Action: Restore or create coastal and intertidal wetlands
- All six studies found, from the USA and UK, found that target bird species used restored or created wetlands. Two found that numbers and/or diversity were at least as high as in natural wetlands, one that numbers were higher than in unrestored sites. Three found that bird numbers on wetlands increased over time.
- Two studies from the UK found that songbirds and waders decreased following wetland restoration, whilst a study from the USA found that songbirds were more common on unrestored sites than restored wetlands.
Coastal and intertidal wetlands are those that can be inundated with salt water. This can have profound consequences for the vegetation and animal life, as salt-intolerant species are excluded.
This form of habitat creation may form part of coastal protection measures, with habitats such as saltmarshes and mangroves being important in reducing the power of waves and so reducing coastal erosion.
Supporting evidence from individual studies
A controlled study in 1972-1976 on two former and one current ‘salt hay’ farms in Delaware Bay, New Jersey, USA (Slavin & Shisler 1983), found that there were significantly more species of waders, waterfowl and gulls on the former farms that were inundated by seawater following breaching of the dykes surrounding the farm. Significantly more songbird species were found on the current farm. After the dykes were breached, the plant community changed dramatically, with a 98% increase in salt marsh plants, an 88% decrease in salt hay species and a 97% increase in surface water.
A controlled study in summer 1993-1994 in Spartina-dominated marsh at Barn Island Wildlife Management Area in Connecticut, USA (Brawley et al. 1998), found that wetland birds quickly recolonised tidally-restored marsh, with a 21 ha marsh reopened to tidal exchange in 1982 holding a greater species richness and abundance of birds than three ‘reference’ marshes (1.2, 8 and 19 ha) and a 12 ha marsh under restoration since around 1984.
A before-and-after study at two sites in Essex, UK (Atkinson et al. 2004), found that the number of waders using the sites increased in the first two winters after the surrounding seawall was breached in August 1995. At one site (Tollesbury, 20 ha) the number of waders stabilised after increases in the first two winters, particularly in common redshank Tringa totanus and dunlin Calidris alpine; whilst the number of songbirds decreased after the first winter. Some species (e.g. knot Calidris canutus) did not start using the site until the third winter. At the second site (Orplands, 42 ha), the number of common redshank, dunlin and grey plover Pluvialis squatarola increased during the first winter and then the community composition changed across the site, with higher areas holding similar species to adjacent saltmarsh and lower areas being similar to mudflats.
A before-and-after study at Freiston Shore, Lincolnshire, England (Bradley & Allcorn 2006), found that the number of wildfowl and little egrets Egretta garzetta using the site increased from 426 and one, respectively to 2,659 and 14 between 2002-2003 and 2005-2006. This followed the breaching of the sea wall at the site, allowing the flooding of 66 ha of land in 2002. By September 2005, 70% of the area was covered in salt marsh plants. However, the number of waders at the site decreased from 11,012 to 7,799 over the same period, and the authors note that the regular inundation with salt water prevents waders from breeding. Songbirds showed mixed responses: Eurasian skylarks Alauda arvensis increased from an average of 16 birds to 121; four species increased by smaller amounts; three species showed uncertain trends; meadow pipits Anthus pratensis declined.
A replicated, paired study in January-March 2002 in southern California, USA (Armitage et al. 2007), found that wader diversity was higher in three out of five restored wetlands compared to on paired control (non-degraded) sites, lower on one and similar on a fifth. In addition, total density was as high or higher in four restored sites (although responses varied between species) and behaviour was similar across restored and controlled sites, with over 85% of three of the four species groups observed feeding. Densities of willets Catoptrophorus semipalmatus were often higher in restored sites whereas densities of marbled godwits Limosa fedoa were often denser in control sites. The authors conclude that wetland restoration should be considered at a landscape scale because each site is beneficial for a different assemblage of species.
A before-and-after study of a large-scale wetland restoration project in Chesapeake Bay, Maryland, USA (Erwin et al. 2007), found that five out six ‘priority species’ colonised the site before 2005 after restoration began in 2002 (although the project was started in 1998). Snowy egret Egretta thula, cattle egret Bubulcus ibis, osprey Pandion haliaetus, common tern Sterna hirundo, and least tern S. antillarum all bred, with over 800 pairs of common terns. American black duck Anas rubripes, however, had not colonised the site by 2005. The authors note that tern reproductive success was very low, largely because of predation.
- Slavin P. & Shisler J.K. (1983) Avian utilisation of a tidally restored salt hay farm. Biological Conservation, 26, 271-285
- Brawley A.H., Warren R.S. & Askins R.A. (1998) Bird use of restoration and reference marshes within the Barn Island Wildlife Management Area, Atonington, Connecticut, USA. Environmental Management, 22, 625-633
- Atkinson P.W., Crooks S., Drewitt A., Grant A., Rehfisch M.M., Sharpe J. & Tyas C.J. (2004) Managed realignment in the UK - the first 5 years of colonization by birds. Ibis, 101-110
- Badley R. & Allcorn R.I. (2006) Changes in bird use following the managed realignment at Freiston Shore RSPB Reserve, Lincolnshire, England. Conservation Evidence, 3, 102-105
- Armitage A.R., Jensen S.M., Yoon J.E. & Ambrose R.F. (2007) Wintering shorebird assemblages and behavior in restored tidal wetlands in southern California. Restoration Ecology, 15, 139-148
- Erwin R.M., Miller J. & Reese J.G. (2007) Poplar island environmental restoration project: Challenges in waterbird restoration on an island in Chesapeake Bay. Ecological Restoration, 25, 256-262