Yellowstone National Park is warning visitors to take extra caution around bull elk as mating season is approaching.

According to a recent alert from the National Park Servic, park goers should always keep a respectable distance from wildlife, however that’s especially true during the mating season, which typically takes place in September and October. In the summer, there are anywhere from 10,000 to 20,000 elk in the park living in six to seven different herds.

“Bull elk are unpredictable and much more aggressive during this time of year and people have been severely injured,” the NPS wrote in a statement. “Elk run quickly and may change direction without warning. Attacks can be unprovoked and unpredictable.”

During mating season, or the “rut” as it’s commonly called, elk can typically be seen in the northern range, including by Mammoth Hot Springs, as well as by the Madison River, according to the NPS. Calves are then born in May to late June.

The NPS said travelers should always keep at least 75 feet between them and an elk — or the length of two full-sized buses — and to back away immediately if an elk approaches them. Travelers should also look around corners before exiting a building or walking around a blind spot in case there’s an unsuspecting animal there.

If an elk does charge, the NPS said visitors should shelter in their vehicle or run “behind a tall, sturdy barrier as quickly as possible.” And if shelter is not available, they should simply run.

Capturing photos of wildlife is one of the coolest activities in Yellowstone, but visitors should never approach or pursue an animal to take their picture. Instead, the NPS recommends travelers use a lens with a focal length of 300 mm or more. 

Male elk, or bulls, weigh about 700 pounds and stand about 5-feet-high at the shoulder. Female elk, or cows, weigh about 500 pounds and tend to be shorter than their male counterparts. Male elk may also be seen with antlers, which start growing in the spring, but usually drop in March or April of the next year.

They typically eat grass, sedges, other herbs and shrubs, the bark of aspen trees, conifer needles, burned bark, and aquatic plants.