|Managing Wetlands for
Waterbirds: How Managers Can Make a Difference in Improving Habitat to Support a North
American Bird Conservation Plan
R. Michael Erwin1, Murray K. Laubhan2, John E. Cornely3, and Dana M. Bradshaw4
Although wetlands are widely recognized as among the most productive ecosystems globally, wetland loss continues both in North America and throughout the world, owing largely to a burgeoning human population and the concomitant conversion of natural wetlands for human uses. For example, the Bay of Fundy is a critical habitat for shorebirds during migration (Morrison et al. 1994) but is threatened with both hydroelectric development and harvesting of polychaete worms (major shorebird prey) for sport fishing (P. Hicklin, Canadian Wildlife Service, pers. comm.). Similarly, James and western Hudson Bays are the subjects of major water development planning, despite their roles as major nesting and migration areas for geese and a number of species of shorebirds. The prairie pothole region of Saskatchewan and Manitoba are part of a Canadian prairie habitat joint venture (JV) under the North American Waterfowl Management Plan (NAWMP[USFWS 1986]). The region has been recognized internationally as one of the premier nesting grounds for many diving and dabbling ducks, and it also provides habitat for endangered Piping Plovers (Charadrius melodus). This area historically has faced numerous conversions of potholes to croplands. The western Canadian regions of most concern are the Fraser River corridor and delta and the adjacent Vancouver Island region. Development and growth is rapid in that region, and intense logging occurs along the Fraser. The region is well known for its wintering waterfowl and marine bird concentrations (Vermeer and Butler 1989). Similar examples are numerous throughout most of North America. However, during the past two decades, many federal, provincial, and state programs have been initiated to provide economic incentives for wetland conservation in an attempt to achieve a "no net loss" of wetlands (The Conservation Foundation 1988). These earlier losses of wetlands, and recent changes in the status of wetlands, have broad implications to wildlife.
In this paper we review the status of wetlands as habitats for waterbirds (defined as waterfowl, colonial waterbirds, shorebirds, and rails and allies). We focus on species whose status is of concern either regionally or nationally, and on current wetland management practices that are detrimental to wetland birds. We identify gaps in our knowledge of ecological principles for managing habitats for waterbirds, and conclude with recommendations for improving wetland management to enhance waterbird populations.
STATUS OF SPECIES AND ASSOCIATED WETLANDS
We consulted two recent publications to identify the major waterbird species of concern in North America: The 1994 list of endangered and threatened wildlife and plants (USFWS 1994) and the 1995 List of Migratory Nongame Birds of Management Concern (Office of Migratory Bird Management [OMBM] 1995). These lists indicate that more than 50% of birds of concern in the U. S. are associated with either wetlands or aquatic habitats (Table 1; Canada and Mexico do not have formal endangered species listings). The federal endangered and threatened list includes 16 of 35 species (not including Hawaii or trust territories) that are wetland or aquatic-dependent, while the comparable figures from the OMBM list are 14 of 23 species.
Table 1. List of wetland/aquatic bird species of concern in the United States.
1"Aquatic" refers to primary use of lake, river, and/or marine habitats.
2United States Fish and Wildlife Service (1994).
3Office of Migratory Bird Management (1995).
The habitats used by these species suggest that the majority are associated with freshwater (interior) marshes or coastal beaches and/or islands. These are habitats that have been among the most affected by humans, either by direct disturbance (beaches) or indirectly by agricultural conversions (freshwater marshes). In addition, interior marshes and coastal areas often are intensively managed, suggesting that current habitat management practices should be evaluated relative to providing benefits to a diversity of species. For example, many of the major wetland complexes listed for the U. S. already are included under JVs in the NAWMP (Table 2). However, the Atlantic Coast Habitat Joint Venture focuses on American Black Ducks (Anas rubripes). Separate (but unequal) programs are directed at restoration of the endangered Piping Plover, and at monitoring certain declining colonial waterbird species in the mid-Atlantic barrier region.
Table 2. Primary wetland regions for waterbird conservation in North America.
1Designated as a Faunal Reserve or international Man and Biosphere Reserve (UNESCO).
During the past decade, however, the scope of habitats and avian species being considered has been increasing. For example, discussions are under way (C. Hunter, USFWS, pers. comm.) to form a JV for part of the extensive forested wetlands in the southeastern U. S. from Virginia to Florida where forested wetland loss has resulted in marked declines of wintering waterfowl and certain songbirds such as the Swainsons Warbler (Lymnothlypis swainsonii). The lower Mississippi River supports a very active JV that includes waterfowl, shorebirds, and Neotropical migrants. In the interior, agriculture has been modified to be more "friendly" to wetland birds in several JV areas: The Playa Lake region of Texas and southern Colorado, the Prairie Potholes of the Dakotas and Montana, and the Rainwater Basins in Nebraska. The Playas are important waterfowl wintering habitat, while the latter two areas are critical for breeding and migrating waterfowl and shorebirds.
Farther west, the riparian corridors of the arid intermountain west and the large agricultural valleys (e.g., Central, Sacramento, and San Luis in California, and Willamette in Oregon) represent important wintering and migration habitat for waterfowl and shorebirds, respectively. Metal contamination (selenium and boron) of irrigation drainwater in the agricultural basins of the West has stirred major controversies concerning whether wetlands in wildlife refuges should become sumps. Along the west coast, the few estuaries with remaining wetlands (San Francisco Bay, San Diego Bay, Puget Sound, Fraser River delta and corridor) require constant vigilance to protect against further loss and degradation. Recently, the USFWS named Puget Sound as a national estuary program.
In Alaska, numerous wetlands abound both on the coast and on interior wildlife refuges and parks; most of these are under no immediate threats. The major exception is the Arctic National Wildlife Refuge, which some U. S. congressmen refer to as the Alaska Oil Reserve. Special mention also should be made of the Copper River delta, which is critical to enormous numbers of migrating shorebirds in spring and fall (Gill et al. 1995). It also is important to many species of geese and ducks.
In Mexico, a number of important wetland areas for waterbirds, especially waterfowl, have been identified under the NAWMP. To date, however, none has been designated as a JV area (USFWS 1995). Several, however, have been designated by UNESCO as Man and Biosphere Reserves or as Faunal Reserves by Mexico (Baldassarre et al. 1989; Table 2). Of hemispheric importance is the Usumacinta-Grijalva delta region, which exceeds the size and significance of the present-day Everglades region in Florida (Ogden et al. 1988). It is threatened by conversion to agricultural uses and dam construction. The northern coastal lagoons of Rio Lagartos and Rio Celestun are important to the rare Greater Flamingo (Phoenicopterus ruber) and are major wintering areas for several species of waterfowl migrants from the U. S.
WETLAND PRACTICES UNFAVORABLE TO WATERBIRD CONSERVATION
In this section, we highlight some current practices occurring in wetlands that adversely affect either the quality or quantity of wetland habitat available to waterbirds (see Table 3). The principal areas affected also are indentified. Where possible, we make recommendations for improvement.
Table 3. Wetland practices unfavorable to waterbirds and wetland conservation in North America.
Navigation and flood control. The hydrology of many rivers has been severely modified. In many cases, peak discharges have been reduced and low flows have been increased, resulting in more stable hydroperiods among seasons and years. Although moderation of flows improves efficiency of hydroelectric power generation, provides more reliable navigation, and reduces the threat of floods, many habitats important for avian species have been destroyed or their value severely decreased. However, recent attempts to coordinate water discharges to facilitate reestablishment of riparian wetland types and regeneration of woody riparian species have met with some success. Additional effort should be directed toward cooperation among responsible agencies and individuals with respect to alternative methods of river management.
Human disturbances along beaches and islands in the coastal barrier regions. Increases in population and recreational demands by boaters continue, especially in the Atlantic and Gulf coasts of the U. S. In the Yucatan region of Mexico, resort development and ecotourism continue to grow. Increasing access to formerly remote mangrove islands by personal watercraft (e.g., Jet Skis) represents an increasing threat to nesting herons, spoonbills, storks, pelicans, and cormorants in Florida, Texas, Mexico, and other tropical coastal resort areas (Erwin et al. 1995, Rodgers and Smith 1995). These threats call for additional regulatory actions regarding land access as well as environmental education, especially for boaters who may be oblivious to bird conservation needs.
Mosquito control in coastal marshes. Historically, coastal marshes were diked to stabilize water levels, thereby reducing the magnitude of mosquito problems. Current mosquito control in most coastal areas combines use of organophosphate pesticides as adulticides with some form of marsh management. The latter often involves use of heavy equipment to create high-marsh ponds and canals that allow fish to access mosquito breeding areas (Meredith and Stachecki 1985). Although this practice may be ecologically superior to using dikes and chemical pesticides, in many areas the net benefit to waterbirds and other wildlife may be marginal at best (Erwin et al. 1994). Because few natural coastal marshes remain along the east and Gulf coasts of the U. S., marsh manipulations should be restricted to those areas that already have been severely altered by humans, and where mosquitoes are a major nuisance.
Timber harvesting on private lands. Especially in Canada and the southeastern U. S., timber harvesting in palustrine forested regions has resulted in large losses of wetlands for wildlife (Erwin 1996). In addition, many remaining forested wetlands have been fragmentedor natural hydrologic regimes have been disruptedby road construction for timber harvesting. Conservation organizations need to develop partnerships with private organizations and corporations to determine market-compatible methods of extraction that are more "friendly" to wildlife. This effort also will require more education of "corporate America" (as well as corporate Mexico and Canada) about the values of biodiversity.
Single-species management in forested wetlands. Wildlife management in forested wetlands of the Mississippi River corridor and throughout much of the south and northeastern U. S. has concentrated on "greentree reservoirs" where the primary focus has been to produce Wood Ducks (Aix sponsa) (Fredrickson et al. 1990). The Wood Duck has been a major "target species" for both state and federal refuge lands. Although "woodies" have become increasingly important to waterfowl hunters as other species have declined over the past decade, managing for one species is usually accomplished at the expense of many others in the ecosystem. Within a complex of impoundments, managers should seek to diversify water management schedules to maintain current forest composition and structure as well as to promote natural regeneration.
Grazing in riparian zones along western rivers. Exclosures or other methods of preventing livestock access to free-flowing rivers of the arid west are essential to ensuring stream water quality and to resisting further invasions of exotic plants. This problem is critical in the western U. S. (Naiman et al. 1995) and especially western Mexico.
Water rights of wildlife. In the western U. S. and prairie regions of Canada, water rights among state, provincial, and local interests are politically charged. Wetland managers need to argue that wetland wildlife also has a "share" in this essential commodity, and that refuges should not simply become shunts for receiving irrigation drainwater that will adversely affect water quality. Concentrations of metals (e.g., selenium) in drainwater in vast regions of the arid western U. S., from California across Nevada to Wyoming, have compromised the wildlife quality of many refuge wetlands and other non-federal impounded wetlands (Ohlendorf et al. 1986).
Protecting small pothole complexes in the prairie regions. In Canada and the U. S., valuable gains have been made to set aside marginal agricultural lands for wildlife. Further efforts are needed to insure that large complexes of these small wetlands are maintained to conserve the diversity of habitat needed by nesting waterfowl, shorebirds, rails, and grebes. Farmers must have continued financial incentives (e. g., the Conservation Reserve Program under the Food Act of 1985) to maintain the successes achieved to date. The lessons learned in Canada and the U. S. need to be applied in Mexico, where farmers presently have few economic incentives to save wetlands.
Runoff and sedimentation. In the Playa Lakes region in Oklahoma, west Texas, and southeastern Colorado, water quality suffers in many areas due to feedlot manure runoff and sedimentation into the lakes from livestock areas. More effective buffering is needed. Cotton crops are ecologically dangerous because of the intensive pesticides they require, and because of soil erosion resulting from lands left barren much of the year. Alternative land uses are advised.
Pesticides. Modern organophosphate pesticide applications, although not as toxic as organochlorines (Grue et al. 1983), are still problematic throughout most agricultural areas in North America. In the Rainwater Basins of Nebraska, in addition to heavy pesticide applications, a number of exotic plants also have invaded. More biological control of pest species is strongly encouraged. Water quality in these small basins has suffered.
MAJOR GAPS IN OUR KNOWLEDGE TO EFFECTIVELY MANAGE WETLANDS FOR WILDLIFE
We identify below some major gaps in our understanding of wetland wildlife and its habitat needs, how wetlands function as quality wildlife habitat, and how to more effectively integrate and communicate our knowledge to managers and the public.
Integration of wetlands within the landscape matrix. Often, studies of habitats have focused only on the individual habitat type: Wetlands, grasslands, forest type, and so forth. Further, information regarding differential use of wetland types by wetland-dependent species is lacking. Little attempt has been made to determine how the juxtaposition of various wetland or habitat types affects their respective uses by wildlife. Research is required to determine how local (e.g., wetland complex) and regional (e.g., flyway) landscape processes affect patterns of use.
Regional and national monitoring of populations. Wintering locations of most waterfowl have been identified as part of the regular inventory of states and USFWS flyway councils. The major shorebird concentration areas have been identified by the Western Hemisphere Shorebird Reserve Network (WHSRN, Myers et al. 1987), now part of the larger Wetlands for the Americas Program. Although songbirds are well monitored by the annual roadside Breeding Bird Survey, wetland species are much less covered because of lack of road access to most wetland areas. The International Shorebird Survey is undergoing a review (B. Harrington, pers. comm.) and a colonial waterbird national database is under development within the Biological Resources Division of the U. S. Geological Survey (BRD) since the National Audubon Society database was terminated in the late 1980s. A marsh bird (rails, bitterns, grebes) survey has been under discussion within BRD (S. Droege, USGS, pers. comm.) because of the dearth of information on this group of birds, some of which are hunted annually. Currently much less information is available on either migration concentration areas or on important wintering sites of colonial waterbirds, rails, and bitterns. All of these major groups are lacking in comprehensive survey coverage to allow for national assessments of trends in populations.
Fragmentation effects. Although the effects of forest fragmentation have been well studied for upland bird species (see Askins et al. 1990 for a review), much less information is available on the effects of wetland fragmentation. Research is required to investigate how changing sizes and patterns of distinct wetlands (e.g., potholes) affect their use by a variety of wetland birds. In addition, the fragmentation of expansive areas of marshes (e.g., by mosquito control excavation) may adversely affect their use as breeding habitat for some species (Burger et al. 1979, Erwin et al. 1994).
Large-scale experimentation in wetland management. Seldom are well-controlled experiments performed in wetlands. Impoundment water management, pesticide applications, Phragmites control, mosquito ditching, and marsh burning all are examples of activities for which controlled and replicated experimentation is needed to critically evaluate different management practices in wetlands. These approaches should follow an adaptive resource management strategy (Walters 1986; Conroy, this volume).
Training of professionals. Many private, state, provincial, and federal biologists and managers involved in either the conservation or regulation of wetlands possess only a basic understanding of wetland ecology. More advanced training is required to understand the ecological processes in wetlands and to understand the significance of wetland complexes over a larger landscape. Geographic information systems are becoming vital tools for managers to learn the basics of ecosystem and landscape management.
Public relations concerning wetlands. For the public to appreciate attempts to conserve wetlands, much more emphasis must be placed on teaching the values of wetlands to the citizenry of Canada, the U. S., and Mexico (Conservation Foundation 1988). Especially considering the anticipated demands for fresh water (water consumption in the U. S. has doubled since the 1940s and may double again in the next 20 years [Naiman et al. 1995]), the public must develop an appreciation of wetlands for the many ecological, recreation, aesthetic, and public service values that they hold. Teaching of wetland ecology should be included in public school curricula, and should be part of the outreach effort of every scientist and landscape manager.
Our general recommendations to improve wetland management for a wide array of waterbird species are as follows:
* The current JVs in the U. S. under NAWMP should be expanded to include more non-waterfowl avian species. The Canadian prairie habitat JV and the Lower Mississippi Valley JV have significant shorebird components. They also could be expanded to include colonial waterbirds, rails, and bitterns. A single-species or focal-group approach will achieve only limited success.
* New JVs and other partnerships should be established in regions with no current JVs; this includes all of Mexico, parts of eastern Canada, and the southeastern U. S., although the forested wetlands of the southeastern coastal plain are receiving attention (C. Hunter, USFWS, pers. comm.).
* Criteria should be developed for reaching resource goals for JVs. Are population goals feasible to set? Are habitat area goals sufficient? How are quality criteria set?
* Inventories should be supported to determine waterbird status in critical wetlands, especially for little-studied species. Concentration hotspots for colonial waterbirds or rails could result in designations similar to those used by WHSRN (i.e., sites of international, hemispheric importance).
* Training workshops for wetland biologists and managers should be expanded and should include the private sector. Aquaculturists, rice farmers, hunting preserve managers, large ranch owners, and leaders of ecotourism enterprises should be included in the educational process.
* Assistance in ecological planning for wetland construction or alteration needs to be institutionalized. As part of a permitting process, regulatory personnel in state, provincial, and federal governments should require that a private permit holder consult with professional wetland scientists (certified by the Society of Wetland Managers) before embarking on large-scale wetland projects such as construction of reservoirs, aquaculture facilities, or irrigation systems. For example, if catfish ponds in the south had been constructed as small (half-acre) ponds, then bird exclosures would have been easier to construct to preclude cormorant and heron damage. This information could have been provided by a professional who is knowledgeable about waterbird biology.
We thank Marcia Wilson and Bentley Wigley for advice in the development of this paper. Useful comments were provided by M. Haramis, D. Pashley, M. C. Perry, and D. Sparling.
Resources Division, USGS
Resources Division, USGS
3 U. S. Fish &