But now, reports CBS News Correspondent Sharyl Attkisson, a mysterious trend is baffling zoo fans and critics alike. There's been a rash of animal deaths - a bobcat, kangaroo, seal, lion, tiger, two giraffes, two red pandas, and a hippo.
Amid the deaths, there are now questions about how the animals were cared for. Critics say in some cases the animals died needlessly because of misdiagnosis or mismanagement on the part of zoo officials.
The head of the zoo insists it's a normal life cycle for a zoo with hundreds of mammals.
"All of the animals that have died, with the exception of the red pandas, which shouldn't have happened, died of either old age or disease," said National Zoo Director Lucy Spelman.
"We have some of the best animal caretakers here - veterinarians, curators, keepers - everybody cares for the animals, everybody loves the animals. I mean, it's a very, very caring place. We're sad when animals die. Maybe sometimes people will say, 'Well, what else could we have done,' but I'm very proud of the organization, everybody does an excellent job," she said.
The pandas were poisoned when caretakers put toxic pellets in their pen to kill rats. Because of that, Spelman forced out two top employees and said she'll hire a general curator. But she was evasive on whether other animals also died due to human blunders.
"The actions that I've taken are specific to the red panda incident," she said. My feeling is this organization needs a position of a general curator, and that's someone who's solely focusing on the day-to-day animal care, and someone who reports to me as part of the senior staff. My hope is that change will prevent something like the red panda incident."
Spelman said there were no other deaths besides those CBS News asked about. However, shortly after the interview it was revealed that last summer, rampant rats killed at least six prairie dogs - half the exhibit.
And it turns out Spelman was the zoo's chief vet three years ago when two zebras starved to death; she had mistakenly ordered a sharp cutback in their food when they were actually malnourished.
She was promoted to director months later.
The National Zoo is part of the Smithsonian Institution and has little independent oversight. But Congress has now asked Spelman to appear at routine hearings on the Smithsonian Tuesday. For now, zoo officials are working to put more emphasis on their fantastic births instead of their untimely deaths.