“Shooting wild pigeons in Iowa” from Frank Leslie’s Illustrated News, 1867, depicting hunters and dogs shooting at a flock of passenger pigeons. These once-common birds went extinct in 1914, largely due to overharvesting. Image via Wikimedia Commons.

Is killing birds a necessary evil if it benefits a special interest?

By Dr. Stanley Temple, Wisconsin’s Green Fire Ambassador

In the late 19^th and early 20^th centuries there was a large-scale industry based on killing birds for profit and personal gain. The unregulated business of market hunting is estimated to have killed hundreds of millions of birds annually during that time. The fledgling bird conservation movement made their case by appealing to American’s hearts and minds. Put briefly the case was: even though killing birds was economically profitable, it was wrong.

The resulting Migratory Bird Treaty Act of 1918 (the MBTA) was the nation’s first major victory for bird conservation. It empowered the federal government to prohibit the killing of most migratory birds and to regulate the killing of other species, such as migratory game birds. With the MBTA’s passage, migratory birds were finally recognized as part of the public trust. The federal government formally accepted responsibility to manage and protect migratory birds for the greater benefit of society.

A central purpose of the MBTA is now under assault. The federal government is abdicating much of its responsibility for protecting migratory birds. This new contrived reinterpretation of the MBTA would allow special interests to kill birds without consequences if it is not done deliberately and, by the way, just happens to also reduce their costs of doing business. Given this threat to the MBTA and our birds, let’s revisit the early conservation success story of the MBTA and its implications today.

An evolving ethic of responsibility

So, how did the MBTA come to be and why has it endured for over a century as one of the foundations of our nation’s commitment to conservation? The MBTA was initially somewhat controversial and was the culmination of years of strategizing and lobbying that finally succeeded in overcoming several obstacles. The biggest hurdles were overcoming states’ rights issues and lobbying by the market hunting industry.

Through tireless efforts of early conservationists and conservation organizations, public opinion shifted in favor of protecting birds from unregulated slaughter. George Grinnell and the Audubon Society which he founded in 1901 played central roles. Obvious declines of many of the birds being killed for personal gain and the extinction of the Passenger Pigeon in the wild in 1902 eventually turned the tide against the market hunting industry and other types of unregulated killing of birds. An ethic of responsibility evolved that required those who killed birds for personal gain to be held accountable by society for the negative consequences of their actions.

The cause inspired a generation of conservationists, including a teenage Aldo Leopold who wrote to his parents in 1905 upon learning that waterfowl were being killed by market hunters:

“I am very sorry that the ducks are being slaughtered, but of course could expect nothing else. When my turn comes to have something to say and do against it and other related matters, I am sure that nothing in my power will be lacking to the good cause.”

Historic photograph from “Conservation of fish, birds and game,” 1916, Canada Commission of Conservation. Image via Wikimedia Commons.

Shifting from state to federal authority

At the time, the federal government had never been involved explicitly in bird conservation. Authority for protecting birds lay with the states. As such, the federal government’s first attempt to protect migratory birds was controversial, and the Weeks-McLean Act of 1913 was promptly deemed unconstitutional as an infringement on state’s rights. To overcome that obstacle, a different strategy evolved: have the Executive Branch enter the US into an international treaty. Then lobby Congress to ratify the treaty and codify the obligations of the treaty into the law of the land.

The Migratory Bird Treaty between the United States and Canada was signed in 1916. Each country pledged to protect the migratory birds they shared across their borders, providing a uniform policy across the continent rather than an unworkable patchwork of state and provincial policies. Congress did its part and passed the MBTA in 1918. The supremacy of federal obligations under an international treaty allowed the Act to prevail over the constitutional challenges that had doomed the earlier Weeks-McLean Act.

Acceptance of the MBTA leads to species recoveries

The MBTA made it “unlawful at any time, by any means or in any manner,” to pursue, hunt, take, capture, kill, possess, sell, purchase, barter, import, export, or transport any migratory bird or their parts, nests or eggs, unless authorized by the Secretary of the Interior. “Take” has been clarified in enabling regulations to mean “pursue, hunt, shoot, wound, kill, capture, or collect.” Since 1918, the protection of migratory birds has become an accepted part of American culture. Harming migratory birds has increasingly become regarded as immoral as well as illegal.

The Migratory Bird Treaty was subsequently updated to allow certain uses by Native Americans (1962) and to include Mexico (1936), Japan (1972), and Russia (1976).

The Migratory Bird Treaty Reform Act of 2004 clarified exactly which bird species were covered. Currently over 1,100 species are protected. Because the MBTA has been so successful, many bird species that were threatened by unregulated killing a century ago have recovered.

Duck banding at Minnesota Valley National Wildlife Refuge. Ducks are inspected to determine sex and age. Data is recorded along with the band number. Duck in foreground is a male wood duck in eclipse plumage. Photo by Tina Shaw/USFWS via Flickr. Wood ducks are protected under the MBTA.

Billions of birds still killed through human actions

Despite the MBTA’s success, the 2025 “State of the Birds Report” concluded that a third of American bird species have declined by 50% or more since 1970. Long-term monitoring of bird populations has shown that some three billion birds have vanished since 1970. The causes of those declines are complex, and some major threats, such as habitat loss and climate change, are not covered under the MBTA.

But human actions still result in killing birds, even if some of the ways we kill birds are not as deliberate as they were in 1918. These deaths are from “incidental take,” which means the killing resulted somewhat unintentionally during otherwise lawful activities. A 2017 meta-analysis   estimated the average number of birds killed annually in the United States by “incidental take” as follows:

• Collisions with building glass, 599,000,000
• Collisions with communication towers, 6,600,000
• Collisions with vehicles, 214,500,000
• Collisions with wind turbines, 234,012
• Electrocutions on transmission and distribution lines, 5,600,000
• Poisoning, 72,000,000
• Landing in open oil pits, 750,000
• Predation by free-ranging house cats, 2,400,000,000

Of the alarming losses, and excluding vehicles and cats, over 700 million annual deaths were due to incidental take by industries, organizations, government agencies, and individuals while engaged in “business as usual.”

Brown et al., 2020: Figure 3: Ten Cedar Waxwings dead from collisions on two adjacent buildings.
Photo credit: Bill Hanewinkel. (https://peerj.com/articles/9401/)

Legal consequences for “incidental take” of migratory birds

Although the MBTA has long held violators accountable for their incidental taking, the issue currently at hand is whether incidental take of migratory birds should be prohibited at all by the MBTA. Until recently, penalties were imposed for killing of large numbers of birds in a single event. For example, the 2010 Deepwater Horizon explosion and oil spill resulted in catastrophic deaths of over a million birds in the Gulf of Mexico. The MBTA forced BP to pay $100 million in fines.

Legal action was also pursued if an offending party ignored repeated warnings of their chronic incidental take and failed to make reasonable efforts to reduce bird deaths. In most cases of chronic incidental take, authorities worked with offenders to find compromises that reduced bird deaths and avoided penalties. For example, a major bird collision mitigation project at Chicago’s McCormick Place happened after negative publicity over the recurring annual deaths of many hundreds of migrating birds when they collided with the convention center’s expansive glass façade. There was also potential liability under the MBTA if the problem wasn’t addressed. As a result of glass modifications, during the 2024 fall migration season, bird fatalities dropped by over 95% compared to 2023.

In a few high-profile cases, repeat offenders were prosecuted after they refused to compromise and mitigate their incidental take. In 2002, federal courts ruled that the U.S. Navy repeatedly violated the MBTA by bombing a seabird nesting colony during training exercises. Congress quickly reacted by exempting the incidental take of birds during “military readiness activities.” In 2012, federal courts dismissed charges against oil and gas companies for the recurring deaths of thousands of migratory birds killed in their open oil pits, despite repeated warnings to correct the chronic problem. These decisions were significant setbacks because they did not result in penalties for what appeared to be clear cases of incidental killing of migratory birds.

Heavily oiled Brown Pelicans captured at Grand Isle, Louisiana on Thursday, June 3, 2010 waiting to be cleaned of Gulf spill crude oil at The Fort Jackson Wildlife Care Center in Buras, LA. Photo Credit: IBRRC

Back and forth interpretations of the MBTA

An all-out assault on the MBTA had been unleashed. The Act has become a political football, part of larger debates over government regulations. Special interests that were inconvenienced by complying with the MBTA lobbied that they should not be liable for incidental taking while engaged in otherwise legal activities, even if large numbers of birds were killed by their actions. In 2015, Congress tried to include a rider in Department of Justice’s budget appropriations bill that would have prohibited the federal government from prosecuting anyone for any reason for violating the MBTA. That failed, and a follow-on bill also failed to amend the MBTA to exempt from criminal liability any taking, killing, or other harm to a migratory bird that was incidental to an otherwise lawful activity. Migratory birds seemed to be winning in federal courts as well in the court of public opinion where some has indicated that two-thirds of registered voters support the purposes of the MBTA.

Then, in December 2017, just as the conservation community was preparing to celebrate the 100^th anniversary of the MBTA, the Department of the Interior issued a shocking legal opinion reinterpreting the MBTA to exclude incidental take. The reinterpretation meant that incidental killing or harm to migratory birds would no longer be illegal. In 2020, federal courts overturned that reinterpretation, ruling it was inconsistent with the law’s unambiguous prohibition of killing migratory birds. The cynical reinterpretation also ignored the MBTA’s long record of success and decades of enforcement experience and case law. But in January 2021, just before leaving office, the outgoing Trump administration rushed through another attempt to exclude incidental take from prosecution under the MBTA. During its first month in office in February 2021, the incoming Biden administration quickly rescinded that rule.

Most recently, in April 2025, the new Trump administration reinstated its earlier 2017 opinion that incidental take was not covered by the MBTA. Although it will again be challenged in court, that change means that special interests, especially energy industries currently favored by the administration, can kill migratory birds and not be held accountable for incidental take during otherwise legal activities. Furthermore, there would be no incentive to implement measures to avoid foreseeable bird deaths that might be preventable. The ongoing legal struggles over the MBTA will continue and probably end up in the US Supreme Court.

Sandhill Cranes flying at night past the moon. Photo by Robert Rolley, used with permission. Sandhill cranes are protected under the MBTA.

Why has this issue become so controversial?

The controversy boils down to a classic dispute. On one side are the special interests that want to be freed of the regulatory burden of ensuring birds aren’t being killed by their activities (and penalties if they are). They present their case as a strict interpretation of the original motivation for the MBTA, which was enacted in response to deliberate killing of migratory birds. It is, therefore, argued that only deliberate killing of migratory birds is unlawful. Under that view, the incidental take of migratory birds by businesses would essentially be treated as an externality that should not take a toll on their bottom lines, with any negative consequences of killing birds being borne by society.

On the other side is the public interest in protecting America’s birdlife as a valued part of the nation’s public trust. The MBTA has been repeatedly interpreted as prohibiting the killing of birds, regardless of the motive. Just because the threat in 1918 was deliberate killing by market hunters rather than incidental take doesn’t change the fundamental purpose of the law. That purpose has always been to protect migratory birds from being killed by human activities. Even if one sides with special interests, the question of motive alone doesn’t hold up. Once chronic offenders have been notified that they are killing birds and they are offered the opportunity to mitigate the deaths, their choice to ignore the warnings and continue killing birds renders their behavior a deliberate act.

What can we do to protect the Migratory Bird Treaty Act?

As this political tug of war unfolds, the conservation community needs to rally around the MBTA and not take the Act for granted. It is under serious threat and needs to be vigorously defended, as it has been by generations of conservationists. Taking a proactive stance could even include promoting positive changes. A short list of positive changes could include:

• increasing fines to truly deterrent levels;
• explicitly adding poisoning to the list of prohibited acts;
• always holding corporations, organizations, and governments as well as individuals liable for killing birds, regardless of motive;
• clarifying when incidental take will be prosecuted;
• and exempting purely accidental, minor mortality.

The MBTA could be improved to better protect birds and clarify some of its provisions, but it shouldn’t be weakened or ignored just to excuse the killing of migratory birds by politically favored special interests.

Stanley A. Temple

Beers-Bascom Professor Emeritus in Conservation

University of Wisconsin-Madison

and

Senior Fellow

Aldo Leopold Foundation

and

Ambassador

Wisconsin’s Green Fire

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Editor’s note:

Dr. Temple’s essay captures important information about the United States’ conservation legacy in the Migratory Bird Treaty Act (MBTA), providing information about its history and its meaning for today. While our work at WGF usually focuses specifically on Wisconsin, we see how conservation challenges cut across political and geographic boundaries. We encourage you to continue learning more about topics like the MBTA. With this or any conservation issue, you have the power to influence actions in your community and the decisions made by your elected officials. Contact us with your questions or concerns any time.