As deforestation and other human-driven land-use changes rapidly fragment natural habitat around the world, it’s no wonder scientists are warning of a sixth mass extinction. Nor is it surprising they are calling increasingly for biological corridors, a conservation strategy recognized for over a half a century but not used anywhere near as widely as experts deem necessary.

Biological corridors connect two or more larger areas of habitat—ideally protected lands—to enable the movement of animals and plants between them, thereby strengthening the genetic diversity of flora and fauna in both locations.

To serve their purpose, the corridors can be “adjoining areas of secondary vegetation or non-intensive production,” says Juan Bezaury-Creel, director and founder of the nonprofit Mexican Biodiversity Foundation (FBD). Non-intensive production, such as agroforestry, can help ensure local livelihoods without disrupting the connectivity of flora and fauna, he notes. Activities such as monocrop agriculture, by contrast, destroy ecological connectivity and balance by creating a genetic barrier.

“The integration of mosaics of varied land use across the landscape allow the flow of species, populations and genes the length of the biological corridors and represents a viable strategy for the conservation of biodiversity and the environmental services nature provides humanity,” says Bezaury-Creel, previously Mexico representative for U.S.-based The Nature Conservancy.

In practice, however, establishing corridors, both terrestrial and aquatic, means humans “must urgently look beyond themselves and understand the impact of their actions,” says Elizabeth Soto, a marine biologist and researcher at Fundación Terram, a Chilean nonprofit. “[W]e must understand the delicate and complex interaction between species and with their habitats, otherwise the intended benefits will remain on paper.”

Experts wish that in the Western Hemisphere, strong biological connectivity could be established from Alaska to Tierra del Fuego, including adjacent ocean waters. Creating a Pan American corridor would require “the use of the wide range of instruments available to plan land and water use, while guaranteeing conservation schemes, restoration, sustainable management of natural resources and the establishment of synergies between the public policy and social action instruments,” Bezaury-Creel says.

Stitching fragmented habitat together would not just facilitate the free movement of species, genes, seeds and pollen, scientists say—it would also help improve stability of the ecosystem. While establishing so-called structural connectivity—creating corridors of conserved forest, for instance—in many ways represents the greatest challenge, it’s not the only one. Another is restoring what scientists refer to as functional connectivity. This means ensuring there are healthy populations of the native species needed to facilitate the movement of organisms and processes.

“Although structural connectivity does not guarantee functional connectivity, it is a very good start,” says Bezaury-Creel, author of a book titled Connectivity for the Conservation of Biodiversity in Mexico. “It takes much longer to restore an entire forest than to promote functional connectivity in an existing habitat by, for example, controlling hunting.”

Umbrella species such as the endangered jaguar (Panthera onca) have informed the design of biological corridors largely on account of the large land area they require to hunt for food and find mates—some 30 to 100 square kilometers (12 to 39 sq. miles), experts say. Land conservation on the scale needed to protect that species by definition improves conditions for other species in the same habitat.

The Gran Calakmul region of Mexico’s Yucatán peninsula is considered to have the largest jaguar population north of Venezuela’s Orinoco Basin—almost 2,000 of the animals, according to Mexico’s National Commission for Natural Protected Areas (Conanp). Gran Calakmul encompasses the national natural protected areas of Calakmul, Balam kin, Balam kú and Bala’an K’aax, which together total a million and a half hectares (3.7 million acres).

In an ongoing collaborative study now in its eighth year, the conservation groups World Wildlife Fund (WWF) and the Wildlife Conservation Society (WCS) have detected 150 jaguars living in the border region of Mexico and Guatemala. Camera-trap images have confirmed that at least three of them roam back and forth between Mexico’s Gran Calakmul and Guatemala’s Reserva de Biosfera Maya, Guatemala’s largest natural protected area spanning 2,090,667 hectares (5,166,150 acres).

“Those jaguars that are crossing national borders are an indicator of how important it is to foster binational cooperation and financing for connectivity,” says Lizardo Cruz, a Mexican biologist who has been working on wildlife conservation since 2005, including 10 years in the Gran Calakmul area.

The Gran Calakmul is deemed to have relatively good connectivity. But the region is not without its challenges due to the encroachment of industrial agriculture and infrastructure such as road and rail construction, says Cruz, now director of projects at Natural Spaces and Sustainable Development (Endesu), a Mexican conservation nonprofit. A prime risk to jaguars and other wildlife is being run over on motorways or rail lines. (See "Controversy over Yucatán train’s impact on animals" —EcoAméricas, January 2025.)

The bio-connectivity challenge can also be heightened by border barriers such as those the United States has erected along its boundary with Mexico. Soto terms such obstructions a “brutal affront on species, resulting in an unacceptable loss of biodiversity.”

While birds can fly over obstructions, the inability of many ground species to do so has in some cases prompted the installation of fauna passageways such as dedicated bridges and tunnels above or below highways. In practice, these are fraught with difficulty, not least ensuring wildlife will learn to use them. Conservationists say that in the case of Mexico’s Tren Maya, fauna passes are insufficient in number or size, in some cases prone to flooding, and in others avoided by animals because humans use them.

Fauna passes are considered a positive and improvable innovation, and green advocates are encouraged they have begun to be addressed in transport and communications planning. But experts note that in Mexico and many other countries in the region, the concept of bio-connectivity is not formally recognized and used in the legal system.

“The greatest impediment to connectivity in Mexico is the absence of public policy with a legal foundation to uphold it, and the corresponding funds to foster connectivity,” says Bezaury-Creel. “It is hard to design policies when the concept does not yet exist. We urgently need connectivity to exist in the legal system so public policies can be created and connectivity can become a reality that is implemented.”

Mexico has 16 biological corridors, according to Conanp, 12 on land and four in its coastal waters. They border 232 Natural Protected Areas (ANPs) that collectively cover 99.2 million hectares (245 million acres), almost 12% of the nation’s land area.

A further 1.2 million hectares (3 million acres) are voluntarily created, privately managed protected lands which increasingly in recent years have been established to serve as corridors. Called Voluntary Conservation Use Areas (ADVCs), they comprise property of various ownership types ranging from private to communal and even in some cases government-held.

The ADVCs are an attractive means of land preservation because they take less time and bureaucracy to establish than the government-created and government-managed Natural Protected Areas.

Their use as conservation corridors has been promoted by Bioconnect, a project funded by the French Development Agency (AFD). Bioconnect has focused in part on providing planning and administrative support for the establishment of ADVCs that create bio-corridors between protected areas.

The first Bioconnect project in Mexico spans 245,000 hectares (605,000 acres) in the Sierra Occidental of Mexico’s Pacific coast state of Jalisco, a region of great cultural and biological diversity. “Jalisco has been a great laboratory for this model because it already had the socio-cultural conditions necessary,” says Karla Barclay, Project Leader for AFD Mexico. Its success has led to Bioconnect being implemented in 12 different parts of Mexico, including Chiapas, Sonora, Guanajuato, Oaxaca, Puebla and Sinaloa states.

Bioconnect Jalisco has fostered corridors in areas where landholders engage in activities including coffee farming, cattle ranching, logging, handicrafts and fruit and jam production in biodiversity-friendly ways. The program encourages participants to adopt sustainable practices and checks up periodically to ensure they are doing so.

“What distinguishes the Jalisco project is its voluntary nature,” says biologist Noé Castellanos, coordinator of the Jalisco project. “People are voluntarily drawn to the model when they see production is sustainable and that they will be able to hand the tradition down to future generations. This drives them to take it on wholeheartedly. For example, regenerative cattle ranching is becoming the norm, yet conservation is not the aim. Rather, it’s integral management of the natural and cultural patrimony. So by default, conservation is achieved.”

The policy challenge of creating corridors is not confined to land. Experts say water bodies, particularly rivers, must be kept healthy and biodiverse so they can help strengthen ties between terrestrial habitats. Too often, the aquatic link is compromised by dams, water pollution and other intrusions, they add.

“Rivers are channels of connectivity par excellence, but legally it has proven very difficult to protect them,” says Javier Warman, natural-resource director for the World Resources Institute in Mexico.

For her part, Soto points seaward and to the need to ratify the “High Seas Treaty.” The binding agreement aims to advance marine biological connectivity by protecting large areas of ocean in international waters, those beyond countries’ 200-nautical-mile territorial limit. (See "Region credited for advancing High Seas Treaty" —EcoAméricas, June 2023.) Over 100 countries signed the U.N. agreement in 2023, but only 17 have ratified it—less than a third of the 60 needed for the treaty to take effect.

Gloria Tavera, conservation director of Mexico’s National Commission for Natural Protected Areas, sees bio-corridors as crucial to multiple aspects of her country’s environmental-policy goals.

“Mexico’s biological corridors provide the environmental services that regulate carbon and water cycles, protect pollinators and seed spreaders and maintain forest cover,” she said. “They are also a fundamental part of the national strategy to confront the effects of climate change.”