Updated 7:27 p.m., 12/13/2013
Washington (CNN) - A blistering internal report released this week is revealing big problems at the National Zoo and prompting a Congressional review.
On Wednesday, an endangered horse rammed into a fence inside its barn. A gazelle and an antelope-like animal broke their necks the same way. And a hog died from possible malnutrition.
Last month a zebra severely injured an animal keeper. Earlier this year Rusty the red panda got out, and a vulture escaped its enclosure. Both were recaptured.
"You don't hear this happening at zoos across the country. It certainly shouldn't be happening here at our National Zoo," Cathy Liss, president of the Animal Welfare Institute, said.
A safety inspector with the zoo said human error was the cause of the zebra attack, according to CNN affiliate WJLA. Gates were not properly closed between the zebra's stall and the yard where the keeper was working, leading the two to be in the same enclosure. A nearby gazelle was apparently spooked by the attack and ran into a fence, breaking its neck.
An internal investigation of the Cheetah Conservation Station, which houses cheetahs and other African savanna animals, found "animal care and overall organization, accountability, follow-up and communication are severely lacking."
But Pamela Baker-Masson, a spokesperson for the National Zoo, told CNN, "We never compromise safety and well-being of animals."
Officials point out that the zoo was again accredited in September by the Association for Zoos and Aquariums "after an extensive and rigorous review."
As for the deaths or escapes of the animals, officials say they've taken steps to prevent repeat episodes. The budget may also be partly to blame. The zoo does not charge admission, and Congress has cut $2 million over the past few years.
"This is where we look at ourselves very carefully, and we have to review what resources are available," Baker-Masson said.
A spokesperson for Ranking Member of the House Administration Committee Robert Brady said the Congressman has scheduled a briefing with Smithsonian officials to assess the problems.
"[Brady] wants to hear specifically how budget cuts could have led to this situation, and will offer additional comment after those discussions," the spokesperson said.
Some animal welfare advocates point out there've been no problems with the Zoo's star attractions, like the giant pandas.
The panda cubs get naming ceremonies, and the newest tigers receive around-the-clock attention.
"The lesser-known species, the less charismatic species aren't getting the attention that they clearly need," Liss said.
And they're giving the National Zoo attention it clearly doesn't want.
– CNN's Ashley Killough and Mary Grace Lucas contributed to this report.