In the history of life on our planet, the human species is certainly the one that has posed the greatest threat to other forms of life. The various ways we have altered our environment has been profound in the last 200 years.

In the year 1000, the human population was around 275,000,000. The population hit a billion in 1800 and now exceeds eight billion people. Our population has resulted in great losses in natural habitat. We need to look beyond on our own self-interest and conserve other species. But what are we to do?

One of the simplest actions we can take is to protect existing habitat. Contributing to land trusts and non-governmental organizations as well as maintaining our own property are all helpful. This habitat-based mechanism of conservation considers the communities of organisms collectively. It’s the rising tide raises all boats idea.

However, some species are declining, many due to the direct or indirect effects of human activities. To help those species, we need conservation actions targeted at improving the lot of the declining species. Such actions entail practical and ethical problems.

Consider the mute swan, an invasive species from Europe. With their sinuous necks and large size, these swans are appealing birds. However, they pose significant threats to co-existing native waterfowl by competing for food and destroying aquatic plants. They are aggressive birds and will attack humans. The approach of many wildlife agencies is to kill these invasive birds because of their effect on native birds. That decision seems reasonable to me.

The European starling was introduced into North America in the latter part of the 19th century. These birds have since spread throughout North America with a population of over 200 million. Starlings have a number of impacts including competing with native cavity-nesting birds for nest holes, spreading the seeds of invasive plants and eating and reducing fruit quality of apples, grapes, cherries, strawberries, and peaches. I have little doubt that had starlings been introduced in the past decade, wildlife biologists would have quickly removed them.


The Kirtland’s warbler fell to a population of only 174 males in 1974, but has rebounded in its primary habitat in Michigan after the removal of cowbirds. Vincent Cavalieri/USFWS/TNS

The Kirtland’s warbler, mostly restricted to the jack pine forests in northern Michigan, fell to a population of only 174 males in 1974. Restoration of the species was started with the use of fire to create more suitable jack pine forests and intensive trapping of brown-headed cowbirds. Cowbird females lay eggs in the nests of other species, fooling the parents into raising cowbirds. Cowbird parasitism on Kirtland warbler’s nest was measured at 59% previous to 1971.

Cowbird removal was successful, and Kirtland’s warbler is recovering and spreading its range. But brown-headed cowbirds are native species. The species historically followed bison around in the west but the clearing of land in the east for agriculture created habitat for them to expand their range. Cowbirds only arrived in the Kirtland’s warbler range around 1880.

What is the ethical perspective on this conservation practice? Cowbirds were only in Michigan because of human activities. Do we choose the warbler over the cowbird? Should we have let nature take its course? Should the prevention of an extinction win the day?

The northern spotted owl is a resident of old growth forest in the Pacific Northwest. Its habitat is shrinking due to logging. The closely related barred owl has been expanding westward, aided by human alterations to the habitat. Barred owls outcompete spotted owls, and the U.S. Fish and Wildlife Service recently submitted a proposal to kill 470,000 barred owls over the next 30 years to prevent spotted owl extinction. In addition to practical problems in a project this size, the project also has significant ethical implications.

A recent article in Conservation Biology reviews the practice of killing gulls on offshore islands in the Gulf of Maine to protect nesting terns, whose eggs and chicks are subject to gull predation. The argument has been that gulls have increased unnaturally over the past century in the Gulf of Maine because of human impacts. The argument then is that terns are doing poorly because of the increased gull numbers.

The authors dispute the narrative that gulls are overpopulated in the Gulf of Maine. They argue that gull removal is based on precarious reasoning and may be deterring conservationists from finding more effective ways to improve the plight of terns.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at

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