— Congress passes the original Endangered Species Act. Section 7 says that federal agencies must ensure that any federal action "doesn’t cause destruction or modification of habitat" that is deemed critical for a listed species.
— The Fish and Wildlife Service and the National Marine Fisheries Service publish a notice in the Federal Register explaining that designating critical habitat is "necessary and desirable, whenever and wherever possible."
— The Service designates its first critical habitats, for the snail darter, the yellow-shouldered blackbird, the American crocodile, the California condor, the Indiana bat and the Florida manatee.
— The U.S. Supreme Court halts construction of the Tellico Dam in Tennessee to protect the critical habitat of the endangered snail darter, a three-and-a-half-inch-long fish. (Congress later overturns the ruling by exempting the dam from the ESA.)
— A U.S. district judge stops a smaller dam and a power plant on a Wyoming tributary to the North Platte River to protect critical habitat for the endangered whooping crane.
— In the first formal definition of critical habitat, Congress calls it any part of the landscape — flora, fauna, climate, soil, water and air — containing features "essential to the conservation of a species." But partly in reaction to the snail darter and whooping crane cases, Congress allows the Fish and Wildlife Service to exclude areas if the costs of designation exceed the benefits, or if such designation would cause additional risk to a species.
— The Carter administration lists 41 species to protect against what the president calls "imminent threats" that could destroy their habitat. In the following years, the Fish and Wildlife Service designates critical habitat for dozens of species, including more than a million acres for the gray wolf and 58,680 for the whooping crane.
— Shortly after the election of President Ronald Reagan, the Service, under the control of Interior Secretary James Watt, slows the pace of new listings to a trickle. The average annual number of listings plummets, from 33 between 1976 and 1979 to 9 between 1980 and 1983.
— The Interior Department proposes revisions to the ESA, adopted three years later, that make it much more difficult to prove that critical habitat designation adds protection beyond that provided by the law’s ban on acts that could "jeopardize" a species’ existence.
— The Service issues a memo saying that "only very infrequently has (critical habitat) provided, or had the potential to provide, the margin of difference in the welfare or likelihood of recovery of a species. In contrast, a proposed (habitat protection) very frequently has caused or contributed to public or interagency antagonism, increased the amount of agency work days required to complete a listing action…"
— Service biologist Carl Couret writes that officials of six Service field offices have told him that they believe critical habitat has helped or could help protect a listed species, and in some instances has proven very important.
— Service biologist John Sidle writes a peer-reviewed paper that appears to disparage the benefits of critical habitat. The paper is cited to this day by the rule’s critics, but Sidle says it has been misinterpreted, and that he supports critical habitat for most species.
— The Interior Department’s solicitor’s office determines that critical habitat does provide additional benefits. In a memo to the agency’s regional directors, Fish and Wildlife Service Deputy Director Richard Smith warns that the argument that critical habitat protections are the same as rules prohibiting "jeopardizing" species will not hold up in court.
— Republicans, led by Georgia Rep. Newt Gingrich, take control of Congress for the first time since 1952. Rep. Richard Pombo, R-Calif., leads the charge to roll back environmental laws, including the Endangered Species Act.
— Richard Pombo testifies before a Senate subcommittee that critical habitat for the endangered San Joaquin kit fox stripped the value from his family’s land. But no critical habitat has ever been designated for the fox. Later, on the MacNeil-Lehrer News Hour, Pombo admits he has never been directly affected by critical habitat.
— The "Republican Revolution" crumbles. In the wake of Republican election losses, Gingrich resigns as House speaker and gives up his seat in the House.
— Richard Pombo becomes chairman of the House Resources Committee.
— With George W. Bush president, the Interior Department orders the Fish and Wildlife Service to include a disclaimer in critical habitat designations that reads, in part, "In 30 years of implementing the ESA, the Service has found that the designation of statutory critical habitat provides little additional protection to most listed species, while consuming significant amounts of scarce conservation resources."
— The Center for Biological Diversity files a Freedom of Information Act request seeking documentation backing up the Service’s disclaimer. Twice, the agency replies by saying it "has no documents responsive to your request."
— A decade-old proposal to designate the Lower Colorado River as critical habitat for the endangered razorback sucker and other fish leads Interior Secretary Gale Norton to sign an agreement with the three Lower Basin states protecting 8,100 acres of riparian, marsh and backwater habitat.
— The Center’s science and policy director, Kieran Suckling, and two other scientists write a study, later published in the peer-reviewed journal Biosciences, saying that in the years 1996-1997 and 1999-2000, species with critical habitat did twice as well as species without it.
— Responding to another Center FOIA request, the Service releases an e-mail from an agency official, whose name is redacted, that takes issue with an early draft of the Center’s study. The e-mailer adds, however, "As flawed as the authors’ approach might be, they have more science behind their position than the (Interior Department) and/or the administration has behind theirs."
— Richard Pombo tries, for the 12th time, to get an ESA rewrite through the House of Representatives – and succeeds. If passed by the Senate and approved by the president, the proposal would eliminate the critical habitat rule.
— Senate leaders have promised an ESA reform bill by late February or early March.