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Updated 11 November 2004

Consequences Vol. 3, No. 1, 1997








Editor's Summarry of Articles

The Case Of The Missing Songbirds


Are songbirds as prevalent today as once they were? How are wild birds counted and how well do we really know how many there are? How significant are the declines, and do they apply to all birds, everywhere, or only some of them? What are the reasons for changes in their numbers? Why are some affected more than others? What do we lose when songbirds disappear from fields or forests? What can we do, individually or collectively, to preserve migratory songbird populations?

An Assessment

In the last thirty years many but not all species of migratory songbirds have diminished in numbers in North America, as verified by extensive field surveys that have been conducted, each year, during the summer breeding season. Particularly affected are certain forest-dwelling birds and many that breed in meadows and grasslands, but the patterns of change are complex, and the populations of some that thrive in areas of human disturbance have increased. For most migratory songbirds the declines can be attributed to our more intensive use of the land, including changes in farming and forestry and other human development that perturbs their summer breeding ground. The songbirds that each year cross the Gulf of Mexico to spend their winters in more tropical climates are pinched at both ends due to extensive deforestation and other land-use changes in Central and South America. Migrant flocks have also been deprived of vital stopover places by the changes we make in coastal areas, where nearly half of the U.S. population now lives. In some of these cases the breeding habitat of certain songbirds is destroyed altogether, as when forests are cleared or wetlands reclaimed. More often, the more probable cause is the systematic replacement of larger and more continuous forests or meadows by a patchwork of fragmented parcels that are no longer large enough to serve as source areas for fledgling birds. Other causes are more subtle, as when through our own development of the land we give advantage to certain species at the expense of others -- some of which, like cowbirds, jays, and some mammals like raccoons, are the natural enemies of species in decline.


There are several good reasons why we should be concerned about the plight of songbirds. For the many people who watch birds as a hobby, the joy of seeing and hearing them is probably cause enough. But they are of considerable economic value as consumers of insects, particularly those that defoliate trees, and to tourism in areas where birds concentrate. They play a major role in the health and functioning of natural ecosystems by eating insects, dispersing seeds, and pollinating flowers. Since they attract so much interest, they also serve as a visible index of global environmental change. All life is now impacted by ever-increasing human pressures. Steps to protect and conserve songbirds on their breeding, migratory, and wintering grounds are beneficial for most of the other living organisms that share the same habitat, including people.

Go to: The Case of the Missing Songbirds

Do We Still Need Nature?
The Importance of Biological Diversity


In what ways do we still rely on the natural world? What attributes of Nature, in the face of mounting human numbers, are most important for our needs? How fast are plants and animals disappearing today, compared to what would happen were we not here? Which species are the most important to us, or to the way the world works, and need we be concerned with all of them? What is behind today's loss of biodiversity, and what can be done to stem the tide? What is the economic value of biodiversity and what is lost when it declines?

An Assessment

To allow resilience in the face of natural changes, and to function at all, Nature relies very much on a certain diversity of living things, their individual genetic make-up, and the ecosystems in which they live. Our own activities, over the years, have systematically reduced this essential feature of the natural world, to the point where today native plants and animals are disappearing at at least 50 to 100 times the background rate. The pace of loss in some parts of the world is projected to reach rates that will equal, or perhaps exceed, the times of mass extinction in the geologic past. The problem goes beyond extinctions to include marked reductions in populations of many species, for the role that classes of organisms play in ecosystems depends not only on what they do but on how many there are to do it. The causes of decline are more obvious than the cures, and include the extensive use of the land for human purposes, as through expanded agriculture and silviculture and the draining of wetlands; the tendency of human development to break up parcels of natural land cover into smaller and more isolated segments; over- exploitation of nature and natural resources; the introduction of alien species; pollution and toxification of land and water; and climate change.


The costs of allowing biodiversity to decline so precipitously are very real, and can be counted in economic terms in units of the natural resources that depend on biodiversity and that provide food and wood and recreation for almost everyone. Plants taken from the wild are the source of one in five of the top prescription drugs and will continue to serve as the source of the new pharmaceuticals of the future. A more extensive but less direct set of benefits is derived from the services that ecosystems provide, including the improvement of quality of streams and underground water and the reduction of flooding. But the greatest and most disturbing loss when species disappear is the permanent depletion of as-yet untapped genetic resources for the future, which we have only begun to use in pharmacy and agriculture and genetic engineering. The pool of resources hidden in the genetic make-up of living things, whatever they are, is huge, and when they disappear they are lost forever, not only to us but for all who come after.

Go to: Do We Still Need Nature? The Importance of Biodiversity

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