Where have all the Songbirds gone?
Prescribed fires in Mexico
Fires in the Boundary Waters Canoe Wilderness web
Bermuda Cahow
Lake Victoria Perch
Black Sea
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  <![CDATA[<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::femafire::/sites/dl/free/0072452706/22962/femafire.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif">femafire (9.0K)</a>]]>femafire
Firefighters survey damage after the Cerro Grande fire. (Image source: FEMA.)
|
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 Fire in the national
parks 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.
Fire in environmental restoration, pp. 118-19
Fire management and fire policy in national parks, p. 319 Environmental Science, A Study of Interrelationships, Enger and Smith, 7th
ed.
Restoring ecosystems, p. 88 Major Fires Expected in Popular Wilderness Area May, 2000 s Boundary Waters Canoe Area Wilderness, Minnesota  <![CDATA[<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::blowdown::/sites/dl/free/0072452706/22962/blowdown.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif">blowdown (47.0K)</a>]]>blowdown Broken and fallen trees are ripe for a major fire in the Boundary Waters
Canoe Area Wilderness. (Image source: Minnesota Department of Natural
Resources.) |
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 Mn DNR blowdown photo pages
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.
Fires and ecosystem resilience, pp. 226-27
Fire management, p. 319
Wilderness areas, pp. 342-44 Environmental Science, A Study of Interrelationships, Enger and Smith, 7th
ed.
Restoring ecosystems, p. 88 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. Killing Lake Victoria 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. Black Sea in Crisis 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. |
2002 McGraw-Hill Higher Education