Action Synopsis: Bird Conservation About Actions

Restore or create inland wetlands

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • Of eleven studies captured, 11, from the mainland USA, Guam, Canada and Hawaii, found that birds used artificially restored or created wetlands. Two found that rates of use and species richness were similar or higher than on natural wetlands. One found that use rates were higher than on unrestored wetlands.
  • Three studies from the USA and Puerto Rico found that restored wetlands held lower densities and fewer species of birds than natural wetlands.
  • A replicated study from the USA found that least bittern productivity was similar in restored and natural wetlands.
  • Two replicated studies examined wetland characteristics: one from the USA found that semi-permanent restored wetlands were used more than temporary or seasonal ones. A study from Hawaii found that larger restored wetlands were used more than smaller sites.


About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A study in 1958-1967 on Squaw Creek National Wildlife Refuge, Missouri, USA (Burgess 1969), found that annual use of the 2,772 ha wetlands (created in 1935)  varied from 6-27 million duck-days and from 7-19 million goose-days each year. Management included winter water removal to aerate the soil and eradicate carp, and spring flooding.

    Study and other actions tested
  2. A study in 1986 at the Savannah River Site, South Carolina, USA (Coulter et al. 1987), found that up to 94 wood storks Mycteria americana and over 210 other wading birds were seen on specially constructed and managed ponds at once. Ponds were created in a 14 ha depression and stocked with fish between 1985 and 1986.

    Study and other actions tested
  3. A before-and-after study in 1992 on Guam, South Pacific (Ritter & Sweet 1993), found that Mariana common moorhens Gallinula chloropus guami colonised a newly-created wetland within five months of its creation, with two adults and at least four chicks being seen. The wetland was 20-60 cm deep, 45 m long and up to 27 m wide and created using an excavator in January 1992. Spikerush Eleocharis dulcis, water lettuce Pistia stratiotesm, taro Colocasia esculenta and rusty flatsedge Cyperus odoratus were planted, although the taro died, probably because of excessive flooding.

    Study and other actions tested
  4. A replicated, controlled study in 1992-1994 in wetlands in the Lake Ontario and St. Lawrence River plains, New York State, USA (Brown & Smith 1998), found lower species richness and densities of wetland birds on restored wetlands compared with natural wetlands (6 species/ha and 15 birds/ha for 18 restored sites vs. 8 and 20 for eight natural sites). This pattern was stronger for wetland dependent species. Restored sites also had community compositions more similar to other restored sites than to natural wetlands. Birds were surveyed with an unlimited-radius point count within each wetland each year during the breeding season.

    Study and other actions tested
  5. A replicated study from April-June in 1985-1991 in a 13 ha wetland site in South Carolina, USA (Post 1998), found that least bitterns Ixobrychus exilis nested at high densities (12 pairs/ha), had a 50% hatching rate and 55% of nests produced fledglings. The author points out that this rate is only slightly lower than that reported for natural wetlands. An average of 2.7 fledglings/nest were produced from an average 3.8 eggs/clutch. Most egg mortality was caused by nest instability.

    Study and other actions tested
  6. A replicated, paired site study from May-July in 1997-1998 in 39 pairs of restored and natural wetlands in North and South Dakota, USA (Ratti et al. 2001) found that restored wetlands exhibited equal, and often greater, avian abundance, species richness and diversity. There were no significant differences in overall bird abundance, species richness or diversity; waterfowl breeding pair density or upland species richness between restored and natural wetlands. However, Canada goose Branta canadensis, mallard Anas platyrhynchos, redhead Aythya americana, and ruddy duck Oxyura jamaicensis exhibited significantly higher densities on restored wetlands. Total area bird counts were performed four times on each wetland.

    Study and other actions tested
  7. A replicated, controlled study from May-July in 2000 in Virginia, USA (Snell-Rood & Cristol 2003), found that bird species richness and diversity in artificially created wetlands were significantly lower than in natural wetlands (average of 11 species/site for six artificial wetlands vs. 17 for five natural wetlands). Although total bird abundance, and the abundance of wading birds, waterfowl, raptors, aerial feeders or woodpeckers were similar, natural wetlands had significantly higher songbird abundance. In addition, created wetlands exhibited bird communities with significantly lower conservation value (based trophic level and migratory status) but similar average habitat specificity and wetland dependency. All wetlands had similar surrounding habitats and were of similar ages (time since planting for created and since logging for natural wetlands), and sizes (5-15 ha).

    Study and other actions tested
  8. A replicated, controlled study in April 1998-1999 on Prince Edward Island, Canada (Stevens et al. 2003), found that six out of eight wildfowl species were found in significantly higher numbers in 22 restored wetlands than in 24 control (unrestored) wetlands. Four species also had significantly more broods at restored sites. Large wetlands, close to rivers and with a large proportion of cattails Typha spp. held more species than other sites. All sites were freshwater wetlands, 0.3-6.0 ha in size and restored sites were dredged, starting in 1990, to remove excess organic material.

    Study and other actions tested
  9. A small controlled study from 2004-2005 in Toa Baja, Puerto Rico (Acevedo 2007) found that fewer bird species were recorded in an 18 ha restored forested wetland than in a natural forested wetland (nine records of five species in restored site vs. 65 records of 16 species in the natural site). In addition, only one species (yellow-faced grassquit Tiaris olivaceus) was observed foraging in the restored wetland; 40% of records in the natural site were of foraging birds. Only two records, both of northern waterthrush Seiurus novaboracensis were made at a 14 ha control (unrestored) grassland site. The restored wetland was planted with 7,000 Pterocarpus officinalis and Annona glabra trees during 1997-2000.

    Study and other actions tested
  10. A replicated, randomised study in spring from 2004-5 in 28 small restored wetlands in Illinois, USA (O\'Neal et al. 2008), found that semi-permanent wetlands were used more frequently by waterbirds than temporary or seasonal wetlands and held more waterfowl broods (semi-permanent wetlands were used on 56% of days and held 1.1 broods/ha vs. 37% and 0.2 for seasonal and 7% and zero broods for temporary wetlands). Hydrologic management (passive restoration and management; active restoration through hydraulic engineering but passively managed or actively restored and managed through regulation of hydrologic regime) was the most important variable in explaining bird abundance and distributions. Of the 28 wetlands, 25 were <5 ha in size and 17 were <1 ha. Water birds included waterfowl, wading birds and shorebirds. Wetlands were classified as semi-permanent if there was surface-water throughout growing season; seasonal if there was surface water at the start, and for long periods of the growing season, but not by the end of it; and temporary if surface-water was only found for brief periods throughout the growing season.

    Study and other actions tested
  11. A replicated, site comparison study from March 2002 to July 2003 in wetlands in Kohala-Mauna Kea, Hawai’i (Uyehara et al. 2008) found that Hawaiian ducks Anas wyvilliana used 16 restored wetlands more often than 32 agricultural wetlands, despite the greater availability of the latter. Restored wetlands had a significantly higher occupancy rate than agricultural wetlands (81 vs. 41% of sampled sites) and higher consistency of occupancy (13 vs. 7% of all surveys). Hawaiian ducks preferred wetlands that were larger (>0.23 ha), further from houses and surrounded by more wetland habitat. No wetland within 600 m of a house was occupied. Wetland occupancy was not affected by presence of invasive species or grazing intensity. Wetlands ranged from 0.01-1.30 ha and were surveyed every two months.

    Study and other actions tested
Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2020) Bird Conservation. Pages 137-281 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.


Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Bird Conservation

This Action forms part of the Action Synopsis:

Bird Conservation
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 21

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape ProgrammeRed List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Mauritian Wildlife Supporting Conservation Leaders
Sustainability Dashboard National Biodiversity Network Frog Life The international journey of Conservation - Oryx Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered species Vincet Wildlife Trust