Migratory Bird Treaty Act

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Why it matters

The Migratory Bird Treaty Act (MBTA), 16 U.S.C. § 703-711, makes it unlawful to take (“harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct”) individuals of most bird species found in the United States, unless that taking is authorized by a permit. These protected bird species face many dangers in the form of long-line fishing, oil pits and spills, high-tension power lines, communications towers, and other large infrastructure. Bird deaths attributed to these activities and structures are known as “incidental (or unintentional) takes”. Enforcement of the MBTA has served to limit these incidental takes by incentivizing companies to develop and implement best practices and technologies to safeguard protected birds.

Many more birds are killed by incidental takes than direct takes, and for the past fifty years or so, both have been prohibited under the MBTA. Excluding incidental takes from the MBTA removes the incentive for companies and government agencies to protect birds. According to studies by the Audubon Society, this change could put up to 64 million birds per year at risk. 

Current Status

Incidental takes are no longer illegal under the MBTA. The Trump administration, in Department of the Interior’s Solicitor’s Opinion M- 37050, permanently withdrew the Obama administration’s Solicitor’s Opinion M-37041, which had affirmed that incidental taking of migratory birds was prohibited. 


In 1918, following a treaty between the U.S. and Great Britain to protect migratory birds, Congress passed the Migratory Bird Treaty Act. The MBTA gave authority and responsibility to the U.S. Fish and Wildlife Service to enforce the act and protect birds listed in the MBTA.

Since being delegated authority to enforce the MBTA, the U.S. Fish and Wildlife Service has long recognized incidental takes as part of the prohibition on unauthorized taking of migratory birds.

On January 10, 2017, the Office of the Solicitor for the Department of Interior issued a Solicitor’s Opinion memorandum, M- 37041. Opinion M- 37041 established that “incidental takes were unauthorized taking or killings prohibited under the MBTA.

Trump Era 

On December 22, 2017, the Office of the Solicitor for the Department of Interior issued a Solicitor’s Opinion memorandum, M- 37050, permanently withdrawing Opinion M-37041.

The Trump administration’s interpretation finds that the MBTA’s prohibitions on pursuing, hunting, taking, capturing, killing apply only to affirmative actions that intend to take or kill migratory birds, their nests, or their eggs.

On January 10, 2018, a bi-partisan group of former Department of Interior officials, including  two former Deputy Secretaries of the Interior and five former Directors of the Fish and Wildlife Service, sent a letter to Interior Secretary Ryan Zinke requesting that the Department suspend the new interpretation of the MBTA and convene a bipartisan group of experts to consider the issue.

Thank you to Harvard Law student Leilani Doktor, JD 2019 for her assistance with this rule.

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