Bird

VIII

Birds and Humans

Birds have been of ecological and economic importance to humans for thousands of years. Archaeological sites reveal that prehistoric people used many kinds of birds for food, ornamentation, and other cultural purposes. The earliest domesticated bird was probably the domestic fowl or chicken, derived from jungle fowls of Southeast Asia. Domesticated chickens existed even before 3000 bc. Other long-domesticated birds are ducks, geese, turkeys, guinea-fowl, and pigeons.

Today the adults, young, and eggs of both wild and domesticated birds provide humans with food. People in many parts of Asia even eat nests that certain swiftlets in southeastern Asia construct out of saliva. Birds give us companionship as pets, assume religious significance in many cultures, and, in the case of hawks and falcons, perform work for us as hunters. People in maritime cultures have learned to monitor seabird flocks to find fish, sometimes even using cormorants to do the fishing.

Birds are good indicators of the quality of our environment. In the 19th century, coal miners brought caged canaries with them into the mines, knowing that if the birds stopped singing, dangerous mine gases had escaped into the air and poisoned them. Birds provided a comparable warning to humans in the early 1960s, when the numbers of peregrine falcons in the United Kingdom and raptors in the United States suddenly declined. This decline proved to be caused by organochlorine pesticides, such as DDT, which were accumulating in the birds and causing them to produce eggs with overly fragile shells. This decline in the bird populations alerted humans to the possibility that pesticides can harm people as well. Today certain species of birds are considered to be indicators of the environmental health of their habitats. An example of an indicator bird is the northern spotted owl, which can only reproduce within old growth forests in the Pacific Northwest.

Many people enjoy bird-watching. Equipped with binoculars and field guides, they identify birds and their songs, often keeping lists of the various species they have witnessed. Scientists who study birds are known as ornithologists. These experts investigate the anatomy, behavior, evolutionary history, ecology, classification, and species distribution of both domesticated and wild birds.

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A

Birds as Menaces

In general, birds pose little direct danger to humans. A few birds, such as the cassowaries of New Guinea and northeastern Australia, are capable of killing humans with their strong legs and bladelike claws, but actual attacks are extremely rare. Many birds become quite aggressive when defending a nest site; humans are routinely attacked, and occasionally killed, by hawks engaging in such defense. Birds pose a greater threat to human health as carriers of diseases. Diseases carried by birds that can affect humans include influenza and psittacosis.

Negative impacts by birds on humans are primarily economic. Blackbirds, starlings, sparrows, weavers, crows, parrots, and other birds may seriously deplete crops of fruit and grain. Similarly, fish-eating birds, such as cormorants and herons, may adversely impact aquacultural production. However, the economic benefits of wild birds to humans are well documented. Many birds help humans, especially farmers, by eating insects, weeds, slugs, and rodents.

B

Endangered Birds

Although birds, with some exceptions, are tremendously beneficial to humans, humans have a long history of causing harm to birds. Studies of bone deposits on some Pacific islands, including New Zealand and Polynesia, suggest that early humans hunted many hundreds of bird species to extinction. Island birds have always been particularly susceptible to predation by humans. Because these birds have largely evolved in the absence of land-based predators, they are tame and in many cases flightless. They are therefore easy prey for humans and the animals that accompany them, such as rats. The dodo, a flightless pigeonlike bird on the island of Mauritius in the Indian Ocean, was hunted to extinction by humans in the 1600s.

With colonial expansion and the technological advances of the 18th and 19th centuries, humans hunted birds on an unprecedented scale. This time period witnessed the extinction of the great auk, a large flightless seabird of the North Atlantic Ocean that was easily killed by sailors for food and oil. The Carolina parakeet also became extinct in this time period, although the last one of these birds survived in the Cincinnati Zoo until 1918.

In the 20th century, a time of explosive growth in human populations, the major threats to birds have been the destruction and modification of their habitats. The relentless clearing of hardwood forests outweighed even relentless hunting as the cause of the extinction of the famous passenger pigeon, whose eastern North American populations may have once numbered in the billions. The fragmentation of habitats into small parcels is also harmful to birds, because it increases their vulnerability to predators and parasites.

Habitat fragmentation and reduction particularly affects songbirds that breed in North America in the summer and migrate to Mexico, the Caribbean, Central America, and Colombia for the winter. In North America, these birds suffer from forest fragmentation caused by the construction of roads, housing developments, and shopping malls. In the southern part of their range, songbirds are losing traditional nesting sites as tropical forests are destroyed and shade trees are removed from coffee plantations.

Pesticides, pollution, and other poisons also threaten today’s birds. These substances may kill birds outright, limit their ability to reproduce, or diminish their food supplies. Oil spills have killed thousands of aquatic birds, because birds with oil-drenched feathers cannot fly, float, or stay warm. Acid rain, caused by chemical reactions between airborne pollutants and water and oxygen present in the atmosphere, has decreased the food supply of many birds that feed on fish or other aquatic life in polluted lakes. Many birds are thought to be harmed by selenium, mercury, and other toxic elements present in agricultural runoff and in drainage from mines and power plants. For example, loons in the state of Maine may be in danger due to mercury that drifts into the state from unregulated coal-fired power plants in the Midwest and other sources. Global warming, an increase in the earth’s temperature due to a buildup of greenhouse gases, is another potential threat to birds.

Many laws have been enacted to protect birds. More than 120 countries signed the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which went into effect in 1975. This treaty regulates or restricts the trade of endangered birds, including many parrots. Treaties between the United States, Canada, and Mexico protect all migratory birds native to North America. In the United States, the Endangered Species Act promotes species and habitat protection.

Other means of protecting birds include the creation of sanctuaries and captive breeding programs. Sanctuaries for birds exist all over the world—two examples are the Bharatpur Bird Sanctuary in India’s Keoladeo National Park, which protects painted storks, gray herons, and many other bird species; and the National Wildlife Refuge system of the United States. In North America, some endangered birds are bred in settings such as zoos and specialized animal clinics and later released into the wild. Such breeding programs have added significantly to the numbers of whooping cranes, peregrine falcons, and California condors. Many countries, including Costa Rica, are finding they can reap economic benefits, including the promotion of tourism, by protecting the habitats of birds and other wildlife.

The protection of the earth’s birds will require more than a single strategy. Many endangered birds need a combination of legal protections, habitat management, and control of predators and competitors. Ultimately, humans must decide that the bird’s world is worth preserving along with our own.

Scientific classification: All birds belong to the class Aves, which is subdivided into 27 orders.

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