Action: Plough habitats
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- One of four studies (of two experiments), from the USA, found that bird densities were higher on ploughed wetland areas, compared to unploughed areas.
- Three studies of a site comparison study from the UK found that few whimbrels nested on ploughed and re-seeded areas of heathland, but these areas were used for foraging in early spring. There were no differences in chick survival between birds that used ploughed and re-seeded heathland and those that did not.
Ploughing can be used to reduce the dominance of some species, such as Spartina spp. on wetlands, or heathers, on heathland.
Supporting evidence from individual studies
A site comparison study in the Shetland Islands, Scotland (Grant 1992) found that areas of heath seeded with grass to improve them for livestock grazing were mostly avoided by nesting whimbrels Numenius phaeopus in favour of unimproved heathland. In 1986 and 1987, this study monitored whimbrels in five areas of heathland that had been partly seeded, four on the island of Fetlar, one on Unst. Of 111 nests, 89% were found in unseeded heathland. Most nests were on hummocks and amongst heather Calluna vulgaris. Seeding with grass after ploughing or harrowing resulted in the loss of hummocks and most heather, and created a predominantly grassy habitat. Surface-seeding, without ploughing or harrowing, created less marked changes, with hummocks and heather retained, although hummock height was lowered, and in some areas only dead or dying heather was present.
In a study using the same Shetland Island heaths as Grant (1992), Grant et al. (1992) found no significant difference in chick survival between chicks that used areas of heathland re-seeded with grass and those that did not. Individually marked chicks were monitored after hatching in 20, 23, and 26 broods in 1986, 1987 and 1988 respectively. In each year 35-65% of all chicks remained on heathland, while others (usually broods over 12 days old, from nests within 200 m of the alternative habitat) moved into other habitats.
At the same study sites as Grant (1992), Grant et al. (1992) found that areas of heath seeded with grass after ploughing or harrowing, and older pastures, were the main early spring feeding areas for at least 90% of whimbrel pairs in the study. Habitat use by individually marked whimbrels was monitored during the pre-laying period in spring 1987 and 1988, on five Shetland Island heathlands. The birds made little use of unimproved heathland (where most nest) or heathland areas seeded without ploughing/harrowing. The greatest quantities of prey species (earthworms, oligochaetes, and crane-fly larvae, tipulids) were found in the soil of ploughed or harrowed seeded areas of heath and older pastures, with more recently seeded areas holding the highest masses of crane-fly larvae.
A controlled study in 2003-2004 on mudflats and areas of Spartina alterniflora meadows in Willapa National Wildlife Refuge, Washington, USA (Patten & O'Casey 2007), found that average densities of waders and wildfowl were significantly higher on areas of Spartina meadow that were ploughed, compared to untreated areas or areas completely sprayed with herbicide (see ‘Treat wetlands with herbicide’). Densities of some groups were 100 times those on the control areas, whilst some species found on the tilled meadows were never found on untreated Spartina. In addition, densities of unidentified Calidris spp. sandpipers, dowitchers Limnodromus spp. and waterfowl were significantly higher on tilled areas than on bare mud. The area was ploughed in winter-spring 2001, disked in winter 2002, and spot-treated with glyphosate during the summers of 2003 and 2004.
- Grant M.C. (1992) The effects of re-seeding heathland on breeding whimbrel Numenius phaeopus in Shetland. I. Nest distributions. Journal of Applied Ecology, 29, 501-508
- Grant M.C., Chambers R.E. & Evans P.R. (1992) The effects of re-seeding heathland on breeding whimbrel Numenius phaeopus in Shetland. III. Habitat use by broods. Journal of Applied Ecology, 29, 516-523
- Grant M.C., Chambers R.E. & Evans P.R. (1992) The effects of re-seeding heathland on breeding whimbrel Numenius phaeopus in Shetland. II. Habitat use by adults during the pre-laying period. Journal of Applied Ecology, 29, 509-515
- Patten K. & O'Casey C. (2007) Use of Willapa Bay, Washington, by shorebirds and waterfowl after Spartina control efforts. Journal of Field Ornithology, 78, 395-400