To mitigate bird collisions, enforce the Migratory Bird Treaty Act

Billions of birds embark on long-distance migrations between breeding and nonbreeding areas each spring and fall worldwide (e.g., ref. 1). Birds, which mainly migrate at night, often do not survive this most treacherous period of their lives. Adverse weather and climate are their biggest natural challenges, but a large and growing number are killed in collisions with reflective and transparent glass in buildings.

Birds, such as the Dickcissel (Spiza americana) pictured here, are increasingly threatened by light pollution, hard-to-detect glass structures, and other parts of the built environment. There are ways to help. Image credit: Ryan Sanderson (photographer; eBird S89077010).

How many? Estimates suggest some 388–965 million birds die annually in the United States in building collisions—a staggering 30 deaths per second (2). This decade-old number is almost certainly an underestimate, given the thousands of buildings with such glass that have since been constructed (3), which include single-story residential homes, buildings four stories tall or lower, and prominently illuminated urban skyscrapers.

Light attracts and disorients birds, drawing them to areas full of collision hazards (4, 5). Birds do not perceive glass and other reflective and transparent materials as solid, and flying at full speed into these materials almost certainly kills or severely injures them (6). Collisions with buildings, in conjunction with predation by cats, loss and conversion of habitat, pollution, and other factors, have together caused the loss of nearly a third of North American breeding birds in the past half-century (7).

What can be done? Bird-safe glass and building designs exist, as well as methods to eliminate unnecessary light pollution. Techniques like these would mitigate the risk to birds from existing and new construction. And legislation has been proposed to force developers to adopt them. Introduced last year, the Federal Bird Safe Buildings Act (8) would require any federal building constructed, acquired, or significantly altered to incorporate bird-safe building materials and design features. But this bill has yet to pass, and voluntary adoption of its innovations has been slow. Further, the proposed act covers only future construction or alteration of federal buildings, with existing structures unaffected.

Needless Death

We recently witnessed a grim demonstration of why that bill, and more effort, are needed. The McCormick Place Lakeside Center in Chicago saw a spectacularly large collision event on the early morning of October 5, 2023, the result of high-intensity migration, poor visibility, and severe thunderstorms, as well as an urban environment with plentiful light and reflective and transparent glass. Nearly 1,000 birds were killed, including more than 30 different species, such as palm (Setophaga palmarum), yellow-rumped (Setophaga coronata), and Tennessee (Leiothlypis peregrina) warblers and swamp (Melospiza georgiana) and white-throated (Zonotrichia albicollis) sparrows (Fig. 1).

Fig. 1.

A major bird collision event occurred in Chicago on the night of October 4–5, 2023, with 954 birds killed at McCormick Place Convention Center. (Left) Specimens assembled in the Field Museum of Chicago. (Right) Identities and numbers of these individuals in the Field Museum collection. Warbler illustrations, from top to bottom: Tennessee (L. peregrina), magnolia (Setophaga magnolia), palm (S. palmarum), and yellow-rumped (S. coronata). Image credit: Photos by Daryl Coldren (The Field Museum, Chicago, IL); illustrations by David Quinn (artist, © Lynx Edicions and Cornell Lab of Ornithology).

The largest convention center in North America, this enormous structure on the shore of Lake Michigan has killed thousands of migratory birds since its construction (e.g., ref. 9). Collision mortality has been recognized as a major issue in Chicago for many years, and local volunteers do all they can to study and to prevent such deaths. But the city remains the worst in the United States for exposing migratory birds to light pollution (10).

The October event was sadly predictable. A publicly available forecasting system has been in place since 2018 to accurately predict nightly passage of migrating birds across the contiguous United States, providing 72 hours’ notice of bird movements (11). And, based on 20 years of collision data at this Chicago building, researchers have demonstrated that decreasing lighted window area there could reduce bird mortality by 60% (12).

The convention center does participate in the Lights Out Chicago program (13), an initiative started in 2000 by the Chicago Audubon Society in cooperation with the Mayor’s Nature and Wildlife Committee and the Building Owners and Managers Association of Chicago, that asks buildings to turn off or dim lights after 11 PM. However, before this collision event, lights were out only when the building was not in use; illumination during convention center events shone brightly through unshaded and untreated windows. It’s been a problem for many mortality events at the site over the last 40 years.

The Chicago incident was a clear demonstration of what’s at stake. After many previous requests from the local birding, academic, and conservation communities, this building appears to be responding to significant public pressure (e.g., a large petition, editorials) with efforts seeking to address long-standing issues of the lack of shaded and treated windows. But bird collisions are not a one-building problem—e.g. more than 1,500 birds were killed among an array of other buildings in Chicago in the early morning hours of 5 October—or a single-city problem. Indeed, residential homes kill approximately the same number of birds annually as do urban buildings. Copious peer-reviewed literature documents the impacts of reflective and transparent building materials and the attractive and disorienting effects of artificial light on almost every continent. Numerous solutions have been suggested, including recommendations for materials, designs, and operations, spanning planning; preconstruction and postconstruction; and commercial, residential, public, and private spaces.

A Search for Solutions

Inexpensive and increasingly less expensive and available bird-safe solutions for residential homes include treated glass; stickers and designs in appropriate patterns (e.g., refs. 14–16) to make glass visible; reducing nonessential lighting; redirecting exterior and interior lighting; and installing window shades indoors and/or screens outdoors. These can reduce bird mortality. Yet, while there have been great strides in increasing awareness of these solutions, their adoption is not universal—far from it, given the continued death toll beneath windows. Slow uptake is likely multifaceted, a combination of apathy, limited promotion, and lack of knowledge.

We argue that, across residential and urban landscapes, communities need laws and enforcement to reinforce educational efforts and voluntary compliance. This will protect birds and reduce building strikes. Such strong action should have public support in the United States, where 96 million people identify as birdwatchers (17). And there is already active legislation on the US books that could be used: the Migratory Bird Treaty Act of 1918 (MBTA) (18).

We argue that, across residential and urban landscapes, communities need laws and enforcement to reinforce educational efforts and voluntary compliance. This will protect birds and reduce building strikes.

The MBTA was enacted to ensure the protection of all migratory bird species. Technically, the Act made it a crime to pursue, hunt, take, capture, kill, or sell migratory birds or their parts, including nests, eggs, and feathers. In an era of rampant avian destruction, when punt guns cut through flocks of birds and market hunters decimated populations, the Migratory Bird Treaty Act of 1918 was a monumental legislative achievement, especially for protection of commercially traded species like herons and egrets. Now, we need to adapt this far-reaching law as a primary, top-down enforcement tool—to protect birds from modern threats posed by light and glass, much the same as the original legislation and Congressional activities that outlawed the use of punt guns.

Using the MBTA to prevent bird–building collisions depends on legal interpretation of whether the Act prohibits the so-called “incidental take” of migratory birds, which means deaths that result from, but are not the purpose of, an activity. The US government has indicated that it does and that strikes with glass buildings do count as incidental take. But circuit courts have disagreed.

The US Fish and Wildlife Service (USFWS) should clarify the position. It can do so by finalizing and publishing its “Advance Notice of Proposed Rulemaking” from October 2021 (19) that says incidental take is prohibited under the MBTA—and so action can be taken to drastically reduce, or even prevent, many collisions.

Under current interpretation and USFWS policy, bird deaths from building collisions appear to meet the conditions for priority enforcement of the MBTA. The USFWS (20) says it will prioritize enforcement where incidental deaths are the result of “activities by a public- or private-sector entity that are otherwise legal; are foreseeable; and occur where known general or activity-specific beneficial practices were not implemented.” Mass bird deaths from building collisions—those that number in the hundreds or thousands of birds nightly or annually—are the result of an entirely foreseeable failure to implement “known beneficial practices.”

Policy Prescription

The massive mortality at Chicago’s McCormick Place seems an ideal test case for USFWS enforcement and an opportunity to use the incidental take interpretation. The magnitude of the deaths, the known history of bird deaths from this building, mortality predicted by models, and the failure to take known steps to shade and to treat windows that could have avoided the deaths all fit well within USFWS enforcement priorities. Such enforcement would send the message to large building operators in major avian flyways around the country that failure to take reasonable precautions could result in MBTA enforcement and a serious fine. In this case, reasonable precautions not taken would have been to employ window shades to control illumination and treat windows to make them visible to birds.

Stricter enforcement of the MBTA is not a panacea, but it could incentivize more widespread implementation of bird-friendly designs and operations, rather than rely on the court of public opinion to effect such changes, as appears to be the case with McCormick Place presently.

Along with better enforcement, USFWS could increase awareness by working collectively with partners—whether other federal agencies, conservation nonprofits, or scientific institutions—to develop public service announcements and other informative messaging, as the agency has already done for communication towers and power lines.

While we wait for federal action, some US cities are making much-needed changes. Several have passed or are working on mandatory bird-safe building standards, including Washington, DC; San Francisco; New York; and Chicago. These laudable and important efforts still do not go far enough in protecting birds. For example, in Chicago, Ordinance 02020-136 prioritizes deterrence strategies to reduce bird collision, though, unfortunately, many building projects are not covered by this ordinance; the enforcement is challenging because of shortages in Department of Public Development staffing.

Birds are the proverbial canary in the coal mine, serving as proxies for ecosystem connectivity and the presence of pollutants. They actually help indicate a nation’s environmental health. Although we have many tools for protecting them, we can do a much better job. This starts with the MBTA.