I. The Statutory Framework

The Endangered Species Act of 1973, signed into law by President Nixon on December 28 of that year, is the most comprehensive wildlife protection statute in the world. Its stated purpose, codified at 16 U.S.C. § 1531(b), is “to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved.”¹

Section 9 of the Act, at 16 U.S.C. § 1538(a)(1)(B), provides the operative prohibition. It makes it unlawful for any person subject to the jurisdiction of the United States to “take any such species within the United States or the territorial sea of the United States.” The term “take” is defined at 16 U.S.C. § 1532(19) to mean “to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct.”²

The statute does not define “harass.” The statute does not define “harm.” The U.S. Fish and Wildlife Service, exercising the rulemaking authority delegated to it under Section 4 of the Act, has defined both. At 50 CFR § 17.3, the Service defines “harm” as “an act which actually kills or injures wildlife. Such an 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.”³

The same regulation defines “harass” as “an intentional or negligent act or omission which creates the likelihood of injury to wildlife by annoying it to such an extent as to significantly disrupt normal behavioral patterns which include, but are not limited to, breeding, feeding, or sheltering.”⁴

We draw the reader’s attention to several features of these definitions. “Harm” requires an act that actually kills or injures. “Harass” requires only the likelihood of injury. “Harm” includes habitat modification. “Harass” includes annoying an animal to the point of behavioral disruption. Neither definition requires that the person intend to affect wildlife. Both encompass negligent acts. Both encompass omissions. The definitions do not require that the person know the species is listed. They do not require that the person know the species exists. They require only that the act or omission creates effects on wildlife that satisfy the regulatory criteria.

A porch light is an act. Leaving it on is, alternatively, an omission to turn it off. Either way, the regulatory framework has accounted for it.

II. The Supreme Court’s Confirmation

In Babbitt v. Sweet Home Chapter of Communities for a Great Oregon, 515 U.S. 687 (1995), the United States Supreme Court addressed whether the Secretary of the Interior’s regulatory definition of “harm”—which includes significant habitat modification—exceeded the scope of the statutory term “take.”⁵

The Court held, in a 6–3 decision delivered by Justice Stevens, that it did not. The majority reasoned that the broad statutory definition of “take” was intended to be comprehensive, that Congress used the word “harm” in addition to more specific terms like “hunt” and “trap” precisely because it meant something broader than direct physical capture, and that the inclusion of habitat modification within “harm” was a reasonable interpretation given the ESA’s overarching purpose of protecting ecosystems.

Justice Stevens wrote: “The dictionary definition of the verb form of ‘harm’ is ‘to cause hurt or damage to; injure.’ 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.”⁶

The practical consequence of Sweet Home is that the Section 9 prohibition on “take” extends beyond the hunter with a rifle and the trapper with a snare. It reaches any person whose actions modify the environment in ways that kill, injure, or harass listed species. The Court did not limit this principle to logging, mining, or real estate development. It established that the ESA’s protections apply wherever human activity degrades habitat to the detriment of listed wildlife.

The Court did not address porch lights. But it did not need to. The principle it announced operates without regard to the source of the habitat modification, the intention behind it, or the size of the device causing it.

III. The Body Count

Loss, Will, and Marra, publishing in The Condor: Ornithological Applications in 2014, produced the most comprehensive estimate of avian mortality from building collisions in the United States. Their study, which synthesized data from 23 prior studies, estimated that between 365 million and 988 million birds are killed annually by collisions with buildings.⁷ The authors identified artificial light at night as a significant contributing factor, noting that nocturnal migrants are attracted to illuminated structures, where they become disoriented and collide with glass and other surfaces.

The Cornell Lab of Ornithology, in a 2019 study published in Frontiers in Ecology and the Environment, combined more than two decades of satellite data on light pollution with weather radar measurements of bird migration density across 143 stations. The researchers estimated that approximately 600 million birds die from building collisions every year in the United States and ranked metropolitan areas by the danger they pose to migrants based on the intersection of light pollution levels and migration corridors.⁸

A 2024 study by the American Bird Conservancy, incorporating data on delayed mortality from birds that initially survive collisions but die within days from internal injuries, pushed the estimated annual death toll well beyond one billion.⁹

Of the more than one thousand bird species protected under the Migratory Bird Treaty Act, 92 are listed as endangered or threatened under the ESA. These species migrate at night. They navigate by the stars. When they encounter artificial light, they are drawn to it, circle in confusion, collide with illuminated surfaces, and die. This is not speculation. It is the basis of a peer-reviewed literature spanning four decades, a national Lights Out program operating in more than 50 cities, and a gubernatorial proclamation from the State of Minnesota.¹⁰

Every one of those deaths constitutes an act that actually kills wildlife. Every illuminated building that attracts a listed species into a fatal collision is engaging in significant habitat modification that kills wildlife by impairing essential behavioral patterns, including migration, which the regulations classify as a subset of “sheltering” and “feeding.” The regulatory definition of “harm” does not require that the building owner intended the bird to die. It does not require that the building owner knew the bird existed. It requires only that the act actually killed wildlife. The bird is dead. The act occurred. The definition is satisfied.

IV. The Hatchlings

The most compelling evidence that artificial light constitutes a “take” under the ESA is that the federal government has already concluded it does.

Five of the world’s seven sea turtle species nest on beaches in the United States. All five are listed under the ESA as either endangered or threatened: the green sea turtle (Chelonia mydas), the loggerhead (Caretta caretta), the leatherback (Dermochelys coriacea), the hawksbill (Eretmochelys imbricata), and the Kemp’s ridley (Lepidochelys kempii).¹¹

Sea turtle hatchlings emerge from their nests at night and orient toward the brightest horizon, which on a natural beach is the open ocean reflecting moonlight and starlight. When artificial lights are visible from the nesting beach, hatchlings orient toward the light source instead of the sea. They wander inland, onto roads and into parking lots, where they die of dehydration, predation, or vehicular strike. The Florida Fish and Wildlife Conservation Commission reports that disorientation from artificial lighting causes thousands of hatchling deaths each year in Florida alone.¹²

Florida’s response to this problem has not been to suggest that artificial light does not constitute a take. Florida’s response has been to regulate the lighting. Lee County, Brevard County, Broward County, and dozens of other coastal jurisdictions have adopted Sea Turtle Conservation Codes that require all exterior lighting visible from nesting beaches to be shielded, redirected, or extinguished during nesting season, which runs from May 1 through October 31.¹³ Violations of these ordinances are enforceable under both state law and the federal ESA. The penalties include fines of up to $50,000 per violation and imprisonment of up to one year under civil provisions, or up to $250,000 and five years under criminal provisions.¹⁴

The legal theory under which Florida enforces these ordinances is not novel. It is not creative. It is the straightforward application of the ESA’s take prohibition to a source of artificial light that kills listed species. The hatchling dies because the light was on. The light was on because the homeowner turned it on, or because the homeowner failed to turn it off. The act or omission created the likelihood of injury to wildlife by disrupting its normal behavioral patterns. This is a take under 50 CFR § 17.3. The FWS agrees. Florida agrees. The sea turtles, being dead, have no position.

What Florida has not done is explain why this analysis applies to a beachfront condominium in Brevard County but not to a porch light in Omaha. The loggerhead sea turtle nests on the Florida coast. The Indiana bat (Myotis sodalis), listed as endangered since 1967, forages in the darkness of the Midwest. Artificial light fragments its habitat, reduces its insect prey base, and disrupts its roosting patterns. The regulatory definition of “harass” does not contain a geographic limitation. The statute does not distinguish between coastal and continental photon emissions.

V. The Insects

The ecological pathway from porch light to federal wildlife crime does not require that the listed species itself be drawn to the light. It requires only that the light disrupts the food web on which the listed species depends.

Artificial light at night has been identified in peer-reviewed literature as a significant and underappreciated driver of global insect decline. Owens et al. (2020), writing in Biological Conservation, conducted a comprehensive review of the effects of artificial light on insects across all life stages and identified mechanisms including disruption of movement patterns, alteration of foraging behavior, interference with reproductive signaling, and direct mortality from attraction to light sources.¹⁵

The direct mortality figures are staggering. Eisenbeis (2006) documented that approximately one-third of insects drawn to streetlights suffer direct mortality from exhaustion, heat exposure, or predation at the light source.¹⁶ A single streetlight can kill more than 150 insects per night. The United States has approximately 26 million streetlights. It has considerably more porch lights.

The relevance to the ESA is this: insects are the primary food source for the majority of ESA-listed bird, bat, and amphibian species. When a porch light kills insects that would otherwise be consumed by a listed species, it degrades the habitat of that species by reducing its food supply. When the reduction in food supply impairs the species’ ability to breed, feed, or shelter, the porch light has caused “harm” within the meaning of 50 CFR § 17.3.

The pathway is not hypothetical. Lewis et al. (2020), publishing in BioScience, identified artificial light at night as one of the primary threats to global firefly populations.¹⁷ Fireflies use bioluminescent signals for mate attraction. Artificial light drowns out these signals, silencing mating displays and reducing reproductive success. Owens et al. demonstrated that female fireflies exposed to amber-wavelength artificial light “go almost completely dark,” rendering them invisible to searching males.¹⁸ Several firefly species are under review for ESA listing. The Bethany Beach firefly (Photuris bethaniensis) was listed as endangered in 2022.

The porch light does not need to land on an endangered species to constitute a take. It needs only to degrade the ecosystem on which an endangered species depends. This is precisely the theory the Supreme Court endorsed in Sweet Home. Habitat modification that impairs essential behavioral patterns is harm. Harm is take. Take is a violation of Section 9. The porch light is on.

VI. The Regulatory Double Standard

The federal government does not lack precedent for regulating artificial light to protect wildlife. It has simply chosen to regulate some sources and ignore others.

In 2013, the Federal Communications Commission adopted new rules requiring communication tower operators to replace steady-burning red lights with flashing lights on towers between 350 and 500 feet, based on research demonstrating that steady lights attract and disorient nocturnal migratory birds. The FCC acted on the recommendation of the U.S. Fish and Wildlife Service, which had concluded that steady-burning lights on communication towers constituted a significant source of avian mortality.¹⁹

The legal foundation for the FCC’s action was the Migratory Bird Treaty Act, but the reasoning applies with equal force under the ESA. A steady light on a 400-foot tower kills birds. A steady light on a 10-foot porch does the same thing at shorter range. The physics of phototaxis does not vary with the height of the light source. The bird does not distinguish between a tower beacon and a lantern-style fixture from Home Depot.

The Audubon Society operates Lights Out programs in more than 50 American cities, in which building owners voluntarily turn off non-essential lighting during spring and fall migration seasons.²⁰ A study published in the Proceedings of the National Academy of Sciences, based on more than 40 years of collision monitoring data from Chicago’s Field Museum, found that when half the windows in a building were darkened, bird collisions decreased by a factor of 11 during spring migration and a factor of 6 during fall migration.²¹

The darkened building killed fewer birds. The lit building killed more. The variable was the light. The agency that regulates the take of listed species has not regulated the variable. It has regulated communication towers. It has regulated beachfront condominiums. It has not regulated the light on the front of your house, which operates every night of the year, in every state in the country, within the range of ESA-listed species that are documented to be killed, injured, or harassed by it.

VII. The Incidental Take Permit

Section 10(a)(1)(B) of the ESA, codified at 16 U.S.C. § 1539(a)(1)(B), provides a mechanism by which persons who will incidentally take listed species in the course of otherwise lawful activity may obtain an “incidental take permit” from the Fish and Wildlife Service.²² The applicant must submit a Habitat Conservation Plan specifying the anticipated impact, the steps to minimize and mitigate the impact, and the funding available to implement the plan.

Incidental take permits are routinely issued for land development projects, timber harvesting operations, wind energy facilities, and agricultural practices. The FWS has issued them for activities ranging from highway construction in the habitat of the Delhi Sands flower-loving fly to residential development in the range of the California gnatcatcher. The issuance of an incidental take permit is an acknowledgment by the federal government that the permitted activity constitutes a take, and that but for the permit, the activity would violate Section 9.

No incidental take permit has ever been issued for a porch light. No incidental take permit has ever been issued for a landscape fixture, a security floodlight, a decorative string of lights, a motion-activated spotlight, or a bug zapper. The FWS has not issued zero permits because these devices do not take listed species. The peer-reviewed literature confirms they do. The FWS has issued zero permits because no one has applied for one. No one has applied for one because the FWS has not required anyone to apply. The FWS has not required anyone to apply because it has declined to enforce the statute against residential lighting.

The statute does not contain a residential exemption. The regulations do not contain a residential exemption. The Supreme Court in Sweet Home did not articulate a residential exemption. The exemption does not exist in law. It exists in practice. It exists because the alternative—requiring 130 million households to apply for incidental take permits for their exterior lighting—would require the Fish and Wildlife Service to process more permit applications than it has processed in the entire 53-year history of the Endangered Species Act.

VIII. The Mathematics of Non-Enforcement

The U.S. Census Bureau’s American Community Survey reports approximately 130 million occupied housing units in the United States.²³ The Energy Information Administration’s Residential Energy Consumption Survey reports that more than 90 percent of American homes use exterior lighting.²⁴ Conservatively, 115 million homes operate at least one exterior light on any given night.

The Fish and Wildlife Service lists approximately 1,680 species as endangered or threatened in the United States.²⁵ These species occupy habitat in every state. They include nocturnal species, crepuscular species, and migratory species that fly at night. There is no county in the contiguous United States that does not contain the range of at least one ESA-listed species whose documented behavioral patterns are disrupted by artificial light.

The civil penalty for a knowing take of an endangered species under 16 U.S.C. § 1540(a)(1) is up to $25,000 per violation. If we assume, conservatively, that each illuminated home takes one listed animal per year—a fraction of the documented per-structure mortality rate for migratory birds alone—the aggregate annual penalty exposure across 115 million homes would be approximately $2.875 trillion. This exceeds the combined revenue of the federal government’s five largest agencies.

The criminal penalty under 16 U.S.C. § 1540(b)(1) is a fine of up to $50,000 and imprisonment of up to one year for a knowing violation. We do not suggest that 115 million homeowners should be imprisoned. We observe that the statute permits it.

IX. The Light in the Window

We anticipate the objection that a single porch light cannot meaningfully affect an endangered species. The objection misunderstands the legal standard. The regulatory definition of “harass” does not require that the act produce population-level effects. It requires that the act create “the likelihood of injury to wildlife” by disrupting normal behavioral patterns. A single porch light that attracts a single moth away from its mating flight has disrupted a normal behavioral pattern. If that moth is a member of a species that pollinates a plant on which a listed species depends, the disruption cascades through the food web. If the moth is itself a listed species—and moths are among the least-studied and most frequently petitioned candidates for ESA listing—the disruption is direct.

The objection also misunderstands the problem of cumulative impact. One hundred and fifteen million porch lights are not 115 million independent events. They are a single, continuous, nationwide modification of the nocturnal environment. The nighttime sky of the contiguous United States, as documented by the satellite-derived World Atlas of Artificial Night Sky Brightness, is illuminated above natural levels across more than 80 percent of its area.²⁶ This is habitat modification at continental scale. The Supreme Court in Sweet Home held that habitat modification causing actual injury to listed species is “harm.” The peer-reviewed literature documents actual injury. The satellite data documents the modification. The legal standard is met.

The National Park Service, which manages some of the last remaining dark-sky habitats in the country, acknowledges on its own website that artificial light at night “can cause birds to collide with windows or walls, causing injury, exhaustion, confusion, or death,” that it “interferes with amphibians, who detect light levels 100 times dimmer than humans,” and that it disrupts the vertical migration of zooplankton, “which affects animals up the food chain.”²⁷ The federal government’s own land management agency has published, on its own website, a description of exactly the kind of wildlife injury and behavioral disruption that satisfies its own regulatory definition of “take.”

X. Conclusion

The evidence does not require creative interpretation. The Endangered Species Act prohibits the take of listed species. Take includes harass and harm. Harass includes any negligent act that creates the likelihood of injury by disrupting normal behavioral patterns. Harm includes habitat modification that actually kills or injures wildlife. Artificial light at night does both. The peer-reviewed literature documents avian mortality in the hundreds of millions, hatchling disorientation by the thousands, insect mortality at continental scale, and behavioral disruption across taxa from bats to fireflies to zooplankton.

The Fish and Wildlife Service knows this. It recommended that the FCC regulate tower lighting to protect birds. It cooperated with Florida to enforce coastal lighting restrictions to protect sea turtles. It administers an incidental take permit program that has processed applications for highway overpasses and Christmas tree farms. It has not processed a single application for a porch light.

Approximately 115 million American homes operate exterior lighting every night, across the range of 1,680 listed species, producing documented mortality and behavioral disruption that satisfies every element of the regulatory definitions of “harm” and “harass.” The annual take is not in the hundreds. It is not in the thousands. Measured in insects alone, it may approach the trillions. Each individual take is a violation of 16 U.S.C. § 1538(a)(1)(B). Each violation carries a civil penalty of up to $25,000. The aggregate annual exposure is a number with thirteen digits.

The Fish and Wildlife Service employs approximately 8,000 people. It would need to hire considerably more. Or it would need to do what it has done for the past 53 years, which is to pretend that the largest source of light-induced wildlife mortality in the Western Hemisphere is not subject to the most comprehensive wildlife protection statute in American law.

The light is on. The statute is on the books. The species are on the list. The deaths are in the literature.

Ergo.