For Migratory Species, Fences Don’t Make Good Neighbors

To survive in the rugged and sprawling grasslands of the Masai Mara ecosystem, herds of white-bearded wildebeest must overcome a gauntlet of dangers: hungry lions, treacherous rivers—and increasingly, fences. 

By disrupting ancient wildebeest migration routes, fences and human-made barriers jeopardize not only wildebeest herds but the health of the entire ecosystem, says Smithsonian ecologist Jared Stabach. Straddling the border between Kenya and Tanzania, the Masai Mara is an ecological stronghold that’s home to approximately 25% of Kenya’s wildlife. 

Since 2010, Stabach has studied and tracked large-scale herd migrations of wildebeest and other animals across the region. Together with partners at the Global Initiative on Ungulate Migration (GIUM), Stabach has published fine-detailed maps and associated tracking data that reveal a troubling trend: fences are dramatically altering seasonal herd movements over time. 

“Over the past ten years, the Mara ecosystem has undergone profound changes and offers a warning to other grassland ecosystems facing similar human pressures,” says Stabach, the terrestrial science lead with the Smithsonian’s Movement of Life Initiative. “As land use shifts in East Africa, there is a tremendous conservation urgency in this region.” 

Across species, migrations are becoming more difficult. For ungulates – hoofed mammals like zebras, antelope or deer – rapid human development in the form of fences and other infrastructure is cutting off migration routes around the world. The rate of landscape change is often occurring faster than conservationists can adequately map and protect the routes the animals move along.  

The GIUM, a project implemented under the auspices of the UN Convention on the Conservation of Migratory Species, is made up of scientists and migration experts from around the world. Based on animal tracking data, GIUM migration maps and associated fact sheets help guide conservation and infrastructure development planning and provide spatial information on where key movement corridors need to remain open for the migrations to persist. The Mara wildebeest migration is the newest map published in the Atlas.

In the past, over 100,000 wildebeest migrated from their wet season range in the western portion of the Greater Mara Ecosystem towards their dry season range on the Loita Plains in the northeast. In the early 1980s, land tenure changed across the region, with land adjacent to the Reserve sold and subdivided for agricultural and private use. The fencing of private land expanded rapidly in the mid-2010s, fragmenting areas across Narok County.  

Fences now block key migratory pathways. Recent movement data collected by Stabach and colleagues indicate that most wildebeest now live a resident lifestyle, with very few animals still migrating to the east to reach their former wet season range on the Loita Plains. Although ungulate migrations are being altered and shortened around the globe, it is rare for researchers to see and document such a dramatic collapse in real time. GIUM analysts estimate that the total area of the migration footprint has been reduced by nearly 90 percent since 2020. 

Migration and population abundance often go hand in hand. No longer able to move long distances to access water, forage and calving grounds at critical points in their life cycle, the Mara wildebeest population has declined precipitously from over 100,000 individuals to less than 25,000, according to estimates provided by the Wildlife Research and Training Institute (WRTI) and the Kenya  Directorate of Resource Surveys and Remote Sensing (DRSRS).  

In a study published in 2022, Stabach and colleagues reported that man-made disturbance is limiting wildebeest movements in other grasslands across East Africa. Climate change-fueled droughts compound this loss of habitat for animals like wildebeest, which move hundreds of miles in massive herds to find food and water.  

Once lost, migration is difficult to restore, as animals often travel on routes that have been learned and refined over generations. However, in other parts of Africa fence removal has led to the recovery of historic ungulate migrations. Conservationists believe that careful, nuanced planning that balances both the needs of people and wildlife in shared landscapes can allow migratory wildebeest and other wildlife to thrive.  

“Maps are a fundamental tool in guiding conservation decision making,” says Dr. Joseph Ogutu, a scientist with the University of Hohenheim in Stuttgart, Germany, who collaborates with Stabach. “Human development and wildlife migration in Kenya don’t have to be exclusive, and maps can pinpoint where animals most need freedom of movement. Yet, ongoing development has driven the collapse of all Kenya-based migrations, shifting the imperative from conservation alone to active habitat restoration. Maps are essential for reopening and reconnecting blocked or lost migration corridors." 

Analyses led by Stabach and published in 2025 pinpoint areas where fences could be removed to facilitate the greatest amount of connectivity for the least amount of cost, highlighting practical recommendations on ways to most effectively reestablish migration across this increasingly threatened ecosystem. Until those changes are made, the research team will continue to study this population’s movements and the impact of fencing on the herd’s survival.