DULUTH — The Lake Superior Zoo's one-year-old red panda, Pip, was found dead in her den last week, the zoo announced Monday.

The female panda was the zoo's second, having joined Zoozee in April.

The cause of death is unknown, a social media post said.

"Each and every staff member at the zoo is devastated by the loss of Pip," said Haley Hedstrom, the zoo's chief executive officer. "Though she was with us for only a short time, we all quickly fell in love with her charismatic personality."

Pip came from the Buttonwood Park Zoo in Massachusetts where she was born in a litter of two. Her small size at birth led to her name, Pipsqueak.

Security camera footage shows that Pip went into her den box at about 10 p.m. Aug. 1 and did not come out again. Prior to that, no unusual behavior or interference from animals or people had been observed, the zoo said.

Pip has been taken to the University of Minnesota for pathology work. The zoo will share findings from the examinations within the next few weeks.

Animal care staff are monitoring Zoozee, who is in good health.

"Our team is confident that this was an individualized incident," the post said.

Pip was chosen for the zoo by the Species Survival Plan that monitors red pandas within Association of Zoos and Aquariums facilities. Red pandas are native to the eastern Himalayas and southwestern China. The animal is considered critically endangered.

The red panda program at the zoo has become one of its most popular additions, with Zoozee joining last year.