A Letter from Biologists to the United States Senate Concerning Science in the Endangered Species Act

Published Jul 14, 2008

Update: Biologists organized a similar letter in April of 2009, urging the Obama administration to restore the scientific foundation of the Endangered Species Act

The Letter from Biologists to the U.S. Senate Concerning Science in the Endangered Species Act was a tremendous success and demonstrates the importance of science and scientists to protect species and their habitats. Over 5,700 scientists with biological expertise signed their name to the letter, with at least 26 from every state and over 900 institutions. This is an extraordinary response from the scientific community given that the letter was open for signatures for just over one month. The 5,738 signers include:

  • At least 26 signers from every state, many with a few hundred
  • Over 900 institutions represented
  • 39 National Academy of Science members
  • 12 MacArthur Genius Award recipients
  • 6 National Medal of Science recipients
  • 2 Crafoord Prize recipients


The sign-on letter concept originated in discussions among a small group of scientists, who agreed on the main concepts and drafted the letter text. The letter was then widely circulated to biologists around the country. The Union of Concerned Scientists played a coordinating role in collecting signatures and producing the letter for the Senate in collaboration with Earthjustice and the National Wildlife Federation. The initial scientists included: David Bain, University of Washington; C. Ronald Carroll, University of Georgia; Melissa Grigione, University of South Florida; Lynn Maguire, Duke University; Dennis Murphy, University of Nevada, Reno; Bruce Pavlik, Mills College; and Stuart Pimm, Duke University.


The scientists behind the letter established the criteria to ensure the scientific credibility of the letter. The letter was open to biologists with or working towards an advanced degree, which included both masters and doctoral candidates and medical professionals, as they have a particular understanding of biology and human health. In addition, on a case-by-case basis, individuals who do not have an advanced degree but who have extensive life experience working in the field that gives them particular knowledge of species and their habitats were included. Signers had the option to sign without an affiliation.

January 2006

Dear Senators:

We are writing as biologists with expertise in a variety of scientific disciplines that concern biological diversity and the loss of species. With the Senate considering policies that could have long-lasting impacts on this nation's species diversity, we ask that you take into account scientific principles that are crucial to species conservation. Biological diversity provides food, fiber, medicines, clean water, and myriad other ecosystem products and services on which we depend every day. If we look only at well-studied species groups, nearly one-third of native species in the United States are at risk of disappearing.¹  Extinction is truly irreversible - once gone, individual species and all of the services that they provide us cannot be brought back.

On December 8, 1973, President Richard Nixon signed the Endangered Species Act ("ESA") with the goal of conserving endangered and threatened species and the ecosystems on which they depend. For species that have been listed and provided protection under the ESA, much of that purpose has been achieved. According to an article in the September 30, 2005, edition of Science, less than one percent of listed species have gone extinct since 1973, while 10 percent of candidate species still waiting to be listed have suffered that fate. In addition to the hundreds of species that the Act has protected from extinction, listing has contributed to population increases or the stabilization of populations for at least 35 percent of listed species, and perhaps significantly more, as well as the recovery of such signature species as the peregrine falcon. While complete recovery has been realized for just two percent of species listed, given the precarious state of most species when listed, this represents significant progress. 

One of the great strengths of the Endangered Species Act is its foundation in sound scientific principles and its reliance on the best available science.² Unfortunately, recent legislative proposals would critically weaken this foundation. For species conservation to continue, it is imperative both that the scientific principles embodied in the Act are maintained, and that the Act is strengthened, fully implemented, and adequately funded.  


Objective scientific information and methods should be used in listing species, subspecies, and distinct population segments as endangered or threatened under the Act. While non-scientific factors may appropriately be considered at points later in the process of protecting species, their use in listing decisions is inconsistent with biologically defensible principles. Due to the fragile state of many of those species that require the Act's protections, the listing process needs to proceed as promptly as possible; otherwise, species will go extinct while waiting to be listed.


Habitat provides the unique food, shelter, and other complex requirements that each species needs for its survival; habitat loss and degradation are the principal reasons for the decline of most species at risk. Habitat protection is essential if species are to be conserved and the goals of the ESA are to be met. The relationship between species, their habitats, and the threats they face can be exceedingly complex. Therefore, the chances of species recovery are maximized when habitat protection is based on sound scientific principles, and when the determinations of the biological needs of at-risk species are scientifically well informed.

The obligation for federal agencies to consult with the appropriate wildlife agency and its biologists when federal actions could affect habitat for listed species is an indispensable provision in the ESA. It provides the means for science to inform decisions about the habitat-dependent survival and recovery of species at-risk. The designation of critical habitat places further obligations on the Federal government to, among other things, protect the habitat essential to species recovery. It is far more effective, far easier, and far less expensive to protect functioning natural habitats than it is to recreate them once they are gone.

Scientific tools

The current Endangered Species Act standard of "best available science" has worked well and has been flexible enough over time to accommodate evolving scientific information and practice. Failure to keep the ESA open to the use of scientific information from the best available research and monitoring, and to rely on impartial scientific experts, will contribute to delays in species recovery and to species declines and extinctions. Critical scientific information should not only include current empirical data, but also, for example, historic habitat and population information, population surveys, habitat and population modeling, and taxonomic and genetic studies. Use of scientific knowledge should not be hampered by administrative requirements that overburden or slow the Act's implementation, or by limiting consideration of certain types of scientific information. 

Recovery plans

Recovery plans must be science-based documents that are developed with the input of scientists and are responsive to new information. Recovery plans must be based on the best possible information about the specific biology of each species, must identify threats to each species and address what is needed to mitigate those threats, and must predict how species are likely to respond to mitigation measures that may be adopted. To be most effective, recovery plans need to incorporate scientific principles of adaptive management, so they can be updated as new information on species and their habitats becomes available. Changes to the ESA that would delay completion of recovery plans, or provide for inflexible recovery goals that cannot be informed by new or additional scientific knowledge, should be avoided.

Scientific advances and new issues

The scientific community has contributed significant new information on imperiled species, their uses of habitats, and threats to those resources since the ESA was first passed into law. Serious, new, and as yet insufficiently addressed issues, such as global warming and invasive species, have emerged as primary environmental concerns that affect the fate of our native species diversity. We urge Congress to initiate thorough studies to consider the foremost problems that drive species toward extinction. 

Losing species means losing the potential to solve some of humanity's most intractable problems, including hunger and disease. The Endangered Species Act is more than just a law - it is the ultimate safety net in our life support system. As Earth has changed and as science has progressed since the Endangered Species Act was authorized in 1973, the ESA has served our nation well, largely because of its flexibility and its solid foundation in science. It is crucial to maintain these fundamental principles. The challenges of effective implementation of the Act should not be interpreted to require substantive rewriting of this valuable, well-functioning piece of legislation.

Thank you very much for taking our concerns into account. We are available to discuss any and all of the issues we have raised.



Selected signers

(Full list of signers is in the document PDF)

David Bain, University of Washington, Friday Harbor, WA

Ron Carroll, University of Georgia, Atlanta, GA

Paul Ehrlich, Stanford University, Stanford, CA

Thomas Eisner, Cornell University, Ithaca, NY

Melissa Grigione, Ph.D., University of South Florida, Tampa, FL

Jane Lubchenco, Oregon State University, Corvallis, OR

Lynn Maguire, Duke University, Durham, NC

Gary Meffe,University of Florida,Gainesville, FL

Judy Meyer, University of Georgia, Athens, GA

Harold Mooney, Stanford University, Stanford, CA

Dennis Murphy, University of Nevada, Reno, NV

Barry Noon, Colorado State University, Ft. Collins, CO

Stuart Pimm, Duke University, Durham, NC

Gordon Orians, University of Washington, Seattle, WA

Peter Raven, Missouri Botanical Garden, St. Louis, MO

Michael Soule, University of California, Santa Cruz, Santa Cruz, CA

John Terborgh, Duke University, Durham, NC

¹From NatureServe, an international network of scientists cataloguing biological diversity.

²The National Academy of Science’s National Research Council said in its seminal 1995 report, Science and the Endangered Species Act: "…there has been a good match between science and the ESA…[and] the ESA is based on sound scientific principles."

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