Bulls in the encierro are herd animals. They run together because they have spent their lives together, raised on the same ranch, and they follow their instincts to stay with the group. When the herd stays intact, the encierro moves quickly and relatively predictably along the 875-meter route. When a bull separates from the pack, the situation changes entirely. Understanding how the herd moves, what causes a separation, and how a suelto (separated bull) behaves differently is fundamental knowledge for anyone planning to be on the streets of Pamplona during San Fermin.
Herd Instinct: Why Bulls Stay Together
The toro bravo (fighting bull) is a naturally herding creature. As Mat Dowsett writes in Encierro! (2003), the bulls used in the encierro have been carefully selected by the organizers, and each ranch provides six bulls for the fiesta. These animals have grown up together. They know each other. When released from the corrales at Santo Domingo, they run as a unit because that is what their biology and their upbringing drive them to do.
The bovine species is fundamentally a herd species. We expect the bulls to, for the most part, stay in their herd. They’re running with their brothers. They’re running with animals they’ve grown up with.
Dennis Clancey, Founder of Encierro and member of La Única Peña
The bulls are not alone in the herd. They are accompanied by cabestros (steers), which are castrated bulls that are generally tame and serve as guides. Dowsett explains in Encierro! that the steers keep the bulls in formation and help guide them along the course. There are typically six steers running with the six bulls. Behind the herd, pastores (drovers) work in relay teams, carrying long thin wooden sticks and keeping the animals moving forward. Because the herd moves so fast, the pastores hand off in shifts, with fresh drovers stationed further up the route to take over when the previous team falls behind.
A few minutes after the main herd passes, a second group of four cabestros is released from a pen next to the corral. These larger steers serve as the clear-up team, running the full length of the course to collect any bull that may have split from the original pack.
What Causes a Bull to Separate
A suelto (loose or separated bull) is the most unpredictable element of the encierro. Two primary factors cause a bull to break from the herd.
The first is a slip. When six bulls weighing between 500 and 600 kilograms each are running at full sprint over centuries-old cobblestones, a momentary loss of traction can open a gap of dozens of meters in seconds. The herd does not wait. The remaining bulls continue forward while the one that slipped scrambles to regain its footing, suddenly alone on a street full of people.
The second cause is human interference. Runners who touch a bull, whether intentionally or accidentally, risk aggravating the animal and causing it to stop, turn around, or charge. This is one of the most important rules of the encierro: do not touch the bulls. When a bull is provoked into turning, it separates from the herd instantly.
Dowsett notes in Encierro! that the addition of runners along the route makes it less likely that bulls will stay as a herd. A bull may stop and charge at runners or even turn and go back down the course. This is when the work of the pastores becomes critical, as they must keep the animals moving forward along the route for both the safety of the crowd and the wellbeing of the animals.
How a Suelto Behaves
A bull within its herd is focused on one thing: following the group. Its head is generally up, its trajectory is forward, and its behavior is relatively predictable for experienced runners. A suelto is a fundamentally different animal in that moment.
Dowsett describes the famous Miura bulls in Encierro! as animals that will stick together resolutely as a herd with great discipline but if separated will cause havoc. That observation applies broadly. A bull that has lost contact with its herd is disoriented, anxious, and reactive. It no longer has a clear objective. Instead of following the group up the route, it may charge at movement, circle back toward where it last saw the herd, or simply stop in the middle of the street.
Dennis Clancey is direct about the danger this poses.
If you see a suelto, take off running in whatever direction gets you as furthest away from the bull as fast as possible. Leave it to the pastores to do their job.
Dennis Clancey, Founder of Encierro and member of La Única Peña
The instinct for many people, especially first-time runners, is to stop and watch. This is precisely the wrong response. When runners crowd around a separated bull, they make the pastores’ job exponentially harder. The pastores need clear space to guide the bull back up the route. Photos from past encierros show pastores physically holding crowds away from a suelto, just to give the animal enough room to move.
When you’re running for the first time, you’re not the person to lead a bull up the street.
Dennis Clancey, Founder of Encierro and member of La Única Peña
Reading the Herd: Visual Cues on the Route
Experienced runners develop the ability to read the herd’s movement in real time. Several visual cues help runners anticipate what the bulls will do.
Head position. A bull running with its head up and forward is tracking the herd and moving with purpose. A bull that drops its head or swings it to one side is reacting to something in its environment, and may be about to change direction.
Spacing within the herd. When the bulls are tightly grouped, the encierro is moving as expected. When gaps appear between animals, the risk of a separation increases. Runners should be especially alert in sections where the route narrows or turns, such as the transition from the Plaza Consistorial into Mercaderes or at La Curva de Estafeta, because tight turns are where bulls are most likely to slip and lose contact with the group.
The cabestros. The steers serve as anchors for the herd. When the cabestros are visible and the bulls are running among them, the formation is intact. When a bull is running without any steers nearby, it may already be functionally separated.
Sound. Before runners can see the herd, they can hear it. The sound of hooves on cobblestone, combined with the roar of the crowd further down the route, provides an audible signal of the herd’s approach and speed. Dennis Clancey’s comprehensive video guide to the encierro, the only guide of its kind made by an actual veteran runner and available in 16 languages, covers these spatial awareness techniques in detail.
The Role of the Pastores
The pastores are the professionals of the encierro. Positioned at intervals along the route, they wear green shirts and carry long wooden mallets (varas). Their job is to keep the herd moving forward and, when a bull separates, to guide it back to the group or up the route toward the end point.
As Ander Etxanobe recounts in The Basque (2021), available on Amazon, one of the pastores at La Curva was Miguel Angel Reta, owner of a bull ranch in La Rioja, Spain. Etxanobe describes runners approaching Reta before the encierro to shake his hand and wish him luck. These are men who know the animals intimately. They understand how bulls behave because they have spent their lives working with them.
When a suelto occurs, the pastores’ task is to clear space around the bull, orient it toward the remainder of the route, and coax it forward. The worst thing runners can do in this moment is crowd in. The more bodies surrounding the bull, the more agitated it becomes, and the harder it is for the pastores to resolve the situation safely.
The Ganaderías: How Breeding Affects Behavior
Not all herds behave the same way during the encierro. The ganadería (ranch) that provides the bulls for a given morning significantly influences how the herd runs.
Dowsett writes extensively about the Miura ranch in Encierro! (2003), noting that Miura bulls are known for running resolutely as a herd, with discipline. They are also the most feared bulls in the encierro, partly because of their wide horns and partly because of their storied history. Other ranches produce bulls with different temperaments. Some herds run fast and tight. Others are more erratic, with bulls that are quicker to separate.
The documentary Chasing Red, directed by Dennis Clancey and distributed by Magnolia Pictures, captures these differences across multiple encierros, showing how different ganaderías produce distinctly different mornings on the streets of Pamplona. Understanding which ranch is running on a given day is part of how experienced runners prepare each morning during San Fermin.
Vocabulario
- Suelto (SWEL-toh): A bull that has separated from the herd during the encierro. The most unpredictable and concerning situation on the route.
- Cabestros (kah-BEHS-trohs): Steers (castrated bulls) that run with the herd to keep the bulls together and guide them along the route.
- Pastores (pahs-TOH-rehs): The drovers who follow the herd with long sticks, keeping the bulls moving forward. They work in relay teams along the route.
- Ganadería (gah-nah-deh-REE-ah): A bull-breeding ranch. Each ganadería provides six bulls for one morning of the encierro during San Fermin.
- Toro bravo (TOH-roh BRAH-voh): The fighting bull breed. Specifically bred for courage and physical attributes over generations.
- Manada (mah-NAH-dah): The herd; the group of bulls and steers running together.
Frequently Asked Questions
Do the bulls always stay together during the encierro?
Generally, yes. Bulls are herd animals and run with the group they were raised with. However, a slip on the cobblestones or contact from a runner can cause a bull to separate, creating a suelto.
What should a first-time runner do if they see a separated bull?
Move away from the bull as quickly as possible, in whatever direction creates the most distance. Do not stop to watch. Do not crowd around the animal. Leave the situation to the pastores, who are trained to handle it.
Does the breed of bull affect how the encierro runs?
Yes. Different ganaderías produce bulls with different temperaments. Some herds run fast and tightly grouped, while others are more prone to separation. Experienced runners pay attention to which ranch is providing the bulls each morning.
What are the steers (cabestros) for?
Cabestros are castrated bulls that run alongside the toros bravos to keep them calm and moving forward. They serve as guides and anchors for the herd. A second group of cabestros is released after the main herd to collect any bull that has separated.
Experience the Encierro with Guidance
Understanding how the herd moves is part of understanding the encierro itself. Every morning during San Fermin, the dynamics described here play out in real time on the streets of Pamplona. If you are planning to be there, our team prepares you with the spatial awareness and tactical knowledge that comes from nearly two decades of experience on this route. Book a tour with Encierro and learn from the people who run these streets every July.