Grazers Move Mountains
How terracettes are formed by energy-efficient animal movement
HOw are teracettes formed- can a cow make geometry on mountainsides?
In the Swiss countryside, Ben, a QBIOS PhD student in the Bhamla lab, asks himself, “Where did these lines of grass come from along the mountains?” Curious, he consults research papers, and finds that these are called “teracettes”, and the literature attributes these formations to “soil creep”, in which soil slowly slips down a slope and gathers in ridges. Though grazers such as cows and goats are prevalent along the slopes, the literature contends that animals tracking through soil simply cannot affect topology of mountainsides in such a geometric and prominent way.
Curious, the researcher asks himself, “Is that really true?” To answer this, he enlists the help of his lab— the Bhamla Lab.
This source attributes teracette formation to soil creep.
While grazing animals like cattle have long been linked to the formation of terracettes, the mechanism by which their meandering paths could create repeating patterns remains unclear. To explore this, we developed an agent-based model in which simulated grazers interact with a sloped terrain. As each agent moves, it alters the landscape, influencing its own path and that of others. The model shows that large-scale patterns can emerge from the local decisions of uncoordinated grazers as they seek to forage efficiently while minimizing energy costs.
Major questions
1) What factors must be incorporated into an agent-based model determining how the agent walks?
2) In the simulation, how does the agent forage and affect the soil?
3) How can teracette formation be quantified?
4) What trade-offs does the agent weigh when foraging on slopes?
What we’ve discovered
We encode an optimal foraging theory for the agent’s decision-making
When selecting a movement direction, agents attempt to maximize resource intake – to offset maintenance costs and maximize fitness. It also attempts to minimize elevation change – moving uphill is costly, and moving downhill is uncomfortable. These factors influence their random walk dynamics.
Terracette formation is governed by energetic sensitivity and cost of travel
To test the model results, we needed to quantify how “terracette-ed” a hillside really is. Like the ridges on a finger, the distinct ridges along the slope and their straightness can be quantified using fingerprint analysis. Analysis revealed that the agents created deeper and straighter terracettes as the hill slope (and the agents’ sensitivity to it) increased.
Teracette formation reinforces the straight-line path
When locomotion incurs a slope-dependent energetic cost, the model shows that terracette-like bands emerge solely from repeated trampling and reciprocal feedback with the substrate, without explicit communication among agents or auxiliary geomorphic processes. This trade-off between locomotion cost and forage intake echoes field observations: cattle and goats favor cross-slope routes and terracette treads to minimize vertical work, and larger animals – paying higher energetic penalties – follow straighter terraces than smaller ungulates.
Patterns are formed by organisms throughout nature
Our model makes a clear, testable prediction: large-scale terracette geometry emerges from local movement rules that trade energy against forage on sloped terrain. More broadly, it underscores how decentralized agents interacting with a dynamic energy landscape self-organize into persistent, long-range-ordered networks, a motif that recurs in active matter systems, vascular and branching architectures, and the formation of ant and pedestrian trails.
Read the paper
Moving mountains: grazing agents drive terracette formation on steep hillslopes. arXiv (2025).