More fallout after our Contact 13 hidden camera investigation on conditions at the Las Vegas Zoo. Las Vegas Mayor Oscar Goodman has received a letter from a national organization in Washington, DC saying it's finally time for the city to step-in and do something for the animals.

The letter from the Humane Society of the United States tells Mayor Goodman that the Las Vegas Zoo fails to live up to the positive image he's creating for Las Vegas. They cite animals alone, in extreme heat, not protected and in small barren cages with no meaningful stimulation.

At the zoo Monday, there were more pigeons than patrons, a health hazard the zoo's been written up for, and one of many highlighted in our recent undercover investigation.

"I think we have to look at the quality of lives of these animals," said Linda Faso, a local animal activist.

That's exactly what Contact 13 did with a hidden camera and help from the Humane Society of the United States.

"The enclosures are way too small for the species that are in them. The zoo was incredibly hot. It has a lack of shade in almost every enclosure. The social needs of most of the animals are not being met," said Jane Garrison.

Our investigation got the mayor's attention.

"We are on top of it. The city is going to send some folks out there and if there is a problem, we will rectify it," said Mayor Goodman at his weekly press conference.

The HSUS wants to hold him to that. The President of the nation's largest animal protection organization sent a letter Monday from Washington, DC.

In the letter to the mayor, the National Humane Society asks the city to do three things: require the improvements necessary to bring this zoo up to the standards of an accredited facility; in the time it takes to do that, reduce the number of animals here by sending those on loan back to the San Diego zoo; and help the zoo with immediate changes to cover their enclosures so the animals are no longer vulnerable.

"I think they've had an awful lot of problems. I think for years pat has tried to get the city behind him to help financially, to give him a boost of any kind," said Linda Faso. 

The city did. Once, giving him a hefty loan that he later defaulted on, landing the zoo in a lawsuit. We went back again Monday to try to talk to zoo director Pat Dingle, the man who's been ducking us for weeks.

They invite us in, only to find out dingle is gone for the day.