So when she was diagnosed with cancer — which is unusual for penguins in captivity — the zoo decided to get her the best treatment possible.
You can see clips of Tess's treatment at Colorado State University in the video above. Her tumor (a pinto bean-sized mass on the side of her face) was shot with a 29-minute, 59-second dose of radiation focused into a tiny, precise beam. The treatment was so noninvasive that Tess went back to the zoo that very evening.
Two weeks later, she was reunited with the other penguins. She and her 33-year-old mate, Mongo, settled back into their nest.
"If you didn't know her, you would never guess she's as old as she is," Kathy Wolyn, a Pueblo Zoo veterinarian, said in a statement. "That's why we wanted to pursue further treatment for her tumor."
Tess's keepers see her as a beacon of hope for her dwindling species. In the wild, most of her kind don't live past 20. And as commercial fishing makes competition for food in the penguins' native habitat of South Africa more dire, populations continue to dwindle. According to the Pueblo Zoo, their captive population has enough genetic diversity to sustain breeding for at least 100 years.