515 U.S. 687 (1995)

BABBITT, SECRETARY OF INTERIOR, et al.
v.
SWEET HOME CHAPTER OF COMMUNITIES FOR A GREAT OREGON et al.

No. 94-859.

United States Supreme Court.

Argued April 17, 1995. Decided June 29, 1995. CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE DISTRICT OF COLUMBIA CIRCUIT

*689 Stevens, J., delivered the opinion of the Court, in which O'Connor, Kennedy, Souter, Ginsburg, and Breyer, JJ., joined. O'Connor, J., filed a concurring opinion, post, p. 708. Scalia, J., filed a dissenting opinion, in which Rehnquist, C. J., and Thomas, J., joined, post, p. 714.

Deputy Solicitor General Kneedler argued the cause for petitioners. With him on the briefs were Solicitor General Days, Assistant Attorney General Schiffer, Beth S. Brinkmann, Martin W. Matzen, Ellen J. Durkee, and Jean E. Williams.

*689 John A. Macleod argued the cause for respondents. With him on the brief were Steven P. Quarles, Clifton S. Elgarten, Thomas R. Lundquist, and William R. Murray.^[*]

*690 Justice Stevens delivered the opinion of the Court.

The Endangered Species Act of 1973 (ESA or Act), 87 Stat. 884, 16 U. S. C. § 1531 (1988 ed. and Supp. V), contains a variety of protections designed to save from extinction species that the Secretary of the Interior designates as endangered or threatened. Section 9of the Act makes it unlawful for any person to "take" any endangered or threatened species. The Secretary has promulgated a regulation that defines the statute's prohibition on takings to include "significant habitat modification or degradation where it actually kills or injures wildlife." This case presents the question whether the Secretary exceeded his authority under the Act by promulgating that regulation.

I

Section 9(a)(1) of the Act provides the following protection for endangered species:^[1]

"Except as provided in sections 1535(g)(2) and 1539 of this title, with respect to any endangered species of fish or wildlife listed pursuant to section 1533 of this title it is unlawful for any person subject to the jurisdiction of the United States to—. . . . .

*691 "(B) take any such species within the United States or the territorial sea of the United States." 16 U. S. C. § 1538(a)(1).

Section 3(19)of the Act defines the statutory term "take":

"The term `take' means to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct." 16 U. S. C. § 1532(19).

The Act does not further define the terms it uses to define "take." The Interior Department regulations that implement the statute, however, define the statutory term "harm":

"Harm in the definition of `take' in the Act means an act which actually kills or injures wildlife. Such act may include significant habitat modification or degradation where it actually kills or injures wildlife by significantly impairing essential behavioral patterns, including breeding, feeding, or sheltering." 50 CFR § 17.3 (1994).

This regulation has been in place since 1975.^[2]

A limitation on the § 9 "take" prohibition appears in § 10(a)(1)(B) of the Act, which Congress added by amendment in 1982. That section authorizes the Secretary to grant a permit for any taking otherwise prohibited by § 9(a)(1)(B) "if such taking is incidental to, and not the purpose of,the carrying out of an otherwise lawful activity." 16 U. S. C. § 1539(a)(1)(B).

In addition to the prohibition on takings, the Act provides several other protections for endangered species. Section 4, 16 U. S. C. § 1533, commands the Secretary to identify species of fish or wildlife that are in danger of extinction and to publish from time to time lists of all species he determines to *692 be endangered or threatened. Section 5, 16 U. S. C. § 1534, authorizes the Secretary, in cooperation with the States, see § 1535, to acquire land to aid in preserving such species. Section 7 requires federal agencies to ensure that none of their activities,including the granting of licenses and permits, will jeopardize the continued existence of endangered species "or result in the destruction or adverse modification of habitat of such species which is determined by the Secretary . . . to be critical."16 U. S. C. § 1536(a)(2).

Respondents in this action are small landowners, logging companies, and families dependent on the forest products industries in the Pacific Northwest and in the Southeast, and organizations that represent their interests. They brought this declaratory judgment action against petitioners, the Secretary of the Interior and the Director of the Fish and Wildlife Service, in the United States District Court for the District of Columbia to challenge the statutory validity of the Secretary's regulation defining "harm," particularly the inclusion of habitat modification and degradation in the definition.^[3] Respondents challenged the regulation on its face. Their complaint alleged that application of the "harm" regulation to the red-cockaded woodpecker, an endangered species,^[4] and the northern spotted owl, a threatened species,^[5] had injured them economically. App. 17-23.

*693 Respondents advanced three arguments to support their submission that Congress did not intend the word "take" in § 9 to include habitat modification, as the Secretary's "harm" regulation provides. First, they correctly noted that language in the Senate's original version of the ESA would have defined "take" to include "destruction, modification, or curtailment of [the] habitat or range" of fish or wildlife,^[6] but the Senate deleted that language from the bill before enacting it. Second, respondents argued that Congress intended the Act's express authorization for the Federal Government to buy private land in order to prevent habitat degradation in § 5 to be the exclusive check against habitat modification on private property. Third, because the Senate added the term "harm" to the definition of "take" in a floor amendment without debate, respondents argued that the court should not interpret the term so expansively as to include habitat modification.

The District Court considered and rejected each of respondents' arguments, finding "that Congress intended an expansive interpretation of the word `take,' an interpretation that encompasses habitat modification." 806 F. Supp. 279, 285 (1992). The court noted that in 1982, when Congress was aware of a judicial decision that had applied the Secretary's regulation, see Palila v. Hawaii Dept. of Land and Natural Resources, 639 F. 2d 495 (CA9 1981) (Palila I), it amended the Act without using the opportunity to change the definition of "take." 806 F. Supp., at 284. The court stated that, even had it found the ESA "`silent or ambiguous' " as to the authority for the Secretary's definition of "harm," it would nevertheless have upheld the regulation as a reasonable interpretation of the statute. Id., at 285 (quoting *694 Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837, 843 (1984)). The District Court therefore entered summary judgment for petitioners and dismissed respondents' complaint.

A divided panel of the Court of Appeals initially affirmed the judgment of the District Court. 1 F. 3d 1 (CADC 1993). After granting a petition for rehearing, however, the panel reversed. 17 F. 3d 1463 (CADC 1994). Although acknowledging that "[t]he potential breadth of the word `harm' is indisputable," id., at 1464, the majority concluded that the immediate statutory context in which "harm" appeared counseled against a broad reading; like the other words in the definition of "take," the word "harm" should be read as applying only to "the perpetrator's direct application of force against the animal taken . . . . The forbidden acts fit, in ordinary language, the basic model `A hit B.' " Id., at 1465. The majority based its reasoning on a canon of statutory construction called noscitur a sociis, which holds that a word is known by the company it keeps. See Neal v. Clark, 95 U. S. 704, 708-709 (1878).

The majority claimed support for its construction from a decision of the Ninth Circuit that narrowly construed the word "harass" in the Marine Mammal Protection Act of 1972, 16 U. S. C. § 1372(a)(2)(A), see United States v. Hayashi, 5 F. 3d 1278, 1282 (1993); from the legislative history of the ESA;^[7] from its view that Congress must not have intended the purportedly broad curtailment of private property rights that the Secretary's interpretation permitted; and from the ESA's land acquisition provision in § 5 and restriction on federal agencies' activities regarding habitat in § 7, both of which the court saw as evidence that Congress had not intended the § 9 "take" prohibition to reach habitat modification. *695 Most prominently, the court performed a lengthy analysis of the 1982 amendment to § 10 that provided for "incidental take permits" and concluded that the amendment did not change the meaning of the term "take" as defined in the 1973 statute.^[8]

Chief Judge Mikva, who had announced the panel's original decision, dissented. See 17 F. 3d, at 1473. In his view, a proper application of Chevron indicated that the Secretary had reasonably defined "harm," because respondents had failed to show that Congress unambiguously manifested its intent to exclude habitat modification from the ambit of "take." Chief Judge Mikva found the majority's reliance on noscitur a sociis inappropriate in light of the statutory language and unnecessary in light of the strong support in the legislative history for the Secretary's interpretation. He did not find the 1982 "incidental take permit" amendment alone sufficient to vindicate the Secretary's definition of "harm," but he believed the amendment provided additional support for that definition because it reflected Congress' view in 1982 that the definition was reasonable.

The Court of Appeals' decision created a square conflict with a 1988 decision of the Ninth Circuit that had upheld the Secretary's definition of "harm." See Palila v. Hawaii Dept. of Land and Natural Resources, 852 F. 2d 1106 (1988) (Palila II). The Court of Appeals neither cited nor distinguished Palila II, despite the stark contrast between the Ninth Circuit's holding and its own. We granted certiorari to resolve the conflict. 513 U. S. 1072 (1995). Our consideration of the text and structure of the Act, its legislative history, and the significance of the 1982 amendment persuades us that the Court of Appeals' judgment should be reversed.

*696 II

Because this case was decided on motions for summary judgment, we may appropriately make certain factual assumptions in order to frame the legal issue. First, we assume respondents have no desire to harm either the redcockaded woodpecker or the spotted owl; they merely wish to continue logging activities that would be entirely proper if not prohibited by the ESA. On the other hand, we must assume, arguendo, that those activities will have the effect, even though unintended, of detrimentally changing the natural habitat of both listed species and that, as a consequence, members of those species will be killed or injured. Under respondents' view of the law, the Secretary's only means of forestalling that grave result—even when the actor knows it is certain to occur^[9]—is to use his § 5 authority to purchase *697 the lands on which the survival of the species depends. The Secretary, on the other hand, submits that the § 9 prohibition on takings, which Congress defined to include "harm," places on respondents a duty to avoid harm that habitat alteration will cause the birds unless respondents first obtain a permit pursuant to § 10.

The text of the Act provides three reasons for concluding that the Secretary's interpretation is reasonable. First, an ordinary understanding of the word "harm" supports it. The dictionary definition of the verb form of "harm" is "to cause hurt or damage to: injure." Webster's Third New International Dictionary 1034 (1966). In the context of the ESA, that definition naturally encompasses habitat modification that results in actual injury or death to members of an endangered or threatened species.

Respondents argue that the Secretary should have limited the purview of "harm" to direct applications of force against protected species, but the dictionary definition does not include the word "directly" or suggest in any way that only direct or willful action that leads to injury constitutes "harm."^[10] Moreover, unless the statutory term "harm" encompasses *698 indirect as well as direct injuries, the word has no meaning that does not duplicate the meaning of other words that § 3 uses to define "take." A reluctance to treat statutory terms as surplusage supports the reasonableness of the Secretary's interpretation. See, e. g., Mackey v. Lanier Collection Agency & Service, Inc., 486 U. S. 825, 837, and n. 11 (1988).^[11]

Second, the broad purpose of the ESA supports the Secretary's decision to extend protection against activities that cause the precise harms Congress enacted the statute to avoid. In TVA v. Hill, 437 U. S. 153 (1978), we described the Act as "the most comprehensive legislation for the preservation of endangered species ever enacted by any nation." Id., at 180. Whereas predecessor statutes enacted in 1966 and 1969 had not contained any sweeping prohibition against the taking of endangered species except on federal lands, see id., at 175, the 1973 Act applied to all land in the United States and to the Nation's territorial seas. As stated in § 2 of the Act, among its central purposes is "to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved . . . ." 16 U. S. C. § 1531(b).

*699 In Hill, we construed § 7 as precluding the completion of the Tellico Dam because of its predicted impact on the survival of the snail darter. See 437 U. S., at 193. Both our holding and the language in our opinion stressed the importance of the statutory policy. "The plain intent of Congress in enacting this statute," we recognized, "was to halt and reverse the trend toward species extinction, whatever the cost. This is reflected not only in the stated policies of the Act, but in literally every section of the statute." Id., at 184. Although the § 9 "take" prohibition was not at issue in Hill, we took note of that prohibition, placing particular emphasis on the Secretary's inclusion of habitat modification in his definition of "harm."^[12] In light of that provision for habitat protection, we could "not understand how TVA intends to operate Tellico Dam without `harming' the snail darter." Id., at 184, n. 30. Congress' intent to provide comprehensive protection for endangered and threatened species supports the permissibility of the Secretary's "harm" regulation.

Respondents advance strong arguments that activities that cause minimal or unforeseeable harm will not violate the Act as construed in the "harm" regulation. Respondents, however, present a facial challenge to the regulation. Cf. Anderson v. Edwards, 514 U. S. 143, 155-156, n. 6 (1995); INS v. National Center for Immigrants' Rights, Inc., 502 U. S. 183, 188 (1991). Thus, they ask us to invalidate the Secretary's understanding of "harm" in every circumstance, even when an actor knows that an activity, such as draining a *700 pond, would actually result in the extinction of a listed species by destroying its habitat. Given Congress' clear expression of the ESA's broad purpose to protect endangered and threatened wildlife, the Secretary's definition of "harm" is reasonable.^[13]

Third, the fact that Congress in 1982 authorized the Secretary to issue permits for takings that § 9(a)(1)(B) would otherwise prohibit, "if such taking is incidental to, and not the purpose of, the carrying out of an otherwise lawful activity," 16 U. S. C. § 1539(a)(1)(B), strongly suggests that Congress understood § 9(a)(1)(B) to prohibit indirect as well as deliberate takings. Cf. NLRB v. Bell Aerospace Co., 416 U. S. 267, 274-275 (1974). The permit process requires the applicant to prepare a "conservation plan" that specifies how he intends to "minimize and mitigate" the "impact" of his activity on endangered and threatened species, 16 U. S. C. § 1539(a)(2)(A), making clear that Congress had in mind foreseeable rather than merely accidental effects on listed species.^[14] No one could seriously request an "incidental" take *701 permit to avert § 9 liability for direct, deliberate action against a member of an endangered or threatened species, but respondents would read "harm" so narrowly that the permit procedure would have little more than that absurd purpose. "When Congress acts to amend a statute, we presume it intends its amendment to have real and substantial effect." Stone v. INS, 514 U. S. 386, 397 (1995). Congress' addition of the § 10 permit provision supports the Secretary's conclusion that activities not intended to harm an endangered species, such as habitat modification, may constitute unlawful takings under the ESA unless the Secretary permits them.

The Court of Appeals made three errors in asserting that "harm" must refer to a direct application of force because the words around it do.^[15] First, the court's premise was flawed. Several of the words that accompany "harm" in the § 3 definition of "take," especially "harass," "pursue," "wound," and "kill," refer to actions or effects that do not require direct applications of force. Second, to the extent the court read a requirement of intent or purpose into the words used to define "take," it ignored § 11's express provision that a "knowin[g]" *702 action is enough to violate the Act. Third, the court employed noscitur a sociis to give "harm" essentially the same function as other words in the definition, thereby denying it independent meaning. The canon, to the contrary, counsels that a word "gathers meaning from the words around it." Jarecki v. G. D. Searle & Co., 367 U. S. 303, 307 (1961). The statutory context of "harm" suggests that Congress meant that term to serve a particular function in the ESA, consistent with, but distinct from, the functions of the other verbs used to define "take." The Secretary's interpretation of "harm" to include indirectly injuring endangered animals through habitat modification permissibly interprets "harm" to have "a character of its own not to be submerged by its association." Russell Motor Car Co. v. United States, 261 U. S. 514, 519 (1923).^[16]

Nor does the Act's inclusion of the § 5 land acquisition authority and the § 7 directive to federal agencies to avoid destruction or adverse modification of critical habitat alter our conclusion. Respondents' argument that the Government lacks any incentive to purchase land under § 5 when it can simply prohibit takings under § 9 ignores the practical considerations that attend enforcement of the ESA. Purchasing habitat lands may well cost the Government less in many circumstances than pursuing civil or criminal penalties. In addition, the § 5 procedure allows for protection of habitat before the seller's activity has harmed any endangered animal, *703 whereas the Government cannot enforce the § 9 prohibition until an animal has actually been killed or injured. The Secretary may also find the § 5 authority useful for preventing modification of land that is not yet but may in the future become habitat for an endangered or threatened species. The § 7 directive applies only to the Federal Government, whereas the § 9 prohibition applies to "any person." Section 7 imposes a broad, affirmative duty to avoid adverse habitat modifications that § 9 does not replicate, and § 7 does not limit its admonition to habitat modification that "actually kills or injures wildlife." Conversely, § 7 contains limitations that § 9 does not, applying only to actions "likely to jeopardize the continued existence of any endangered species or threatened species," 16 U. S. C. § 1536(a)(2), and to modifications of habitat that has been designated "critical" pursuant to § 4, 16 U. S. C. § 1533(b)(2).^[17] Any overlap that § 5 or § 7 may have with § 9 in particular cases is unexceptional, see, e. g., Russello v. United States, 464 U. S. 16, 24, and n. 2 (1983), and simply reflects the broad purpose of the Act set out in § 2 and acknowledged in TVA v. Hill.

We need not decide whether the statutory definition of "take" compels the Secretary's interpretation of "harm," because our conclusions that Congress did not unambiguously manifest its intent to adopt respondents' view and that the Secretary's interpretation is reasonable suffice to decide this case. See generally Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837 (1984). The latitude the ESA gives the Secretary in enforcing the statute, together with the degree of regulatory expertise necessary to its enforcement, establishes that we owe some degree of deference to the Secretary's reasonable interpretation. See *704 Breyer, Judicial Review of Questions of Law and Policy, 38 Admin. L. Rev. 363, 373 (1986).^[18]

III

Our conclusion that the Secretary's definition of "harm" rests on a permissible construction of the ESA gains further support from the legislative history of the statute. The Committee Reports accompanying the bills that became the ESA do not specifically discuss the meaning of "harm," but they make clear that Congress intended "take" to apply broadly to cover indirect as well as purposeful actions. The Senate Report stressed that "`[t]ake' is defined . . . in the broadest possible manner to include every conceivable way in which a person can `take' or attempt to `take' any fish or wildlife." S. Rep. No. 93-307, p. 7 (1973). The House Report stated that "the broadest possible terms" were used to define restrictions on takings. H. R. Rep. No. 93-412, p. 15 (1973). The House Report underscored the breadth of the *705 "take" definition by noting that it included "harassment, whether intentional or not. " Id., at 11 (emphasis added). The Report explained that the definition "would allow, for example, the Secretary to regulate or prohibit the activities of birdwatchers where the effect of those activities might disturb the birds and make it difficult for them to hatch or raise their young." Ibid. These comments, ignored in the dissent's welcome but selective foray into legislative history, see post, at 726-729, support the Secretary's interpretation that the term "take" in § 9 reached far more than the deliberate actions of hunters and trappers.

Two endangered species bills, S. 1592 and S. 1983, were introduced in the Senate and referred to the Commerce Committee. Neither bill included the word "harm" in its definition of "take," although the definitions otherwise closely resembled the one that appeared in the bill as ultimately enacted. See Hearings on S. 1592 and S. 1983 before the Subcommittee on Environment of the Senate Committee on Commerce, 93d Cong., 1st Sess., pp. 7, 27 (1973) (hereinafter Hearings). Senator Tunney, the floor manager of the bill in the Senate, subsequently introduced a floor amendment that added "harm" to the definition, noting that this and accompanying amendments would "help to achieve the purposes of the bill." 119 Cong. Rec. 25683 (1973). Respondents argue that the lack of debate about the amendment that added "harm" counsels in favor of a narrow interpretation. We disagree. An obviously broad word that the Senate went out of its way to add to an important statutory definition is precisely the sort of provision that deserves a respectful reading.

The definition of "take" that originally appeared in S. 1983 differed from the definition as ultimately enacted in one other significant respect: It included "the destruction, modification, or curtailment of [the] habitat or range" of fish and wildlife. Hearings, at 27. Respondents make much of the fact that the Commerce Committee removed this phrase *706 from the "take" definition before S. 1983 went to the floor. See 119 Cong. Rec. 25663 (1973). We do not find that fact especially significant. The legislative materials contain no indication why the habitat protection provision was deleted. That provision differed greatly from the regulation at issue today. Most notably, the habitat protection provision in S. 1983 would have applied far more broadly than the regulation does because it made adverse habitat modification a categorical violation of the "take" prohibition, unbounded by the regulation's limitation to habitat modifications that actually kill or injure wildlife. The S. 1983 language also failed to qualify "modification" with the regulation's limiting adjective "significant." We do not believe the Senate's unelaborated disavowal of the provision in S. 1983 undermines the reasonableness of the more moderate habitat protection in the Secretary's "harm" regulation.^[19]

*707 The history of the 1982 amendment that gave the Secretary authority to grant permits for "incidental" takings provides further support for his reading of the Act. The House Report expressly states that "[b]y use of the word `incidental' the Committee intends to cover situations in which it is known that a taking will occur if the other activity is engaged in but such taking is incidental to, and not the purpose of, the activity." H. R. Rep. No. 97-567, p. 31 (1982). This reference to the foreseeability of incidental takings undermines respondents' argument that the 1982 amendment covered only accidental killings of endangered and threatened animals that might occur in the course of hunting or trapping other animals. Indeed, Congress had habitat modification directly in mind: Both the Senate Report and the House Conference Report identified as the model for the permit process a cooperative state-federal response to a case in California where a development project threatened incidental harm to a species of endangered butterfly by modification of its habitat. See S. Rep. No. 97-418, p. 10 (1982); H. R. Conf. Rep. No. 97-835, pp. 30-32 (1982). Thus, Congress in 1982 focused squarely on the aspect of the "harm" regulation at issue in this litigation. Congress' implementation of a permit program *708 is consistent with the Secretary's interpretation of the term "harm."

IV

When it enacted the ESA, Congress delegated broad administrative and interpretive power to the Secretary. See 16 U. S. C. §§ 1533, 1540(f). The task of defining and listing endangered and threatened species requires an expertise and attention to detail that exceeds the normal province of Congress. Fashioning appropriate standards for issuing permits under § 10 for takings that would otherwise violate § 9 necessarily requires the exercise of broad discretion. The proper interpretation of a term such as "harm" involves a complex policy choice. When Congress has entrusted the Secretary with broad discretion, we are especially reluctant to substitute our views of wise policy for his. See Chevron, 467 U. S., at 865-866. In this case, that reluctance accords with our conclusion, based on the text, structure, and legislative history of the ESA, that the Secretary reasonably construed the intent of Congress when he defined "harm" to include "significant habitat modification or degradation that actually kills or injures wildlife."

In the elaboration and enforcement of the ESA, the Secretary and all persons who must comply with the law will confront difficult questions of proximity and degree; for, as all recognize, the Act encompasses a vast range of economic and social enterprises and endeavors. These questions must be addressed in the usual course of the law, through case-bycase resolution and adjudication.

The judgment of the Court of Appeals is reversed.

It is so ordered.

Justice O'Connor, concurring.

My agreement with the Court is founded on two understandings. First, the challenged regulation is limited to significant habitat modification that causes actual, as opposed *709 to hypothetical or speculative, death or injury to identifiable protected animals. Second, even setting aside difficult questions of scienter, the regulation's application is limited by ordinary principles of proximate causation, which introduce notions of foreseeability. These limitations, in my view, call into question Palila v. Hawaii Dept. of Land and Natural Resources, 852 F. 2d 1106 (CA9 1988) (Palila II), and with it, many of the applications derided by the dissent. Because there is no need to strike a regulation on a facial challenge out of concern that it is susceptible of erroneous application, however, and because there are many habitat-related circumstances in which the regulation might validly apply, I join the opinion of the Court.

In my view, the regulation is limited by its terms to actions that actually kill or injure individual animals. Justice Scalia disagrees, arguing that the harm regulation "encompasses injury inflicted, not only upon individual animals, but upon populations of the protected species." Post, at 716. At one level, I could not reasonably quarrel with this observation; death to an individual animal always reduces the size of the population in which it lives, and in that sense, "injures" that population. But by its insight, the dissent means something else. Building upon the regulation's use of the word "breeding," Justice Scalia suggests that the regulation facially bars significant habitat modification that actually kills or injures hypothetical animals (or, perhaps more aptly, causes potential additions to the population not to come into being). Because "[i]mpairment of breeding does not `injure' living creatures," Justice Scalia reasons, the regulation must contemplate application to "a population of animals which would otherwise have maintained or increased its numbers." Post, at 716, 734.

I disagree. As an initial matter, I do not find it as easy as Justice Scalia does to dismiss the notion that significant impairment of breeding injures living creatures. To raze the last remaining ground on which the piping plover currently *710 breeds, thereby making it impossible for any piping plovers to reproduce, would obviously injure the population (causing the species' extinction in a generation). But by completely preventing breeding, it would also injure the individual living bird, in the same way that sterilizing the creature injures the individual living bird. To "injure" is, among other things, "to impair." Webster's Ninth New Collegiate Dictionary 623 (1983). One need not subscribe to theories of "psychic harm," cf. post, at 734-735, n. 5, to recognize that to make it impossible for an animal to reproduce is to impair its most essential physical functions and to render that animal, and its genetic material, biologically obsolete. This, in my view, is actual injury.

In any event, even if impairing an animal's ability to breed were not, in and of itself, an injury to that animal, interference with breeding can cause an animal to suffer other, perhaps more obvious, kinds of injury. The regulation has clear application, for example, to significant habitat modification that kills or physically injures animals which, because they are in a vulnerable breeding state, do not or cannot flee or defend themselves, or to environmental pollutants that cause an animal to suffer physical complications during gestation. Breeding, feeding, and sheltering are what animals do. If significant habitat modification, by interfering with these essential behaviors, actually kills or injures an animal protected by the Act, it causes "harm" within the meaning of the regulation. In contrast to Justice Scalia, I do not read the regulation's "breeding" reference to vitiate or somehow to qualify the clear actual death or injury requirement, or to suggest that the regulation contemplates extension to nonexistent animals.

There is no inconsistency, I should add, between this interpretation and the commentary that accompanied the amendment of the regulation to include the actual death or injury requirement. See 46 Fed. Reg. 54748 (1981). Quite the contrary. It is true, as Justice Scalia observes, post, at 716, *711 that the Fish and Wildlife Service states at one point that "harm" is not limited to "direct physical injury to an individual member of the wildlife species," see 46 Fed. Reg. 54748 (1981). But one could just as easily emphasize the word "direct" in this sentence as the word "individual."^[*] Elsewhere in the commentary, the Service makes clear that "section 9's threshold does focus on individual members of a protected species." Id., at 54749. Moreover, the Service says that the regulation has no application to speculative harm, explaining that its insertion of the word "actually" was intended "to bulwark the need for proven injury to a species due to a party's actions." Ibid.; see also ibid. (approving language that "[h]arm covers actions . . . which actually (as opposed to potentially), cause injury"). That a protected animal could have eaten the leaves of a fallen tree or could, perhaps, have fruitfully multiplied in its branches is not sufficient under the regulation. Instead, as the commentary reflects, the regulation requires demonstrable effect (i. e., actual injury or death) on actual, individual members of the protected species.

By the dissent's reckoning, the regulation at issue here, in conjunction with 16 U. S. C. § 1540(a)(1), imposes liability for any habitat-modifying conduct that ultimately results in the death of a protected animal, "regardless of whether that result is intended or even foreseeable, and no matter how long *712 the chain of causality between modification and injury." Post, at 715; see also post, at 719. Even if § 1540(a)(1) does create a strict liability regime (a question we need not decide at this juncture), I see no indication that Congress, in enacting that section, intended to dispense with ordinary principles of proximate causation. Strict liability means liability without regard to fault; it does not normally mean liability for every consequence, however remote, of one's conduct. See generally W. Keeton, D. Dobbs, R. Keeton, & D. Owen, Prosser and Keeton on Law of Torts 559-560 (5th ed. 1984) (describing "practical necessity for the restriction of liability within some reasonable bounds" in the strict liability context). I would not lightly assume that Congress, in enacting a strict liability statute that is silent on the causation question, has dispensed with this well-entrenched principle. In the absence of congressional abrogation of traditional principles of causation, then, private parties should be held liable under § 1540(a)(1) only if their habitat-modifying actions proximately cause death or injury to protected animals. Cf. Benefiel v. Exxon Corp., 959 F. 2d 805, 807-808 (CA9 1992) (in enacting the Trans-Alaska Pipeline Authorization Act, which provides for strict liability for damages that are the result of discharges, Congress did not intend to abrogate common-law principles of proximate cause to reach "remote and derivative" consequences); New York v. Shore Realty Corp., 759 F. 2d 1032, 1044, and n. 17 (CA2 1985) (noting that "[t]raditional tort law has often imposed strict liability while recognizing a causation defense," but that, in enacting the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, Congress "specifically rejected including a causation requirement"). The regulation, of course, does not contradict the presumption or notion that ordinary principles of causation apply here. Indeed, by use of the word "actually," the regulation clearly rejects speculative or conjectural effects, and thus itself invokes principles of proximate causation.

*713 Proximate causation is not a concept susceptible of precise definition. See Keeton, supra, at 280-281. It is easy enough, of course, to identify the extremes. The farmer whose fertilizer is lifted by a tornado from tilled fields and deposited miles away in a wildlife refuge cannot, by any stretch of the term, be considered the proximate cause of death or injury to protected species occasioned thereby. At the same time, the landowner who drains a pond on his property, killing endangered fish in the process, would likely satisfy any formulation of the principle. We have recently said that proximate causation "normally eliminates the bizarre," Jerome B. Grubart, Inc. v. Great Lakes Dredge & Dock Co., 513 U. S. 527, 536 (1995), and have noted its "functionally equivalent" alternative characterizations in terms of foreseeability, see Milwaukee & St. Paul R. Co. v. Kellogg, 94 U. S. 469, 475 (1877) ("natural and probable consequence"), and duty, see Palsgraf v. Long Island R. Co., 248 N. Y. 339, 162 N. E. 99 (1928). Consolidated Rail Corporation v. Gott- shall, 512 U. S. 532, 546 (1994). Proximate causation depends to a great extent on considerations of the fairness of imposing liability for remote consequences. The task of determining whether proximate causation exists in the limitless fact patterns sure to arise is best left to lower courts. But I note, at the least, that proximate cause principles inject a foreseeability element into the statute, and hence, the regulation, that would appear to alleviate some of the problems noted by the dissent. See, e. g., post, at 719 (describing "a farmer who tills his field and causes erosion that makes silt run into a nearby river which depletes oxygen and thereby [injures] protected fish").

In my view, then, the "harm" regulation applies where significant habitat modification, by impairing essential behaviors, proximately (foreseeably) causes actual death or injury to identifiable animals that are protected under the Endangered Species Act. Pursuant to my interpretation, Palila II —-under which the Court of Appeals held that a state *714 agency committed a "taking" by permitting mouflon sheep to eat mamane-naio seedlings that, wh