MINNEAPOLIS (WCCO) – When an 18-month-old dolphin named Taijah died at the Minnesota Zoo Monday night, it was a rough moment for the staff that was there from the time she was born.

“It was a lot of tears upstairs last night,” said Kevin Willis, director of biological services at Minnesota Zoo.

There is something about dolphins — we humanize them, we personify them.

“We anticipate the births, we celebrate successes, certainly the staff and I think the guests mourn the losses,” said Willis.

Since 2006, six dolphins have died at the Minnesota Zoo. Taijah’s cause of death hasn’t been pinpointed, but the early necropsy results show “she had an ulcer between her second and third stomach chambers. looked like a blood clot was blocking food going into her stomach,” Willis explained.

Now, the zoo has just two dolphins: Taijah’s 24-year-old mother Allie and her 48-year-old father, Semo, the oldest male dolphin ever in captivity.

But since 2006, six dolphins have died in the Dolphins’ pod in Apple Valley. Each dolphin death was different: One died during birth, another hit his head on a wall. There was a dolphin with a birth defect, and Taijah. Two others likely died of old age, according to the zoo.

“The median life expectancy of a 1-year-old dolphin in human care is about 25 years, which is about twice what it is for animals in the wild,” said Willis.

Taijah’s death was “unusual, but not unheard of,” Willis said, explaining that just 3 percent of dolphins that make it to 1 years old die before age 2.

“Do animals live longer in a zoo than they would out in the wild?” asked WCCO reporter Jason DeRusha.

“I would say yes, in general,” said Willis. “It makes sense: they’re not worried about food, not worried about predators. But we don’t always know everything animals need for a healthy social life.”

For example: wild tigers live to around 12 years old. In zoos, they live up to age 20.

“The ones that do the best are the ones that have a good domestic analog. The Asian wild horse, we do well with because horse medicine applies pretty directly. A lot of the cats we do well with,” said Willis.

Dolphins generally do well, but “elephants are something we are working on,” he said.

Some studies say wild elephants live as long, or longer, than elephants in zoos.

According to Willis, animals die at a zoo far more than anyone hears about, but the number of deaths isn’t indicative of a good or bad zoo. He said it varies from year to year, based on the age of the animals and the make-up of the zoos collection of species.

By law, zoos report “significant deaths” to the United States Department of Agriculture, and the USDA inspects the Minnesota Zoo twice a year.

“We welcome the scrutiny. If we did something or didn’t do something we want to know,” he said. “We want to learn from this.”