By Matt Young
The wetlands of Mexico are the final migration stop for millions of waterfowl and other migratory birds from across North America
There is perhaps no better place to see birds than from a duck blind on a lagoon along the Pacific Coast of Mexico. Peering through a thin screen of mangrove branches, my hunting partners and I marveled at the sight of thousands of ducks and other waterbirds streaming across the sky above the estuary. Waves of wigeon and pintails, returning to the coast from feeding in irrigated grainfields far inland, sailed lazily over the tidal flats, filling the air with their soft whistling calls.
Swarms of green-winged and cinnamon teal buzzed low across the water, and single-file processions of fulvous and black-bellied whistling ducks traded between their roosts in copses of flooded mangrove trees. They were followed by flights of shovelers, redheads, canvasbacks, scaup, and Mexican ducks, as well as brown and white pelicans, roseate spoonbills, and dozens of species of shorebirds, gulls, terns, and herons.
As I saw firsthand during my duck hunt in Sonora several years ago, the wetlands of Mexico provide critical wintering habitat for waterbirds from across North America. According to surveys conducted by the U.S. Fish and Wildlife Service, Mexico supports more than 15 percent of the continent's ducks and geese during the fall and winter months. This includes nearly the entire population of Pacific black brant, 85 percent of North America's blue-winged teal, 33 percent of its redheads and shovelers, 25 percent of its American wigeon, 20 percent of its green-winged teal and white-fronted geese, and 15 percent of its pintails. In total, 38 species of ducks, geese, and swans occur in Mexico, either as seasonal visitors or permanent residents.
"The migration habits of waterfowl require Ducks Unlimited to work throughout North America, including in Mexico, where many of our ducks and geese spend the winter," says John E. Walker, president of Ducks Unlimited of Mexico (DUMAC). "DUMAC's role in Mexico is especially important because many of that nation's most important wetlands are threatened, and limited resources are available to conserve them."
Concern about the loss of waterfowl habitats south of the border led to the creation of DUMAC in 1974. The first organization of its kind established in Mexico, DUMAC pioneered efforts to conserve the nation's wetlands and wildlife, and, today, is the country's leading nongovernmental wetlands conservation organization. Like its DU counterparts in Canada and the U.S., DUMAC delivers on-the-ground wetland conservation projects in cooperation with many government agencies, foundations, corporations, other conservation organizations, and private landowners. DUMAC also has been instrumental in mapping and classifying Mexico's most important wetland systems, and supports a variety of research, evaluation, and monitoring of the nation's waterfowl and their habitats.
In the public policy arena, DUMAC's Executive Director, Eduardo Carrera, serves as chairman of a national subcommittee on the conservation of wetlands and waterfowl. This group directly advises Mexico's federal government on programs and policies of critical importance to DU's mission, including the development of a national conservation plan for waterfowl and their habitats, implementation of the North American Waterfowl Management Plan, and delivery of conservation projects funded by grants from the North American Wetlands Act (NAWCA), U.S. Fish and Wildlife Service, U.S. Forest Service, and other national and international partners.
The wetlands of Mexico face many threats as a rapidly growing human population fuels an ever increasing demand for food, freshwater, and living space. The rapid expansion of agriculture, industry, and urban sprawl claims thousands of acres of wetlands and associated uplands in the country each year. To maximize limited conservation resources, DUMAC carefully targets its conservation work in the most valuable and threatened wetland ecosystems. The following is an overview of the regions of greatest importance to waterfowl in Mexico, and DUMAC's programs to conserve wetlands and associated uplands in these areas.
Mexico's Pacific Coast—bordering the Gulf of California on the Baja Peninsula and in the states of Sonora, Sinaloa, and Nyarit—is the country's most important waterfowl wintering area. Millions of waterbirds flock to the region's extensive networks of wetlands, consisting of tidal estuaries bordered by brackish lagoons and mangrove swamps, and sprawling inland freshwater emergent marshes and reservoirs. Collectively, these habitats support roughly one-third of Mexico's wintering waterfowl, including nearly the entire continental population of Pacific black brant, and even greater numbers of shorebirds, such as avocets, long- and short-billed dowitchers, western sandpipers, and stilt sandpipers.
Historically, grain crops cultivated on the adjacent coastal plain provided important food resources for wintering waterfowl in the region. Rice grown in the state of Sinaloa is particularly attractive to wintering waterfowl, and the distribution of ducks, especially pintails, is strongly influenced by the acreage of rice that is planted each year. DUMAC surveyed more than 1 million pintails wintering in Sinaloa during the mid-1980s, when 300,000 acres of rice were grown there. However, the abundance of pintails and other dabbling ducks in the region has declined markedly as the majority of rice acreage has been converted to vegetable crops or has been taken out of production. In an effort to replace the loss of rice acreage, DUMAC is planning to work with private landowners in Sonora and Sinaloa to restore wetlands on former croplands, using surplus irrigation water.
Until recently, most of Mexico's Pacific coastal wetlands remained largely untouched by development. However, the expansion of the commercial shrimp-farming industry has emerged as a serious threat to these critical habitats. Shrimp are raised in impoundments constructed in fresh- or brackish water marshes that are flushed with seawater channeled from the Gulf. The salt water kills vegetation in the impounded marsh and eventually converts productive waterfowl habitat into barren, saline waters. In Sinaloa, for example, shrimp farming already has degraded more than 50,000 acres of wetlands. The continued expansion of the industry along the Pacific Coast would claim far more waterfowl habitat. In response to this threat, DU biologists are proposing the development of a manual to help shrimp farmers manage their farms in a manner that will minimize impact on wetland habitats.
DUMAC also continues to work with Mexico's federal government to seek permanent protection of areas of particular importance to waterfowl and shorebirds. In recent years, DU biologists have conducted groundbreaking surveys documenting waterbird populations along Mexico's Pacific Coast. This information was instrumental in the successful effort to gain international recognition of the region's most important estuaries—Ensenada del Pabellon and Bahia Santa Maria in Sinaloa—as Western Hemisphere Shorebird Reserve Network sites.
DUMAC also is seeking protection of bays and estuaries along the Baja Peninsula that provide critical wintering habitat for Pacific brant and, coincidentally, serve as calving grounds for large numbers of gray whales. The scenic coastline adjacent to these waters is highly vulnerable to development. During the past decade, DU has teamed with several partners to map and inventory critical waterfowl habitats along the Baja Peninsula, and is encouraging the Mexican government to designate these areas as wildlife reserves. The creation of one such reserve at Laguna de Scammons helped save a critical brant wintering area from development.
DUMAC is actively working to conserve wetlands in other high-priority areas of western Mexico. For example, DUMAC has joined government agencies and private landowners to restore and enhance critical wetlands in the Colorado River delta, just south of the U.S. border. Historically, the Colorado River delta encompassed nearly 2 million acres of highly productive wetlands that supported some of the largest concentrations of wintering waterfowl in the Pacific Flyway. However, nearly all the water that once flowed to the delta has been diverted for other uses, causing the majority of this once vast wetland complex to go dry. As a result, remaining wetlands in the region are especially important to wildlife. On DUMAC's recently completed El Doctor project, cattle fences were constructed, surrounding 383 acres of critical spring-fed wetlands and providing much-improved habitat for thousands of migrating and wintering waterfowl and shorebirds.
Situated on the vast Mexican Plateau, the Interior Highlands of northern and central Mexico is a high, arid region composed of large ranches and farms. As in the American Intermountain West, water is a scarce commodity in this region, and tremendous numbers of wintering and resident waterfowl rely upon its limited wetland habitats. Waterfowl surveys conducted by the USFWS have identified seven key wetland systems in the Interior Highlands. Critical waterfowl habitats in the region include large lakes, extensive emergent marshes, and shallow seasonal wetlands.
The Interior Highlands is especially important to geese and dabbling ducks. Roughly 10 percent of the approximately 200,000 white-fronted geese that winter in Mexico occur in this region. The Interior Highlands also supports significant numbers of light geese (lesser snow and Ross' geese) and green-winged teal, pintails, shovelers, and Mexican ducks (a rare, nonmigratory mallard subspecies similar to the mottled duck). Interestingly, small numbers of mallards winter in the northern Interior Highlands, forming the southernmost boundary of the species' North American range.
One of the most intensively farmed regions of Mexico, the Interior Highlands has suffered extensive wetland losses in recent decades, as vast areas of marshland have been diked and drained for agriculture and urban expansion. Many other wetlands have been robbed of their water sources for irrigation, human consumption, and power generation or have been severely degraded by overgrazing, pollution, and siltation. In an effort to reverse this trend, DUMAC has joined a coalition of government agencies, conservation organizations, and universities to conserve wetlands in high-priority waterfowl areas of the Interior Highlands. Because much of the land in the region is privately owned, DUMAC works closely with farmers and ranchers to manage watersheds in a sustainable manner that protects and enhances wetlands and water quality. Landowners receive assistance to establish buffer zones surrounding wetlands and streams by constructing cattle-exclusion fences and restoring natural vegetation on adjacent uplands.
DUMAC also is working to inven-tory and map key waterfowl habitats in the Interior Highlands. DU and several partners are nearing completion of an extensive satellite inventory of key Arctic goose wintering habitats in Mexico. This information will be critical to guide future habitat conservation programs, and to develop more comprehensive wintering population surveys of Arctic geese in the Interior Highlands and other key areas of northern Mexico.
The vast and diverse wetland systems bordering Mexico's Gulf Coast and the Yucatan Peninsula rival the Pacific Coast in their importance to waterfowl and other migratory birds. The most important waterfowl wintering area in this region is the Laguna Madre of Tamaulipas, lying just south of the U.S. border. Recent surveys indicate that this estuary supports nearly 1 million wintering ducks, including 35 percent of the continental population of redheads.
Historically, the Laguna Madre was protected from the Gulf by a narrow barrier island. With limited freshwater inflow from the mainland, salinity levels in the lagoon typically ranged from two to three times that of seawater. Few species of vegetation can withstand such conditions, except highly salt-tolerant shoalgrass, which is a favorite food of redheads and other wintering waterfowl in the region. In recent decades, the construction of a series of shipping channels linking the Laguna Madre to the Gulf have altered salinity levels in the estuary, favoring less salt-tolerant sea grass species. These invaders are now rapidly displacing shoalgrass in many areas, which could potentially cause a food shortage for redheads and other wintering waterfowl. DUMAC is presently conducting research that monitors the health of the estuary's shoalgrass beds, as well as wintering waterfowl and shorebird numbers in the region. In addition, DUMAC is leading efforts to secure permanent government protection of the Laguna Madre to prevent future degradation of its fragile ecology.
In addition to the importance of shoalgrass to wintering redheads and other waterfowl, the birds are also dependent upon numerous freshwater ponds found along the coastline. Redheads must fly at least once, and sometimes two or three times, each day to these ponds, where they drink large quantities of water to purge their bodies of high salt loads ingested while feeding on shoalgrass. Many of these freshwater ponds are dependent on rainfall from tropical storms, so their abundance varies greatly from year to year. During dry periods, tens of thousands of redheads and other waterfowl rely upon relatively few wetlands for their survival. As a result, DUMAC is working closely with ranchers along the coastline to protect and restore freshwater wetlands used by large numbers of redheads and other waterfowl.
Farther south, DUMAC is focusing its conservation efforts in several other important wetland systems along the Gulf Coast, including the Tamiahua and Alvarado lagoons, Tabasco wetlands, and Campeche and Yucatan lagoons. These diverse habitats include tidal flats, mangrove swamps, tropical flooded deciduous forests, and freshwater marshes that provide migration and wintering habitat for the majority of the continent's blue-winged teal, as well as great numbers of other neotropical migratory birds. Although large areas of these ecosystems have been granted government protection, many wetlands remain vulnerable to pollution, urban expansion, and industrial development.
DUMAC is working closely with government agencies and other partners to map and classify wetland habitats in high-priority areas of the Gulf Coast and to build support for current and future conservation initiatives. In addition, DUMAC actively restores wetlands that have been degraded by human activity or natural events. For example, on the Isla Arena project in the state of Campeche, DUMAC restored the natural hydrology on 20,000 acres of wetlands used by large numbers of blue-winged teal and other waterbirds. Prior to completion of this project, the construction of a road had effectively impounded this large lagoon, killing mangroves and other vegetation. By placing culverts through the road, DUMAC restored the exchange of freshwater and salt water to and from the Gulf, allowing wetland vegetation once again to flourish throughout the area.
In addition to its many habitat conservation, research, and monitoring programs, DUMAC sponsors training courses for conservation professionals from throughout Mexico and Latin America. To date, DUMAC has trained 190 conservation professionals, who have returned to their home countries as ambassadors for wetlands and waterfowl conservation. By leading efforts to conserve Mexico's wetlands and educating a new generation of conservation leaders, DUMAC is playing an important role in the conservation of North America's waterfowl and many other migratory birds.