Mammoth, Wyo. — Actor Pierce Brosnan, who pleaded guilty Thursday to stepping off a trail in a thermal area during a November visit to Yellowstone National Park, was caught after posting pictures online, court records said.

Brosnan, who called into the court hearing in Mammoth, Wyoming, was fined $500 and ordered to make a $1,000 donation by April 1 to Yellowstone Forever, a nonprofit organization that supports the park, court records said. Prosecutors had recommended a $5,000 fine and a two-year probationary sentence.

A second petty offense, for violating closures and use limits, was dismissed by U.S. Magistrate Judge Stephanie Hambrick.

The actor issued an apology on his Instagram account Thursday, saying he "made an impulsive mistake" and calling himself an environmentalist with "the utmost respect for and love of our natural world."

"I deeply regret my transgression and offer my heartfelt apologies to all for trespassing in this sensitive area. Yellowstone and all our National Parks are to be cared for and preserved for all to enjoy," Brosnan wrote.

He didn't see a "no trespassing" sign when entering the thermal area to take a photo and didn't hike in the immediate area, he wrote.

Brosnan ended the message with "#StayOnThePath."

Brosnan, 70, walked in an off-limits area at Mammoth Terraces, in the northern part of Yellowstone near the Wyoming-Montana line, on Nov. 1, according to citations issued by the park. He was in the park on a personal visit and not for film work, the U.S. Attorney's Office for Wyoming has said.

However, he uploaded images of himself standing in the snow on the thermal feature to his Instagram page, court records said.

Mammoth Terraces is a scenic spot of mineral-encrusted hot springs bubbling from a hillside. They are just some of the park's hundreds of thermal features, which range from spouting geysers to gurgling mud pots, with water at or near the boiling point.

Going out-of-bounds in such areas can be dangerous: Some of the millions of people who visit Yellowstone each year get badly burned by ignoring signs warning them not to stray off the trail.

Getting caught can bring legal peril, too, with jail time, hefty fines and bans from the park handed down to trespassers regularly.

Brosnan appeared in four James Bond films, starred in the 1980s TV series "Remington Steele" and is known for starring roles in the films "Mrs. Doubtfire" and "The Thomas Crown Affair."

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• Pierce Brosnan
• Yellowstone National Park