeus were more likely to nest on fields burned and mowed in the last 12 months than on controls (undisturbed for 12 months). Northern harriers Circus cyaneus hudsonius were less likely to. Mowing was conducted between 20th June and 15th July each year. This study is discussed in detail in ‘Use prescribed burning’.
A replicated, controlled trial in May-June 1995-1996 in grasslands in Prairie Ridge State Natural Area, Illinois, USA (Walk & Warner 2000), found that native grasslands mown between late July and October held higher average densities of five songbird species than unmanaged native and non-native grasslands and mowed, hayed and burned non-native grasslands. Mowed and hayed non-native grasslands held lower average densities than unmanaged or grazed grasslands but higher densities than burned non-native grasslands. However, species showed individual responses to different managements. The species surveyed were eastern meadowlark Sturnella magna, dickcissel Spiza americana, Henslow’s sparrow Ammodramus henslowii, field sparrow Spizella pusilla and grasshopper sparrow A. savannarum. This study is discussed further in ‘Use prescribed burning’ and ‘Graze grasslands’.
A replicated, randomised and controlled study in DeSoto National Wildlife Refuge, Iowa, USA (van Dyke et al. 2004), found that bird communities were not fundamentally different between areas of tallgrass prairies mown on a 3-4 year rotation and unmanaged or burned prairies (12 species/site for four mowed areas vs. 10 species/site for four burned and 11 species/site for four controls). This study is discussed in detail in ‘Use prescribed burning’.
At Blue Grass Army Depot, Kentucky, USA (Sutter & Ritchison 2005), a site comparison study in April-August 2002-2003 found that grasshopper sparrow nesting success was significantly higher in a 3,950 ha area mown in July-August compared to a 2,100 ha cattle-grazed area (70% of 34 nests in mown areas fledging at least one young vs. 25% of 12 in grazed; overall survival estimated at 46% vs. 9%). Average clutch size in the mown area (five eggs) was significantly larger than in grazed area (four eggs).
A controlled study in 1999-2001 on Nantucket Island, Massachusetts, USA (Zuckerberg & Vickery 2006), found that song sparrows Melospiza melodia were significantly less abundant on mown grasslands (between one and three cuts annually), compared to controls (1 bird/10 ha on mown grasslands vs. 6 birds/10 ha on controls). There was no significant difference between mown and burned grasslands. Savannah sparrows Passerculus sandwichensis were equally abundant (7-9 birds/10 ha) on all treatments.
- Martz G.F. (1967) Effects of nesting cover removal on breeding puddle ducks. The Journal of Wildlife Management, 31, 236-247
- Herkert J.R., Simpson S.A., Westemeier R.L., Esker T.L. & Walk J.W. (1999) Response of northern harriers and short-eared owls to grassland management in Illinois. The Journal of Wildlife Management, 63, 517-523
- Walk J.W. & Warner R.E. (2000) Grassland management for the conservation of songbirds in the Midwestern USA. Biological Conservation, 94, 165-172
- van Dyke F., van Kley S.E., Page C.E. & van Beek J.G. (2004) Restoration efforts for plant and bird communities in tallgrass prairies using prescribed burning and mowing. Restoration Ecology, 12, 575-585
- Sutter B. & Ritchison G. (2005) Effects of grazing on vegetation structure, prey availability, and reproductive success of grasshopper sparrows. Journal of Field Ornithology, 76, 345-351
- Zuckerberg B. & Vickery P.D. (2006) Effects of mowing and burning on shrubland and grassland birds on Nantucket Island, Massachusetts. Wilson Journal of Ornithology, 118, 353-363