But now, a mysterious trend is baffling the zoo's fans and critics, reports CBS News Sharyl Attkisson. A tragic rash of animal deaths in recent months, including a bobcat, tree 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 perfectly 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," says National zoo director Lucy Spelman.
The red pandas were poisoned when caretakers made the mistake of putting toxic pellets in their pen to kill rats. Two top zoo officials were forced out of their position because of the incident and plans are underway to hire a General Curator.
"The actions that I've taken are specific to the red pandas incident," says Spelman. "My feeling is we need a position of a general curator."
Spelman says there are no other deaths due to human error besides the deaths of the red pandas. But it was revealed that, last summer, rampant rats killed at least six prairie dogs — half the exhibit.
Also, Spelman was the head vet when two zebras starved to death three years ago. She had mistakenly ordered a sharp cutback in their food when they were actually undernourished. She was promoted to zoo director months later.
"Somebody needs to look at the whole system from top to bottom," says Human Society spokesman Richard Farinato. "I don't think that in-house is a sufficient look."
Unlike municipal zoos, which are regulated by cities, there's little oversight of the National Zoo (part of the Smithsonian Institution). But Spelman may be fielding questions about the animal deaths in her appearance before Congress.