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Rice (Oryza sativa) is one of the world's most important crops. The crop is grown in at least 114 countries, occupies over 156 million ha of land annually, is a primary source of nutrition for over half the world's human population and constitutes over a fifth of the global grain supply. Rice is generally grown under flooded conditions and, if managed appropriately, can provide important habitat for wetland species. Waterfowl, wading birds, shorebirds and other waterbirds use rice fields, foraging on a variety of prey, nesting in the crop and in fringing vegetation, and staging during migration. Conflicts also exist, with some cropping practices harmful to birds and some bird activity detrimental to yield production. Much early research on waterbirds in rice fields was conducted in Mediterranean Europe with only scattered work elsewhere. More recently, there has been a growing focus on the conservation value of rice fields, with studies from most of the major regions where rice is grown. The body of research has included: community studies of the range of birds that use rice fields, detailed studies of endangered species, behavioral studies of reproductive success, foraging ecology and movement, and applied studies of cropping techniques. As the world's natural wetlands diminish, researchers studying waterbirds in rice fields are working to globalize interactions with each other. Also, some researchers are working closely with conservation groups and rice growers to identify ways to maximize the benefits of agricultural wetlands while minimizing the agronomic costs.
Rice (Oryza sativa) is the main cereal grown in the Republic of Korea and Japan and is planted on 54% and 36% of agricultural lands, respectively. Information on the status of birds that use rice fields in these nations was reviewed. More than 30%, or 135 species of 430 native avian species, excluding 152 accidental visitors, use rice fields. The fields serve primarily as foraging habitat, providing aquatic prey for passage, summer and resident species and residual grains for winter visitors. Some species, such as the Grey-faced Buzzard (Butastur indicus), require a mosaic of rice fields and forests for successful breeding. However, most waterbirds prefer rice fields in wide, open plains rather than narrow rice fields surrounded by forest. At least 32 (24%) of 135 species that use rice fields are designated threatened at the global or national scale, and eleven (22%) of 49 globally threatened species found in Korea and Japan use rice fields. Populations of most granivorous and piscivorous waterbirds such as geese, cranes and herons tend to be stable or increasing. The Baikal Teal (Anas formosa) is an exception. The breeding ranges or populations of some carnivorous and insectivorous birds, such as the Ruddy-breasted Crake (Porzana fusca), Greater Painted Snipe (Rostratula benghalensis) and many shorebirds have shrunk in recent decades. Some agricultural and conservation sectors have succeeded in attracting many waterbirds by flooding fallow fields in the rice-growing season and post-harvest rice fields. Further research on the direct and indirect effects of agricultural practices and conservation measures is needed in Korea and Japan.
Data on wild birds in rice fields in China are scarce. The potential significance of Chinese rice fields, which represent about 6% of the world's wetland area, is considerable but whether this potential is met is largely unknown. In this review, traditional and modern Chinese rice agriculture are compared, including detailing historical changes and their implications for wild birds. Traditional practices, with one crop each year and long periods of fallow flooding, provide greater benefit to biodiversity and species such as the Crested Ibis (Nipponia nippon). The method and alternatives, such as rice-fish, duck-rice and swidden agriculture, are contrasted with modern techniques which, through associated water regimes and chemical use, have been implicated in the decline of biodiversity and of species such as the Black-faced Spoonbill (Platalea minor). Agrochemical use is particularly pertinent because China is likely to have been the world's largest pesticide consumer since the mid-1990s, with use greatest in rice (Oryza sativa). However, few studies have measured the direct effects of agro-chemicals on wild birds in China. The most detailed information on birds in China's rice fields comes from charismatic species such as the Crested Ibis and Red-crowned Crane (Grus japonensis). Preliminary data from possibly the first systematic bird survey of a Chinese rural county are presented. More detailed and widespread studies of the implications of rice agriculture to wild birds in China are required.
The Indian subcontinent has the world's highest cropland cover per unit area with rice (Oryza sativa) being the second-most important crop, and is home to nearly 1,300 species of birds. The significance of rice fields as bird habitat in the region is not well understood and the subject is reviewed using a combination of published and secondary information. Rice fields in the subcontinent are used by at least 351 species, although only 2.7% of birds occurring in the subcontinent breed in rice fields. The spread of rice cultivation and its attendant secondary habitats may have contributed to the increase in range and population of 64 common species but is threatening hundreds of other species, many of conservation concern. Most work in the region has focused on birds as pests of rice. Few studies have been conducted on the habits of birds that use rice fields and fewer still have compared how rice fields and similar natural habitats differ. Although rice harvesting has caused nest mortality for breeding birds, there is no comparable information from natural habitats. The guild structure of birds in rice fields is similar to that overall in the region except for a higher representation of carnivores. Rice fields are used primarily by grassland and wetland species. There are large information gaps that require filling to be able to ascertain the utility or impact of rice fields to bird populations and, thus, many research opportunities.
Rice (Oryza sativa) growing in Australia occurs almost exclusively in the south-east, in the Riverine Plains of the Murray-Darling Basin, with an annual average of 110,000 ha. All crops are grown under irrigation using water abstracted from rivers. Rice fields are flooded between October and March and are dry otherwise. A large decrease in natural wetland extent and declines in most waterbird populations have been associated with the increase in irrigated agriculture since the 1960s. The ecology of waterbirds in rice fields has been studied in only one area, around Fivebough Swamp in southern New South Wales. Thirty-seven waterbird species were recorded in rice fields compared with 70 species on an adjacent natural wetland. Species diversity and the abundance of individual species declined as the rice crops developed so that most species used rice fields for only one to two months after flooding. An increase in water depths associated with the timing of panicle initiation of the rice plants was probably the main cause, but declines in most waterbird prey species also occurred as the crops developed. Rice crops were particularly important feeding areas for Glossy Ibis (Plegadis falcinellus) during November and December. Small numbers of the threatened Australasian Bittern (Botauins poiciloptilus) were also recorded.
In southern Europe, rice (Oryza sativa) is one of the most important agricultural crops. Relationships between rice fields and bird occurrence are well studied for some taxa while quantitative data are lacking for other, more secretive, species. Rice cultivation may be important in the conservation of some threatened birds; for example, agricultural flooded areas in northwestern Italy support 25% of the Italian population of Eurasian Bittern (Botaurus stellaris) although variation in farming techniques affect the suitability of fields for birds. Agricultural practices that benefit birds include avoiding intermittent flooding or dry cultivation, maintaining stubble during winter, allowing some weed patches to persist inside fields and along ditches and conserving natural vegetation in rice field landscapes. Additionally, biological and alternative cultivation methods seem to provide better environmental conditions compared to traditional methods. To promote environmental and conservation values of rice fields, BirdLife International coordinates a project throughout Europe for expanding environmentally-friendly rice cultivation. In some regions, rice fields are the only habitat available for wetland birds due to the scarcity or poor quality of natural wetlands. Despite interest in African and Middle Eastern birds and the geographical proximity of these areas to Europe, knowledge of birds and rice fields there is extremely limited. The fact that these regions are located along some of the most important migration routes in the Old World suggests that their rice fields may be used by large numbers of waterbirds.
Rice fields in West Africa comprise mangrove swamp rice and rain-fed rice cultivations along the coast, rice fields in floodplains and river valleys, and inland irrigated cultivations. All these rice systems constitute important habitats for African and migratory Palaearctic waterbirds. Density counts reveal the presence of about 16 wetland-related birds per ha during the northern winter if the habitat is still damp or covered by water; this declines to about four birds/ha if the fields are dry. The coastal rice fields (South Senegal-Guinea-Conakry) harbour 1.17 million wetland-related birds during the northern winter, and the inland rice fields of Office du Niger (Mali) contain 730,000. In former floodplain areas, the high bird numbers in rice fields offer, to some degree, an ecological compensation for the loss of floodplains. In the Inner Niger Delta, for example, the construction of the Selingue Dam and the Office du Niger irrigation scheme resulted on average in the loss of 12 % of the wintering waterbirds. However, the ecological loss is larger than these numbers suggest because most bird species in irrigated rice fields are common, while rare and endangered species are concentrated in the remaining West African floodplains that have not been converted to cultivated rice fields.
Rice (Oiyza sativa) is cultivated in 21 countries throughout North, South and Central America, and the Caribbean. Waterbird and landbird use of rice paddies in the Americas was evaluated. Information was compiled on birds and rice habitats from Argentina, Brazil, Colombia, Costa Rica, Cuba, Surinam, Trinidad and Tobago, Uruguay, USA and Venezuela. At least 169 waterbirds belonging to 21 families and 166 landbirds have been recorded in the paddies of the region. Anatidae was the best represented family, followed by Scolopacidae, Rallidae and Ardeidae; 67% of species belonged to these four families. Western Cattle Egret (Bubulcus ibis), Western Great Egret (Ardea alba), Snowy Egret (Egretta thula), Black-crowned Night Heron (Nycticorax nycticorax), Lesser Yellowlegs (Tringa flavipes) and Greater Yellowlegs (Tringa melanoleuca) were reported in all countries, but relative abundances varied. During the rice-growing cycle, fields were most important for carnivorous birds during the sowing stage, whereas post-harvest flooded fields were most valuable for granivorous waterbirds. Of 92 genera recorded, 28 had sympatric species. In general, geographically proximate countries were most similar in the composition of bird species using their paddies. In all countries, rice fields are considered important feeding areas and heavily used as migratory stop-over and wintering sites.
Important and unique breeding bird communities occur in rice fields throughout the world, but little is known about breeding densities and nest success, and, therefore, the value of rice fields to breeding birds. Breeding bird use of rice fields is divided into five categories: 1) nesting in standing rice crop, 2) nesting on levees within fields or at field perimeters, 3) nesting in associated irrigation canals and ditches, 4) nesting in other wet areas that exist because of rice cultivation, and 5) use of fields for foraging, while breeding in adjacent habitats. Nest density and nest success vary greatly based on the region, management practices, and species' requirements. Birds commonly nesting in rice fields include ducks, bitterns, rails, shorebirds, terns and some passerines. Herons often use rice fields heavily while breeding in adjacent habitat. Research on nest densities, nest success, nestling and fledgling success, and microhabitat selection is needed to better understand the bird communities that use rice fields.
Worldwide, rice (Oryza sativa) agriculture typically involves seasonal flooding and soil tillage, which provides a variety of microhabitats and potential food for birds. Water management in rice fields creates conditions ranging from saturated mud flats to shallow (<30 cm) water, thereby attracting different guilds of birds. Grain not collected during harvest (i.e. waste rice) is typically the most abundant potential food of birds in rice fields, with estimates of seed mass from North America ranging from 66–672 kg/ha. Although initially abundant after harvest, waste rice availability can be temporally limited. Few abundance estimates for other foods, such as vertebrate prey or forage vegetation, exist for rice fields. Outside North America, Europe and Japan, little is known about abundance and importance of any avian food in rice fields. Currently, flooding rice fields after harvest is the best known management practice to attract and benefit birds. Studies from North America indicate specific agricultural practices (e.g. burning stubble) may increase use and improve access to food resources. Evaluating and implementing management practices that are ecologically sustainable, increase food for birds and are agronomically beneficial should be global priorities to integrate rice production and avian conservation. Finally, land area devoted to rice agriculture appears to be stable in the USA, declining in China, and largely unquantified in many regions. Monitoring trends in riceland area may provide information to guide avian conservation planning in rice-agriculture ecosystems.
Literature is reviewed to determine the effects of landscape features on waterbird use of fields in regions where rice (Oryza sativa) is grown. Rice-growing landscapes often consist of diverse land uses and land cover, including rice fields, irrigation ditches, other agricultural fields, grasslands, forests and natural wetlands. Numerous studies indicate that local management practices, such as water depth and timing of flooding and drawdown, can strongly influence waterbird use of a given rice field. However, the effects of size and distribution of rice fields and associated habitats at a landscape scale have received less attention. Even fewer studies have focused on local and landscape effects simultaneously. Habitat connectivity, area of rice, distance to natural wetlands, and presence and distance to unsuitable habitat can be important parameters influencing bird use of rice fields. However, responses to a given landscape vary with landscape structure, scale of analysis, among taxa and within taxa among seasons. A lack of multi-scale studies, particularly those extending beyond simple presence and abundance of a given species, and a lack of direct tests comparing the relative importance of landscape features with in-field management activities limits understanding of the importance of landscape in these systems and hampers waterbird conservation and management.
The effect of rice cultivation on waterbird populations has rarely been assessed. A study in northwestern Italy estimated that breeding herons and egrets obtained 80% of their food from agricultural habitats. The estimate was checked by comparing the occupation of three contiguous sectors of northwestern Italy, one with mainly rice fields, a second with planitial rivers and a third with small upland rivers, from 1982 to 2002, a period in which breeding populations increased. During the increase, the breeders expanded into the second and third sectors only when their population exceeded a certain level, in accordance with predictions of the “ideal free” model of habitat selection. The initial estimate of the importance of rice cultivation is confirmed by this long-term comparison, with the “rice fields” sector hosting 76% of the population. The long-term analysis cautions against generalizations from instantaneous surveys, which can estimate the differential profitability of habitats but not their carrying capacity, unless habitat availability limits population size. Additional information is needed to predict waterbird population responses to environmental change; topics include: habitat use, particularly in Asia; landscape effects; prey availability, foraging intake and behavior; demographic parameters such as breeding success, survival, settlement patterns, site fidelity, and temporal variance; and population changes in relation to management practices.
Most literature on birds and rice (Oryza sativa) focuses on the non-growing period and little is known about the influence of management practices during cultivation. A review found that the main factors affecting species composition and abundance in rice fields during the growing season were water level, flooding period, rice plant structure and size, and pesticide use. Highest bird density and diversity occurred at intermediate water levels (10–20 cm). Early flooding and late drying favored waterbird density and diversity, and the stopover of migrating species. Taller plants, at higher densities, reduced prey availability to most waterbirds but favored smaller species. Pesticides and herbicides have been shown to be toxic to birds and reduce food resources. A case study is presented for the Ebro delta, Spain. Three management schemes were compared: organic, agri-environmental and conventional. Bird density, biomass and diversity throughout the growing and non-growing seasons were determined in three consecutive years. Bird biomass, density and diversity averaged higher in the organic rice fields, but only biomass was significantly different. The higher biomass reflects the presence of a higher biomass of prey items (fish, invertebrates and macrophytes) in the organic rice fields, likely due to the lack of pesticides. Further research should focus on a quantitative assessment of the effects of specific management practices.
Fields planted with rice (Oryza sativa) are used by a wide variety of bird species during the non-growing season and play an important conservation role in many parts of the world. Management of fields affects the variety and number of birds that use them, and a thorough understanding of these issues could improve the conservation value of rice farming. The challenge for conservation practitioners is identifying management actions that provide benefits, without adverse impacts on crop production. Harvest method, post-harvest straw management, winter flooding, food supplementation and hunting all influence bird populations. Also, field preparation methods, organic farming and the management of field margins and drainage ditches, probably influence the conservation value of rice agriculture but have received less attention. Current knowledge of these issues is reviewed in order to identify management practices thought to have conservation benefits and highlight topics that warrant additional research.
Waterbird use of agricultural wetlands has increased as natural wetlands have declined. Use of rice (Oryza sativa) habitats by some waterbird species is considered essential to sustaining populations. Although use of rice habitats by waterbirds has been documented throughout the world, little information is available on potential risks as a result of chemicals used in rice cultivation. The current review summarizes understanding of the use and consequences to birds of pesticide applications in rice habitats. Historically, organochlorine pesticides known to be applied for pest management in rice cultivation included dichlorodiphenyltrichloroethane (DDT), aldrin, dieldrin, endrin, heptachlor, technical hexachlorocyclohexane (HCH), toxaphene, endosulfan and sodium pentachlorophenate. Endosulfan and purified HCH (the gamma isomer lindane) are still in use. Cholinesterase-inhibiting insecticides currently used in rice include carbofuran, monocrotophos, phorate, diazinon, fenthion, phosphamidon, methyl parathion and azinphos-methyl—many products known to cause acute poisoning in birds. In addition, herbicides, fungicides, molluscicides and other pesticide types are used in rice cultivation. Some of the chemicals are highly toxic to birds and associated with mortality; several have the potential of causing adverse reproductive effects. Because of the large area under rice cultivation worldwide, the volume of pesticides applied to rice fields is significant. Innovations within the past few decades in rice production have increased pesticide use resulting in biodiversity losses in production areas and pollution of water resources. Management practices that address adverse effects of pesticide use in rice fields include increased adoption of Integrated Pest Management principles and less toxic products.
Wild waterfowl are the reservoir for avian influenza viruses (AIVs), a family of RNA viruses that may cause mild sickness in waterbirds. Emergence of H5N1, a highly pathogenic avian influenza (HPAI) strain, causing severe disease and mortality in wild birds, poultry and humans, had raised concerns about the role of wild birds in possible transmission of the disease. In this review, the link between rice production systems, poultry production systems, and wild bird ecology is examined to assess the extent to which these interactions could contribute towards the persistence and evolution of HPAI H5N1. The rice (Oryza sativa) and poultry production systems in Asia described, and then migration and movements of wild birds discussed. Mixed farming systems in Asia and wild bird movement and migration patterns create opportunities for the persistence of low pathogenic AIVs in these systems. Nonetheless, there is no evidence of long-term persistence of HPAI viruses (including the H5N1 subtype) in the wild. There are still significant gaps in the understanding of how AIVs circulate in rice systems. A better understanding of persistence of AIVs in rice farms, particularly of poultry origins, is essential in limiting exchange of AIVs between mixed-farming systems, poultry and wild birds.
Considerable work has been done to investigate linkages between the production of rice (Oiyza sativa) and bird ecology and conservation. Rice is an extremely important crop globally and affects waterbirds in diverse ways. Rice fields are not substitutes for natural wetlands but are used by many species and can help mitigate the loss of natural habitats in areas where agriculture dominates. Most birds use rice fields primarily for foraging, but some—including rare species—also nest in rice. Field management affects birds in numerous ways, some of which have been studied in detail, but most of which have not. Increasing collaboration between researchers, farmers and agronomists provides opportunities to better understand how field management can be modified to increase the conservation value of fields without compromising the economic viability of farming. Such research would facilitate the development of well-designed agri-environment schemes and provide a solid basis for marketing “wildlife-friendly” rice products. Other major topics where future research is needed include: nesting and post-fledging success; availability and value of foods other than rice grain that are found in fields; importance of field edges and water delivery infrastructure; influence of landscape features; effects of rice farming on population dynamics; experimental studies of management activities, especially at large spatial scales, in tropical regions, and during the breeding season; and an improved understanding of how socio-economic factors influence the ecology and conservation of the wetland birds that use rice fields.