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Where have all the Songbirds gone? Where Have All The Songbirds Gone? Every June, some 2200 amateur ornithologists and bird watchers across the United States and Canada join in an annual bird count called the Breeding Bird Survey. Organized in 1966 by the U.S. Fish and Wildlife Service to follow bird population changes, this survey has discovered some shocking trends. While birds such as robins, starlings, and blackbirds that prosper around humans have increased their number and distribution over the past thirty years, many of our most colorful and melodious forest birds have declined severely. The greatest decreases have been among the true songbirds such as thrushes, orioles, tanagers, catbirds, vireos, buntings, and warblers. These long-distance migrants nest in northern forests but spend the winters in South or Central America or in the Caribbean Islands. Scientists call them neotropical migrants. In many areas of the eastern United States and Canada, three-quarters or more of the neotropical migrants have declined significantly since the survey was started. Some that once were common have become locally extinct. Grover Archbold Park and Rock Creek Park in Washington, DC, for instance, lost 75 percent of their songbird population and 90 percent of their long-distance migrant species in just twenty years. Nationwide, cerulean warblers, American redstarts, and ovenbirds declined about 50 percent in the single decade of the 1970s. Studies of radar images from National Weather Service stations in Texas and Louisiana suggest that only about half as many birds fly across the Gulf of Mexico each spring now compared to the 1960s. This could mean a loss of about half a billion birds in total. What causes these devastating losses? Destruction of critical winter habitat is clearly a major issue. Birds often are much more densely crowded in the limited areas available to them during the winter than they are on their summer range. Unfortunately, forests throughout Latin America are being felled at an appalling rate. Central America, for instance, is losing about 1.4 million hectares (2 percent of its forests or an area about the size of Yellowstone National Park) each year. If this trend continues, there will be essentially no intact forest left in much of the region in fifty years. But loss of tropical forests is not the only threat. Recent studies show that fragmentation of breeding habitat and nesting failures in the United States and Canada may be just as big a problem for woodland songbirds. Many of the most threatened species are adapted to deep woods and need an area of 10 hectares (24.7 acres) or more per pair to breed and raise their young. As our woodlands are broken up by roads, housing developments, and shopping centers, it becomes more and more difficult for these highly specialized birds to find enough contiguous woods to nest successfully. Predation and nest parasitism also present a growing threat to many bird species. While birds have probably always lost eggs and nestlings to predators, there has been a startling increase in predation in the past thirty years. Raccoons, opossums, crows, bluejays, squirrels, and house cats thrive in human-dominated landscapes. They are protected from larger predators like wolves or owls and find abundant supplies of food and places to hide. Their numbers have increased dramatically, as have their raids on bird nests. A comparison of predation rates in the Great Smoky Mountain National Park and in small rural and suburban woodlands shows how devastating predators can be. In a 1000-hectare study area of mature, unbroken forest in the national park, only one songbird nest in fifty was raided by predators. By contrast, in plots of 10 hectares or less near cities, up to 90 percent of the nests were raided. Nest parasitism by brown-headed cowbirds is one of the worst threats for woodland songbirds. Originally called buffalo birds, these small blackbirds were adapted to follow migratory bison herds picking up seeds and insects from the droppings. Because they didn't stay in one place long enough to raise a family, they developed the habit of depositing their eggs in the nests of other species, leaving their young to be raised by surrogate parents. The young cowbirds are generally larger and more aggressive than the resident chicks, which generally starve to death because they don't get enough food. Adult cowbirds also find a welcome source of food and shelter around humans. Once fairly uncommon in the United States, there are now about 150 million of these parasites. A study in southern Wisconsin found that 80 percent of the nests of woodland species were raided by predators and that three-quarters of those that survived were invaded by cowbirds. Another study in the Shawnee National Forest in southern Illinois found that 80 percent of the scarlet tanager nests contained cowbird eggs and that 90 percent of the wood thrush nests were taken over by these parasites. The sobering conclusion of this latter study is that there probably is no longer any place in Illinois where scarlet tanagers and wood thrushes can breed successfully. What can we do about this situation? First, we can support sustainable development in Third World countries so that people there can enjoy a better standard of living without destroying their forests and natural areas. A number of such projects are discussed elsewhere in this book. Next, we should identify and protect critical habitat at home and abroad on which especially endangered species depend. Buying up inholdings that fragment the forest and preserving corridors that tie together important areas will help. In areas where people already live, we could encourage clustering of houses to protect as much woods as possible. We also might discourage clearing underbrush and trees from yards and parks to leave shelter for the birds. Could we reduce the number of predators or limit their access to critical breeding areas? Human residents might not like the idea of reintroducing wolves and bears, but they might accept fencing or trapping of small predators. A campaign to keep house cats inside during the breeding season would certainly help. Ethical Considerations Some wildlife managers already are trapping cowbirds. The Kirtland's warbler is one of the rarest songbirds in the United States. It nests only in young, fire-maintained jackpine forests in Michigan. Controlled burning to maintain habitat for this endangered species was started in the 1960s, but the population continued to decline. Studies showed that 90 percent of the nests were being parasitized by cowbirds. Since 1972, refuge managers have trapped and killed some 7000 cowbirds each year to protect the warblers. In the past two decades, the number of breeding pairs of warblers has risen from about 150 to nearly 400. Would it be possible to do something similar on a nationwide scale? Could we trap and kill 150 million cowbirds? Should we eliminate one species to save another? What do you think? Cerro Grande Fire Forces Evacuation May, 2000 Los Alamos, New Mexico
During May 2000, New Mexico's largest recorded forest fire raged just west of Los Alamos. Fed by winds of 25 miles per hour, with gusts of up to 50 miles per hour, the Cerro Grande fire forced the evacuation of Los Alamos and came close to threatening storage facilities containing radioactive materials. The fire was controversial because it began as a normal prescribed burn, intentionally set by the National Park Service in nearby Bandelier National Monument. When it got out of hand, fingers were quickly pointed at the park service for planning that led to the loss of more than 200 homes. Prescribed burns have become a common and important part of land management in many environments. The idea behind prescribed burns in forests is that frequent small fires cause little damage to forests, are beneficial to forest ecosystems, and prevent the buildup of fuel (dead wood) that would support larger, catastrophic fires. Prescribed burns should be started only when weather conditions are safe---that is, under moderately humid conditions with little wind. During the burn, fire crews contain the fire by lighting backfires (smaller fires that eliminate fuel in a band ahead of the main fire) and by clearing firebreaks (openings across which the fire should not be able to spread). May's Cerro Grande fire began as an effort to clear fuel in Bandelier. Unfortunately, weather conditions turned dry and windy after the fire was started on May 4, and instead of burning out, the fire jumped its planned boundaries. By May 16, shortly before the fire finally ended, more than 46,000 acres had burned, and 1,200 people were working---on the ground and in planning offices---to minimize the damage. Interior Secretary Bruce Babbit declared a 30-day moratorium on prescribed burns in all western states and ordered an investigation into what went wrong at Cerro Grande. This report was released May 18. It concluded, among other things, that the fire plans had not adequately considered fuel conditions outside the planned fire boundary or taken into account 3-5-day wind forecasts. However, the general prescribed burn policy was considered sound, and prescribed fires---with careful planning---will continue to be an important part of public land management (see related article). To learn more, see these related websites: Cerro Grande Prescribed Fire Investigation Report President declares disaster area in Los Alamos Southwest Area's Wildland Fire Operations Website Prescribed fires: info from the U.S. Forest Service To read more, see: Environmental Science, A Global Concern, Cunningham and Saigo, 6th ed. Environmental Science, A Study of Interrelationships, Enger and Smith, 7th
ed. May, 2000 s Boundary Waters Canoe Area Wilderness, Minnesota
Catastrophic wildfires were feared during the summer of 2000 in the Boundary Waters Canoe Area Wilderness (BWCAW) in Minnesota. One year previously, on July 4, 1999, a sudden windstorm toppled trees on thousands of acres of forest in this corner of northern Minnesota adjacent to the Canadian border. The area of damage is an irregular swath of downed and broken trees 4 to 12 miles wide and 30 miles (50 km) long, running in a southwest-northeast direction across the wilderness area. The BWCAW is the most popular wilderness area in the United States. More than 200,000 visitors come there to canoe and camp every year. Forest Service officials say a serious fire is inevitable following the blowdown. The only questions are when the fire will happen and how long-lasting the damage will be. The worst type of fire would be a "plume-dominated" fire---one with updrafts reaching 30,000 feet (10,000 m) or more, causing strong winds that further feed the fire, fire whirls along the edge of the fire, and spot fires jumping 3 miles (5 km) to start additional fires. Whether this type of fire develops is a matter of weather conditions. A hot, dry, and windy summer could produce conditions that would support this type of fire. A cool, wet summer would reduce the chances of an extremely large fire. In anticipation of fire, the Forest Service gathered and rented fire-fighting equipment, including airplanes and helicopters, and hired extra fire-fighting staff for the summer. Also, some prescribed fires were planned to reduce fuel near key road corridors and residential areas, but as of early June 2000, weather conditions had not allowed any prescribed fires to be carried out. Some fires occur every summer in the Boundary Waters area. In a normal year, 57% of the fires are caused by lightning strikes, while 43% are started by campers who fail to fully extinguish their campfires. Historically, this region is a fire-adapted ecosystem, having some tree species that reproduce readily only after a fire. However, after more than half a century of fire suppression there, a dangerous level of fuel has accumulated on the ground, and human habitation has seriously encroached on the wilderness. Now the most serious concerns are not for the forests and wildlife but for the property of the people who live on the edge of the wilderness as well as for campers who may be in the area when a fire occurs. To learn more, see these related websites: Blowdown info from the Superior National Forest Mn DNR damage assessment page, with interactive image viewer Report on the blowdown, summer 1999 Fuel assessment report, February 2000 To read more, see: Environmental Science, A Global Concern, Cunningham and Saigo, 6th ed. Environmental Science, A Study of Interrelationships, Enger and Smith, 7th
ed. Case Study: Restoration of the Bermuda Cahow The cahow is a seabird endemic (restricted) to Bermuda and adjacent islands off the east coast of North America. A member of the petrel family, related to albatrosses, shearwaters, and other wide-ranging seabirds, cahows once formed dense, noisy colonies that fed on the rich fisheries around the island. When European sailors first landed on Bermuda 400 years ago, cahows were abundant. Like many endemic island species, the ground-nesting cahow had never experienced predation and had no defenses against the pigs, goats, and rats introduced by the first settlers. Overhunting and habitat destruction further decimated the species. By the late 1600s-about the same time that the last dodo was killed on Mauritius-cahows disappeared from Bermuda. For three centuries, the cahow was assumed to be extinct. In 1951, though, scientists found a few living cahows on some tiny islands in the Bermuda harbor. A protection and recovery program was begun immediately, including establishment of a sanctuary on the 6-hectare (15-acre) Nonsuch Island, which has become an excellent example of environmental restoration. Nonsuch was a near desert after centuries of abuse, neglect, and habitat destruction. All the native flora and fauna were gone, along with most of its soil. This was a case of re-creating nature rather than merely protecting what was left. Sanctuary superintendent David Wingate, who has devoted his entire professional life to this project, has brought about a remarkable transformation of this barren little island. Reestablishing a viable population of cahows has had the added benefit of rebuilding an entire biological community. The first step in restoration was to reintroduce native vegetation and re-create habitat. Thousands of native tree and shrub seedlings were planted. Initial progress was slow as trees struggled to get a foothold; once the forest knit itself into a dense thicket that deflected the salt spray and ocean winds, however, the natural community began to reestablish itself. It takes constant surveillance to remove volunteer exotic plant species and to exclude rats, cats, and toxic toads that swim from the main island. The benefits of indigenous species became apparent in 1987 when Hurricane Emily roared across Bermuda. Up to 70 percent of nonnative trees were uprooted or snapped off by gale-force winds, littering streets and bringing down power lines. The dense, low-profile, native trees on Nonsuch were barely touched by the winds. Demands soared for hurricane-adapted species to replace those lost along streets and in gardens. Just providing habitat for the cahows was not enough, however, to restore the population. Each pair lays only one egg per year and only about half survive under ideal conditions. It takes eight to ten years for fledglings to mature, giving the species a low reproductive potential. They also compete poorly against the more common long-tailed tropic birds that steal nesting sites and destroy cahow eggs and fledglings. Special underground burrows were built with baffled entrances designed to admit only cahows. Young birds were hand-raised by humans to ensure a proper diet and protection. By 1997, the cahow population had rebounded to fifty-six nesting pairs. It is too early to know if this is enough to be stable over the long term, but the progress to date is encouraging. Perhaps more important than rebuilding this single species is that the island has become a living museum of precolonial Bermuda that benefits many species besides its most famous resident. It is a heartening example of what can be done with vision, patience, and some hard work. If you go into your local pet store, chances are, you'll see some cichlids (Haplochromis sp.) for sale. These small colorful, prolific fish come in a wide variety of colors and shapes from many parts of the world. The greatest cichlid diversity on earth - and probably the greatest vertebrate diversity anywhere - are found in the three great African rift lakes: Victoria, Malawi, and Tanganyika. Together, these lakes once had about 1,000 types of cichlids - more than all the fish species in Europe and North America combined. All these cichlids apparently evolved from a few ancestral varieties in the 15,000 years or so since the lakes formed, one of the fastest and most extensive examples of vertebrate speciation known. Unfortunately, a well-meaning but disastrous fish stocking experiment has wiped out at least half the cichlid species in these lakes in the last twenty years and set off a series of changes that is upsetting important ecological relationships. Lake Victoria, which lies between Kenya, Tanzania, and Uganda, has been particularly hard hit. Cichlids once made up 80 percent of the animal biomass in the lake and were the base for a thriving local fishery, supplying much-needed protein for native people. Colonial administrators, however, regarded the little, bony cichlids as "trash fish" and in the 1960s introduced the Nile perch (Lates niloticus), a voracious, exotic predator that can weigh 100 km (220 lbs) and grow up to 2 m long. The perch gobbled up the cichlids so quickly that by 1980 two-thirds of the haplochromine species in the lake were extinct. Although there still are lots of fish in the lake, 80 percent of the animal biomass is now made up of perch, which are too large and powerful for the small boats, papyrus nets, and woven baskets traditionally used to harvest cichlids. International fishing companies now use large power boats and nylon nets to harvest great schools of perch, which are filleted, frozen, and shipped to markets in Europe and the Middle East. Because the perch are oily, local fishers can't sun dry them as they once did the cichlids. Instead, the perch carcasses discarded by processing factories are cooked or smoked over wood fires for local consumption. Forests are being denuded for firewood, and protein malnutrition is common in a region that exports 200,00 tons of fish each year. Perhaps worst of all, Lake Victoria, which covers an area the size of Switzerland, is dying. Algae blooms clog the surface, oxygen levels have fallen alarmingly, and thick layers of soft silt are filling in shallow bays. Untreated sewage, chemical pollution, and farm runoff are the immediate causes of this eutrophication, but destabilization of the natural community is ultimately responsible. The swarms of cichlids that once ate algae and rotting detritus were the lake's self-cleaning system. Eliminating them threatens the long-term ability of the lake to support any useful aquatic life. As this example shows, biological diversity is important. Misguided management and development schemes that destroyed native species in Lake Victoria resulted in an ecosystem that no longer supports the natural community or the native people dependent on it. Until about twenty-five years ago, the Black Sea supported a diverse and productive ecosystem with five times as many fish per square kilometer as the adjacent Mediterranean. Black Sea commercial fishing provided an important food source for neighboring countries, while popular beaches and seaside resorts made Crimea the Russian equivalent of south Florida. In recent years, however, the Black Sea has experienced severe pollution problems that illustrate the potential for catastrophic collapse of some ecosystems. Eutrophication and toxification have caused fisheries to fail abruptly. Untreated sewage washing up on beaches has forced closure of many resort areas. Massive fish kills and algal blooms have turned many sheltered bays into stinking cesspools that no one wants to go near. Reckless energy development, unrestrained industrial expansion, and rapidly growing human populations in the watersheds surrounding the sea lie at the roots of these environmental problems. Every year millions of tons of sediment and pollutants - including untreated sewage, industrial wastes, oil, heavy metals, and radioactive substances - flow into the Black Sea. The Danube River, for instance, carries chrome copper, mercury, lead, zinc, and oil to the Black Sea at twenty times the levels that the Rhine River transports those contaminants to the North Sea. One city - Bratislava, the capital of Slovakia - dumps 73 million cubic meters of industrial and municipal wastes every year into the Danube. Since 1970, the Danube's nitrate and phosphate loads have increased sixfold and fourfold, respectively. Levels of these same chemicals in the Dniester River, which originates in Ukraine and Moldavia, are up 700 percent over this same period. Tanker dumping and production spills cause higher oil pollution levels in the Black Sea than in the busy Persian Gulf. Less than one percent of Turkey's population is served by any kind of sewage treatment. Fed by the Danube and more than thirty other rivers from Eastern Europe and Western Asia, but landlocked except for a narrow outlet through the Bosporus and Dardanelles to the Mediterranean, the Black Sea's unique hydrology adds to pollution woes. The top 100 meters of the sea are less salty than most oceans, but are nutrient rich and well oxygenated. Beneath this upper layer is a deep, essentially lifeless zone of cold, highly saline water with little oxygen and high levels of poisonous hydrogen sulfide. These density differences, which have existed for centuries, prevent mixing between layers. Pollutants entering the sea are trapped in the shallow surface layer and quickly reach toxic concentrations. In 1986, fish catches in the Black Sea amounted to 900,000 metric tons, but by 1992, less than one-tenth of this amount was caught. Overfishing may be partly to blame for this catastrophic decline, but toxic pollutants and oxygen depletion have killed many species that once flourished in the sea. Another problem is invasion by an exotic jellyfish-like ctenophore Mnemiopis leidya from the East Coast of North America. With no natural enemies, this predator - which feeds on zooplankton, fish eggs, and larvae - has undergone explosive population growth. During some times of the year, these comb jellies make up more than 95 percent of all biomass in the Black Sea. Is there any hope in this dismal situation? Perhaps. In 1992, in spite of fierce religious, racial, political, and economic divisions, Bulgarians, Georgians, Rumanians, Russians, Turks, Armenians, and Ukrainians met in Bucharest to hammer out a draft convention to protect the Black Sea. Following precedents set by international conventions for other regional seas, this agreement will focus on preventing land-based pollution, vessel dumping, and deposition of atmospheric contaminants. Watershed protection is especially important, and the eight Central European countries in the Danube drainage basin have developed a separate understanding to clean up this historic river. Few of the states around the Black Sea have the institutional capacity, manpower, or funds to do much at present. It may take decades before any tangible improvements will be seen. Still, if agreements for environmental protection can be reached in this deeply divided region, perhaps there is hope for other places as well. |
