In the last quarter century, nature has often reminded us that the fates of wildlife and our own species are intertwined

As celebration of the first Earth Day took place across the country in April 1970, brown pelican eggs on Anacapa Island off the coast of Ventura, California, were breaking under the weight of incubating adults. For four months, the birds laid eggs in a total of 552 nests without producing any young. Finally, in July, a single chick hatched on the island, the species' only regular nesting ground in the state. The cause of the eggshell thinning: DDT poisoning.

Of course, Anacapa's brown pelicans were not the only animals harmed by DDT; nor were they the only pelican population in serious trouble. But for a nation waking up to the idea that the fates of wildlife and our own species are intertwined, the island's one chick 25 years ago delivered a notably poignant message. And in that respect, the young bird was not alone. For every so often, the natural world delivers to our own species lessons that we comprehend particularly well--lessons that are in many cases taught more quietly by other animals and plants.

In honor of the 25th anniversary of Earth Day, the following list chronicles 25 of the most resonant messages this country has received from wildlife during the last quarter century. It is no accident that many are from birds; ever since the proverbial coal miners' canaries, birds have been our most telling harbingers of news from and about nature.

BROWN PELICANS

DDT poisons birds: Only a decade before a single brown pelican chick hatched on Anacapa in 1970, the species' young may have numbered in the thousands on the California island. But 25 years ago, DDT came close to wiping out the colony. The widespread pesticide and related chemicals had also long been poisoning brown pelicans in southeastern states--as well as ospreys, bald eagles, cormorants and many other species all over the country. By 1972, the EPA had banned the use and manufacture of DDT, not only for the sake of wildlife, but also because it was a suspected human carcinogen. That possibility was made all the more alarming by the knowledge--detailed by biologist Rachel Carson a decade earlier in her landmark book Silent Spring--that DDT had become ubiquitous, even showing up in human milk. The Environmental Protection Agency (EPA) now lists DDT, which has diminished in the environment but is still widely present, as a probable human carcinogen.

WHALES

Taking action can work: The supply of whales and the uses for their meat, oil and other parts once seemed endless. But by 1972, despite some protections, many species were nearly extinct-- including the massive blue whale, the "singing" humpback and the right whale. That year, the United States declared eight whale species endangered and passed the Marine Mammal Protection Act to protect whales and dolphins in U.S. waters. But many countries kept whaling. Of course, whales were hardly the first hunted animals to convey by their very absence the need for a chance to recuperate. Bison, pronghorn and cougars, just to name a few, were in serious trouble until they were protected. But in the case of whales, the message was arguably heard the loudest of all, and "Save the Whales" became a rallying cry. In 1982, the International Whaling Commission finally agreed to a moratorium that started in 1986. Though not absolute, the uneasy truce has helped many whale species survive and even show some signs of recovery.

LAKE TROUT

Humans can ingest potent doses of poisons passed up the food chain: Though the United States and Canada joined forces in 1972 on a long-range cleanup of the Great Lakes, hundreds of pollutants (some wind-borne from around the world) still contaminate the region. Many wildlife species are now doing much better than they were 23 years ago. But because of the way toxics accumulate in the food chain, they become concentrated in fish. Many of the lakes' fish-eating birds and mammals still have abnormal reproductive problems. In 1970, Michigan issued the first fish-eating advisory for people. Today, every Great Lakes state warns of human health risks from eating the region's fish-- particularly lake trout and carp. Similar warnings have been posted for fish from many other U.S. waters.

FIDDLER CRABS

Oil spills can have long-term, sublethal effects: In the 1970s, scientists at a number of research institutions started reporting results from studies of a 1969 oil spill in West Falmouth, Massachusetts. Researchers still refer to that work, important because the spill was real (not in a laboratory), impartial (not funded by industry) and thorough. In 1977, one study revealed that fiddler crabs were still suffering physiological and behavioral damage from the oil. Most striking, the oil was impairing their ability to dig burrows critical to their survival. The oil's persistence and its sublethal effects in the marsh prefigured the ongoing damage in Alaska from the 1989 Exxon Valdez oil spill--even though the two ecosystems radically differ. Oiled mussel beds are still fouled more than five years later. And some mussel predators in the area--including young sea otters and many species of sea ducks--are suffering population problems that may be related to ingested oil.

SONGBIRDS

Migrating creatures are vulnerable at both ends of their routes: Neotropical migrant songbirds were first hit by toxic pesticides, herbicides and farm chemicals (all of which are now far more restricted by U.S. legislation than in the middle of this century). Then the birds were stressed by the ongoing fragmentation of North American forests, which has left less and less deep-woods habitat, and by continued cattle grazing of critical streamside habitat in the arid West. In the early 1980s, at the other end of migration routes, the destruction of tropical forests in Central and South America for crops and cattle grazing took off in a big way--and songbirds lost out again. The birds' travels and diverse habitat requirements make recovery efforts difficult, though many species respond quickly to improved habitat.

BROOK TROUT

Pollution from far away can create disasters in pristine places: When anglers in New York's Adirondack mountains started coming away empty handed in the 1970s from many of the lakes, the threat of acid rain hit home. Many of the lakes had no signs of any sport fish. Though not the most sensitive species, the prized brook trout was the most widely missed. Scientists suspected the cause was wind-borne sulfur and nitrogen from Midwestern industrial activity. In 1986, scientists found acid rain to be a key factor in the Adirondacks' fish decline. By 1990, when Clean Air Act revisions required sulfur dioxide reductions, thousands of U.S. lakes were highly acidic. Though acid rain is still a factor in accelerated tree deaths in eastern forests, the strengthened regulations have helped cut some of the pollution, and some lakes are showing signs of recovery. In the Adirondacks, if lake chemistry continues to improve, biologists may restock brook trout in some lakes. Last August, federal industry allowances for sulfur dioxide emissions were further reduced.

MALLARDS

Lead shot is poisonous: If there ever was any question about what lead does to birds that mistake shot pellets for food or grit, one only had to look at what lead exposure does to humans: brain damage, behavioral problems and even death (see page 32). That ingested lead kills waterfowl was first established in 1919. By the early 1970s, lead shot in wetland bottoms was killing up to three million birds a year, including bald eagles that preyed on poisoned ducks. Of all the birds affected, probably mallards have been the most missed--in part because of their relative lack of shyness around people and their comparatively large numbers. In 1985, pressured by a petition from the National Wildlife Federation, the U.S. Fish and Wildlife Service completed a plan to phase out the use of lead shot for shooting ducks, geese, swans and coots. Long delayed, the plan finally went into effect in 1991, a move widely credited to pressure from NWF lawsuits. Today, birds are still dying from ingesting shot that has accumulated in their habitat over the years.

Lead sinkers used for fishing are also proving to be a threat and are unexpectedly killing loons, which are not bottom feeders. The birds may ingest sinkers in fish prey or with gravel for grinding food. The EPA recently proposed banning lead sinkers nationwide.

HONEYCREEPERS

Introduced species can wreak havoc and weaken biodiversity: With few mammal predators, the wildlife on Hawaii's islands--the most isolated in the world--evolved nearly defenseless. Then Polynesian and European settlers introduced animals and plants that have destroyed habitat and easily devoured whole populations of species. Of the islands' 128 native nesting birds alone, half are now extinct.

In the mid-1970s, the Hawaiian Forest Bird Survey started counting native birds and gave force to habitat restoration efforts. Among the findings: only 24 species of honeycreepers-- tiny, nectar-seeking birds--survive, down from 65. As with much of the islands' wildlife, alien species plague the birds in a number of ways. Predators such as cats, roof rats and mongooses have discovered that nestling honeycreepers jump to the ground when frightened (their only predators were once hawks or owls attacking from above). In a more subtle chain of perils, mosquitoes carry alien diseases to the birds. The insects breed in water-filled holes excavated in tree fern trunks by feral, alien pigs as they feed (and destroy forest). Alien species beleaguer more robust ecosystems too. A few examples from the contiguous 48 states: The kudzu vine has overgrown parts of the South. The European starling is now the country's most populous bird. And in just a few years, Mediterranean zebra mussels have clogged water-intake pipes from Canada through the Great Lakes and southward.

FURBISH LOUSEWORT

The most specialized organisms can be the most vulnerable: What's in a name? In the case of the endangered Furbish lousewort, a moment of fame in the late 1970s. For without its odd moniker, this perennial herb with the yellow flowers would surely not have become well known outside of Maine, where its existence helped stall plans for dams (eventually canceled for economic reasons) in the late 1970s and early 1980s.

Along with the fame came a lesson in evolution and adaptation. The plant grows on north-facing banks of the St. John River, in well-drained, calcium-rich, sandy soil. It does best with little competing vegetation, which the river's big spring runoff helps control. The lousewort is arguably the most successful organism to exploit those particular conditions. Change them, and you lose the plant--which means losing biological diversity. As recent studies of Midwestern prairie habitat have helped confirm, such diversity is critical for ecosystem survival: When conditions change, an ecosystem with a variety of organisms available to exploit new niches will do best.

CARIBOU

Calving and oil development don't mix: Caribou were little more than a distraction in the mid-1970s for oil companies that had to modify the Trans Alaska Pipeline so the Central Arctic herd could cross it. But when developers eyed the Arctic National Wildlife Refuge, the species became a barricade.

While occasional caribou--mostly bulls--wander near Prudhoe Bay's oilfield and the pipeline, biologists warned that the Porcupine herd that migrates to Alaska's northeast edge would be seriously harmed by gas or oil work and structures. The term "core calving ground" acquired political significance, and caribou have been a major factor in a series of federal decisions to protect the area. The message from the 170,000-strong herd also stands for a fragile web of life that includes musk-oxen, rich offshore marine life and 135 bird species--including vast numbers of migrant waterfowl. The oil industry continues to try to pry open the refuge.

BACTERIA

The tiniest wildlife can hold the keys to understanding human health: In 1978, scientists found that bacteria in Yellowstone National Park's hot springs contain enzymes that enable replication of the bacteria's hereditary machinery at high temperatures. For molecular biologists in search of a way to synthesize DNA fragments, the discovery was big news. Today, those same enzymes are key to the polymerase chain reaction, which replicates DNA fragments. Among its many uses, the technique is central to biomedical research, including studies of the genetics of disease.

DUSKY SEASIDE SPARROW

The Endangered Species Act can't work unless it is enforced: By 1980, the last five dusky seaside sparrows, all males, were captured in Florida. The plight of the white-breasted songbird with the patch of yellow on its dark wings captured the public imagination. In 1987, news of the death of the last one, named Orange Band, made many obituary columns. Denizen of salt marshes on and near an island, the sparrow coexisted with a voracious mosquito population, which humans fought with pesticides and eradication of marshes. When the Kennedy Space Center and a development boom ate up more marsh, the bird was in serious trouble--and the required protection of its habitat under the Endangered Species Act of 1973 came too little, too late. The last female dusky seaside sparrow was seen in 1977.

HIV

Humans are still prey: In 1982, scientists gave a name to a baffling disease that had reached epidemic proportions: acquired- immune-deficiency syndrome. In 1984, they identified its cause: human immunodeficiency virus. To a generation that thought of cancer as the last terrible human disease to be conquered, HIV is a reminder that we are still prey, particularly for the smallest wildlife. Not only are new diseases a very real threat, but many known scourges have developed drug-resistant strains.

STONEFLIES

Never assume that seemingly useless habitat is unimportant: In the last decade, scientists have identified whole ecosystems thriving in places long overlooked. One such region is the world deep within river beds and floodplains, called the hyporheic zone. There, researchers have found scores of shrimp, worm, bacteria, algae and insect species, many never seen before. Interacting with the river ecosystem, they support a food chain reaching all the way to humans. One study of the zone under Montana's Flathead River in 1984 found immature stoneflies in ground water 1.5 miles from the river, which means that pollution or deep digging, even at that distance, could affect the river's health. How so? Stoneflies are the hyporheic zone's top predators--and as adults above ground, they congregate at the river and are important fish food. Other newly appreciated ecosystems include the forest canopy (threatened marbled murrelets, for example, nest in Northwest treetops), the ocean floor (where sunless hot-water vents in places like the Gulf of Mexico feature abundant life) and the deep subsurface of the Earth (where microorganisms thrive in soil as far down as 9,481 feet.

NORTHERN PINTAILS

Even tiny wetlands are critical habitat: Only a few decades ago, annual wet seasons created millions of ponds across the Midwest. In these "potholes," great migrations of waterfowl bred. But in the last 30 years, as farmland development and drainage projects eliminated many potholes, duck populations declined dramatically- -also bringing attention to the parallel plight of species such as piping plovers, black terns and Franklin's gulls. A decade- long drought starting in 1981 pointed up just how important the small wetlands can be; waterfowl declined by 40 percent. In the mid and late 1980s, a number of federal protections for wetlands went into effect, including required review of all proposed wetlands activities, the Conservation Reserve Program for farmland, the North American Waterfowl Management Plan and the EPA's policy of no net loss of wetlands. Today, thanks to those actions and the efforts of private groups--along with a wet year- -duck populations are at their highest levels in more than a decade. Still, numbers of northern pintails, one of the 10 major species of ducks, haven't yet recovered.

SEA OTTERS

Oil transportation is terribly flawed: Though oil had been carelessly carried and spilled the world over long before the 1989 Exxon Valdez disaster in Alaska's Prince William Sound, images of the region's oil-slicked and dying sea otters made the point like never before. The past six years have seen some new regulation, including the U.S. Oil Pollution Act of 1990. But as continuing spills and their wildlife victims make clear, oil still is not moved safely. Around the world, aging tankers and lax regulations comprise disasters waiting to happen. The problem exists on land too. In this country, a recent audit of the Trans Alaska Pipeline found 4,920 management, operational and technical problems. In Russia, a ruptured pipeline last October poured untold amounts of oil into a fragile Arctic ecosystem.

FROGS

Amphibians may be an early warning system for global environmental problems: Realizing that many species of frogs, toads and salamanders were mysteriously dwindling, scientists from 63 countries compared notes in 1989. They found a worldwide pattern that may have begun as early as 20 years earlier. Among the experts' guesses for the declines: pesticides, industrial chemicals, habitat loss, agricultural chemicals or the thinning ozone layer. Frogs may be uniquely sensitive to all of the above, since they live in both water and air, and they easily absorb substances through their skin. Many frogs, which have survived on Earth for 200 million years, are suffering from weakened immune systems. Populations of bats have also declined drastically worldwide, perhaps for similar reasons.

SPOTTED OWLS

An animal in trouble is a habitat in trouble: This ages-old lesson had never caused so much controversy. In 1990, the Northwest's spotted owl was listed as a threatened species, and the headlines that followed declared a hard choice: jobs or owls. The truth was that the trees were becoming scarce, and timber jobs had already been declining. Still, the publicity pointed up the critical role a barometer species such as the spotted owl can play in identifying a whole ecosystem at risk. That last lesson made such an impression at the federal level that it helped generate a new way of thinking about species conservation dubbed "ecosystem management."

PACIFIC YEW

The natural world is a rich pharmacy: In 1991, a substance in Pacific yew bark was found to shrink some cancer tumors. But the tree was widely reported to be scarce or endangered, and no one knew its population. Loggers had long considered yews to be trash vegetation in old-growth forests: Had clearcutting razed a cure for cancer?

As it turns out, yews are plentiful, and researchers have also created synthetic taxol. As for the drug, it is not a cure, but it has kept its promise. Taxol shrinks tumors in some patients for months at a time. Though yew bark got the attention, its lesson can be found in an array of other wildlife, including leeches (they release a powerful anticoagulant), frogs (their skin holds antibiotics and painkillers) and the rosy periwinkle (source of an anti-cancer substance).

SALT CEDAR

Weakened ecosystems invite invaders: The introduction of hearty Eurasian tamarisk (commonly known as salt cedar) and Russian olive to help halt erosion and serve as ornamentation in parts of the arid West seemed like a good idea in the 19th and early 20th centuries. But in recent decades, the trees have almost obliterated native ecosystems along some rivers in the Southwest- -mostly where flood control has dried up floodplains, weakening native plants such as cottonwoods. Invaders need not be alien species. One recent study by U.S. and British ecologists found that fragmentation of a bur oak savanna in Minnesota led to replacement of the oaks by native weed species. Once the uniquely adapted oak ecosystem was weakened, it could no longer hold its ground against the more common invaders, and biological diversity lost out.

SONG SPARROWS

Overgrazed riparian ecosystems can recover if given a chance: Three years after the Bureau of Land Management established a 15- year grazing moratorium on Arizona's San Pedro River in 1988, the number of song sparrows in every 100 acres increased from less than one to 61. Along the 40-mile section of river, other neotropical migrants also dramatically rebounded, most notably common yellowthroats and yellow-breasted chats. The exceptionally thorough study was hopeful news for the cattle-damaged West, where streamside areas support 75 percent of the wildlife. Without cattle chomping new growth to the ground, young cottonwood and willow trees, grasses, sedges and reeds all flourished. The birds found new understory vegetation below existing older trees for feeding, resting and escaping predators. The birds' recoveries mirrored the rallying health of many other animals and plants. Even the river has changed: New growth has stabilized the banks, and the channel is becoming narrower and deeper, which has also improved the habitat for fish.

WADING BIRDS

Altering waterways can have a big price: Dwindling populations of South Florida's egrets, herons, wood storks and other wading birds have been eloquently making the point for decades that canals and drainage systems are drying up the region's famed river of grass. Last year, Florida instituted a $685 million clean-up plan, and Congress nearly doubled federal funding for Everglades and Florida Bay restoration efforts from $28.5 million to $46.6 million. All of that, say field biologists, will only help start long-term recovery. South Florida's wading birds are not alone in delivering this message. Last year, the dire plight of Pacific salmon, due largely to dams on the Northwest's waterways, reached crisis proportions. And in California's Central Valley, which holds the largest irrigation system in the Western Hemisphere, wildlife including migrant waterfowl and fish suffered greatly during recent drought years.

WILLOWS

Plants not only actively defend themselves, some actually warn other plants: In 1982, plant physiologists were amazed to learn that tent-caterpillar-infested willows not only change their leaf chemistry to repel the invaders, they somehow send a warning to other nearby willows to do the same. Soon after, sugar maples were found to also signal each other. Reports had been piling up for about a decade of various plants that respond to insect assaults with bursts of toxic substances in leaves and stems. But actual plant communication had been unheard of. Then, in 1992, came the announcement that tomato seedlings send electrical signals to their leaves that warn of insect chomping. The signals prompt the plant's noninfested leaves to make chemicals that bugs find difficult to digest.

All of these phenomena hold great promise for new weapons in the nonpesticide arsenal against agricultural pests. Today, researchers are experimenting with "vaccines" that provoke plants' defenses.

BALD EAGLE

Without our laws and regulations, U.S. biodiversity would be far weaker: Last year, the U.S. Fish and Wildlife Service proposed shifting the bald eagle from the federal category of endangered (in most of the 48 contiguous states) to the less dire listing of threatened. The bald eagle promises to join the alligator, the whooping crane, the greenback cutthroat trout and many other U.S. species that would likely be extinct if not for a safety net of environmental regulation--including the banning of DDT, protection of habitat and the phaseout of lead shot. For direct protection of wildlife, of course, the most relevant legislation is the Endangered Species Act: One recent federal study found that nearly 40 percent of the species protected by the act are now stable or recovering. Even so, the act and its implementation are far from perfect. Hundreds of listed U.S. species likely still face extinction, and many hundreds more in trouble haven't yet made the list.

PEREGRINE FALCONS

Toxic chemicals persist in the environment for decades: After the 1972 ban on DDT in this country, brown pelicans made impressive comebacks--as did ospreys, peregrine falcons, bald eagles and many other species. Today, pelican chicks again hatch in the thousands on Anacapa Island. DDT, however, is not gone from our environment. This country still has enough long-deposited DDT (used to control crop-eating insects during the 1950s and 1960s) to poison wildlife in some areas. And many other countries still use DDT and other toxic chemicals that the atmosphere deposits widely around the globe. Not only that, scientists now understand that DDT is one of a group of related chemicals that can have similar effects. In the West, certain peregrine falcon populations have reproductive problems that may be due to DDT or other toxics. One news report last July told of a researcher using surgical gloves to avoid contact with a peregrine's toxic- laden eggshells. That detail starkly made the point that the same chemicals implicated in the birds' reproductive difficulties also may harm humans (for the latest on that concern, see page 38). As for brown pelicans--threatened now by other pollution and commercial fishing of their food supply--they are now telling us the work of saving them is not yet done.

Lisa Drew is a National Wildlife senior editor. Research assistant Laura Hutman and librarian Sharon Levy helped report and research this article.