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Animals vs. Walls: The Effects of Border Barriers on Animal Populations

Alex MacLennan (J.D. Candidate, Class of 2024) is a contributor. His interests include international and comparative law, US and foreign elections, history, and economic policy. Alex holds a B.S. in Industrial Design from the University of Cincinnati. Before law school, he did product design work for various companies. He speaks enough French and German to be useful in continental European travel.

Construction of a border fence between the United States and Mexico near Yuma, Arizona, in 2020.
Construction of a border fence between the United States and Mexico near Yuma, Arizona, in 2020.

The American ocelot population numbers less than 120 members, making it “one of America’s most endangered cats.” These felines have litters of two or three kittens and a fine fur that makes them targets for hunters. One thing they do not have is a passport.

But why should they need a passport given that immigration laws do not apply to wild animals? Well, even though animals may not be interested in borders, borders are interested in them. A growing number of border walls now restrain the movement of animal populations—the endangered American ocelot included. Typically built to stifle human movement, these walls now threaten animal movement with a particularly detrimental effect on migratory and threatened species. This article looks at the scope of this issue, where it exists, and potential solutions.

The Problem

In general, governments built border walls to keep out people—not animals. The proffered reasons for the walls have included a rise of nationalistic politicians, opposition to refugee movements, and a concern over smuggling. Whether walls work to keep out humans is questionable but there is strong evidence they work to keep out animals. Today, such walls can be found in many parts of the world and animals are paying the price.

Walls in Europe

Europe has seen a return of border walls over the last several years as political leaders react to the refugee crisis. But while humans have found ways around the walls, animals have been less successful.

Unfortunately for European animal populations, these walls can disrupt migration patterns and access to resources. Consider the small band of lynx in the Białowieża Forest traversing the Polish-Belarusian border. These cats have seen their habitat divided since the Polish government built a 115-mile long, 18-foot wall along the border. Cut off from their broader range, the lynx face greater difficulty in finding food and mates threatening individual survival and genetic diversity in the already small population. It is little wonder that a letter signed by over 500 wildlife scientists warned of consequences including “the collapse of the Polish lowland lynx population.”

Nor are the lynx alone. The same letter notes the “pan-European importance” of the forest and how it is the “main dispersal route of large mammals.” Beyond the lynx, the border wall threatens species of bison and brown bears.

Walls in Asia

Asian animals too are threatened by border walls. Fencing along the border between India and Bangladesh has disrupted the movement of Asian elephants in their natural range. Further, walls in Central Asia have blocked camels, bears, snow leopards, and many other animals.

In one example, a wall on the border between Kazakhstan and Uzbekistan blocked the migration of antelope between their seasonal habitats. Without intervention that convinced the Kazakh government to open part of the wall, the antelope faced starvation.

Walls in the United States

The wall on the US-Mexico border has not been particularly effective in restraining human movement but it still manages to threaten animal movement. In addition to the previously mentioned ocelot, the wall also threatens Sonoran pronghorns, Mexican gray wolves, and Peninsular bighorn sheep. As in other border wall cases, the division of these animal populations threatens to reduce already limited genetic diversity and impede their ability to adapt to a changing climate.

The wall even threatens habitats before its completion due to the environmental impact of construction. In an effort to expedite construction, the 2005 Real ID Act gave the Department of Homeland Security the authority to waive laws—including environmental laws—that stood in the way of the wall’s completion. The result has been destruction of the physical landscape and threats to environmentally sensitive areas such as the Tijuana Estuary Reserve. Not surprisingly, many wildlife groups are concerned about the impact of the wall on animal populations including one paper signed by nearly 3,000 scientists.

Potential Solutions

Perhaps the simplest solution would be to just get rid of all the walls, but political reality makes that a tough sell. Furthermore, there are limited situations where walls restricting animal movements may carry benefits, at least to certain groups. Such examples include a fence erected by Botswana that was built to keep out cattle with foot and mouth disease but has the side effect of limiting movements of giraffes, elephants, and zebras.

How to work environmental concerns into political reality is always an ongoing conversation but there are some ideas worth considering.

Wildlife Gates

Creating passageways through the walls is a frequently-proposed solution but has yet to fully realize its promise. On the surface, it seems like the best of both worlds: the wall still serves its intended purpose but allows animals to pass.

But reality is murkier. First is a fundamental engineering and behavioral conundrum. If the wall is to serve its purpose, it must be effective in keeping out people. Smaller gates could allow some animals to pass without letting people through but that would only allow small animals to pass. Certainly any gate large enough for a bear is large enough for a person.

Second, people are smarter than animals. Not only would people be better at finding the openings, but they would likely be able to solve any challenge that an animal could solve.

If the gates were sufficiently guarded, the first two problems may be solvable but that still leaves a third problem: wildlife gates cannot work if they remain closed or unbuilt. In Poland’s case, the government promised 24 wildlife gates that have failed to materialize. Critics call the wildlife gate promise a “soothing agent” and question the idea of animals queuing up for the gate to open.

Thus, while wildlife gates may be part of the solution, there must be the will to implement them in an effective way. For now, this remains challenging given opening gates would either increase security costs, decrease the wall’s effectiveness toward humans, or both.

Convention for the Protection of Migratory Birds

International cooperation can lead to the domestic protection of migratory animals. One of the largest examples of this in the United States is the Convention for the Protection of Migratory Birds signed between the US and Canada. The Convention seeks to preserve migratory birds and save them “from indiscriminate slaughter.”

Both countries passed implementing legislation shortly after signing the Convention. Canada did so with the Migratory Birds Convention Act in 1917 and the US followed with the Migratory Bird Treaty Act of 1918. In Canada, the legislation led to the creation of Federal Migratory Bird Sanctuaries and regulations regarding hunting and commercialization. In the US, the law survived a constitutional challenge and currently protects over 1,000 bird species from activities including hunting and commercialization. As US District Court Judge Valerie Caproni noted in a 2020 case, “[i]t is not only a sin to kill a mockingbird, it is also a crime.”

There are important lessons to learn from this long-standing convention. Primarily, it provides an example of how international cooperation is possible to address threats to animal species. In fact, the US went on to sign similar conventions with Mexico, Japan, and the Soviet Union. It also shows how international agreements can be functional when properly enforced domestically.

But the parallels are not perfect. Migratory birds did not affect the movement of people in and out of the country. Not everyone agreed with the Migratory Bird Treaty Act at the time, but immigration and the border polarize the modern political conversation in a way that migratory birds never did. Overall, the Convention provides a ray of hope through its principles of international cooperation to solve a migratory animal issue but it is not a perfect parallel to today’s situation.

Convention on the Conservation of Migratory Species of Wild Animals

Bilateral treaties such as the Convention for the Protection of Migratory Birds are a good first step, but addressing the issue of animals and walls around the world may require intergovernmental action at the United Nations level. Fortunately, there is already a framework in the Convention on the Conservation of Migratory Species of Wild Animals.

Among the Convention’s fundamental principles is that “[t]he Parties acknowledge the need to take action to avoid any migratory species becoming endangered.” The Convention further acknowledges that the Range States shall endeavor “to prevent, remove, compensate for or minimize, as appropriate, the adverse effects of activities or obstacles that seriously impede or prevent the migration of the species.” Thus, there is a recognition by the 133 Parties to the Convention that there is a need to mitigate obstacles affecting animal species.

But like many international agreements, this Convention is only as powerful as the will to implement and enforce it. Given the previously discussed problems with animals and border walls, it seems that much of the Convention’s goals remain to be realized. Thus, it remains up to activists, experts, and political actors to achieve these goals. They can point to the Convention as a source of authority - even if it is not a panacea for the problem.


Governments may build walls to affect human movement but they have the (usually) unintended effect of restricting animal movement. For species with small populations, these restrictions reduce chances of mating and limit genetic diversity. And for migratory species it can mean being cut off from seasonal habitats. There are solutions that could mitigate the problem—what is needed is the political will.



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