PHOTO – A waterfall cascades over a cliff and flows into a stream down a rocky creek.
NPS / Addy Falgoust

JACKSON (WNE) — A grizzly bear mother with cubs was likely responsible for an attack that left two hikers in Yellowstone National Park seriously injured on Monday, the park said in a Friday update.

Evidence from the attack suggests that the female grizzly involved likely had two or three cubs born over the winter. The park’s investigation is ongoing.

The park also released the ages of the hikers, who were brothers, on Friday. One is 15 years old and the other is 28. Emergency responders transported them to Eastern Idaho Regional Medical Center by helicopter following the incident.

The attack occurred on the Mystic Falls Trail near Old Faithful.

RELATED: Yellowstone bear attack site was closed to spring hiking until 2024 to reduce human-grizzly conflicts – 

As of Tuesday, one brother was in serious condition and the other was in critical condition. A spokesperson from the hospital did not respond to a request for a Friday status update by press time.

The conflict came “a little early” for the park, Tim Reid, Yellowstone’s chief ranger, said at a Wednesday meeting of Greater Yellowstone Ecosystem grizzly managers.

“This whole winter has set the stage for everything being early,” Reid said. “The area this incident occurred in is outside of Old Faithful where normally you’re postholing in snow. Visitors have taken advantage of good hiking conditions.”