CARING for animals is not just a job … it's a very noble vocation for the dedicated zookeepers at Johannesburg Zoo.

Cherry van der Walt, keeper of large carnivores

 "IT'S just a matter of hours before she gives birth," Dominic Moss says excitedly as he peers at the bontebok's swollen belly. "I can't wait."

Then the Johannesburg zookeeper hops back onto his motorbike and rushes to the polar bear enclosure to check on Wang's condition. This week a wart was removed from its head, but the polar bear - one of only two in Africa - has recovered.

It's all in a day's work for Moss. The 33-year-old curator of the large mammals section at Johannesburg Zoo, nestled in leafy Parktown, spends his days - and sometimes his nights - scouting the expansive zoo on his motorbike.

He checks the condition of the zoo's mammals, conducts research and, of course, talks to the creatures, addressing them by name. After four years at the zoo, many of the animals know his voice and his gentle manner.

"Come piggies," he calls to a family of plump Red River hogs. They dart out of their riverside enclosure to hear Moss give them his friendly morning greeting. Down the road a herd of endangered Bongos, a central African antelope, nuzzle Moss's hands as he feeds them carrots.

Like their guardians, the zoo's 2000 creatures have their "on and off" days. "You have to know when an animal is not in a good mood and respect that…I find that animals are often better to work with than people," jokes Moss.

And animals, too, do not keep office hours. "I can't remember when last I left work at 4pm - animals don't keep time like we do," says Moss. "I'm often here late at night, checking too see if the animals are okay, making sure they are healthy, or chasing those that have escaped."

Escapes do happen, although rarely. Moss recently had to catch and tranquilize a female hippo who had unwittingly escaped from her steely enclosure late one night and had the run of the zoo.

Today Moss and the zoo's technical staff are trying to fix the same hippo's "bedroom", after she and a lovestruck male hippo - divided by a thick wall - broke the gate.

"Of all the mammals, hippos are the biggest killers," he says. "They are more dangerous than sharks and lions. You can't get close to those guys."

His colleague, who does not want to be named, cuts in: "You have to love the animals - that's why you work at the zoo…of course there is a risk for zookeepers and animal attendants, but that adrenalin is what keeps us here."

"A dime a dozen" is a common phrase uttered by Moss and other zookeepers at the zoo. "We have impalas and springboks here at the zoo. They are beautiful, but they are a dime a dozen. Our five Lord Derby Elands [only 80 are left in the world] are definitely not a dime a dozen," says Moss.

The zoo runs several breeding programmes to help recover declining populations of species like the Lord Derby Elands. "The zoo is not just about conserving animals. We run breeding programmes in partnership with local and international zoos and swop animals to keep gene pools intact. We need to ensure that rare animals, especially, can be returned to the wild, where they belong," he says.

Zoo staff try to avoid interfering in nature. "We try not to hand-raise animals unless it is absolutely necessary," says Moss, pointing to a young lanky camel curled in its mother's lap. "We had to hand-rear that baby camel because her mom was old and weak. Generally, we find that mothers do a better job than we do."

For many of the zoo's lions, however, Cherry van der Walt, the large carnivore keeper, is "mom". Over the years she has raised many of them at her home on the zoo's breeding farm in Rietvlei, south of Johannesburg.

Her rottweilers have "adopted" the lion cubs and, unsurprisingly, van der Walt's two-year-old son's first word was "lion".

Like Moss, she spends her time checking on the zoo's lions, bears and other big cats. It's a job she is perfectly suited to. A troupe of lion cubs nuzzle her hand and chew playfully on her shoelaces.

"Lions have a healthy respect for those who raise them," she says. "They see you as their mom and remember you forever."

Zookeepers run enrichment programmes to mimic the natural behaviour of the animals in the wild and to stimulate them in captivity.

Says van der Walt: "I don't wash my hands after I have touched other animals so the lions can smell their scent. Or I put a pile of elephant dung in their enclosure and the lions wonder who's been in their territory. We give them toys and special balls in which we hide their food and they have to try get it out."

This is the sort of care many animals stuck in zoos in other parts of Africa do not get. Moss says most zoos on the rest of the continent are under-funded and in poor condition. Now he is setting up an association for African zookeepers - the first of its kind here - that will see zookeepers share ideas about taking care of different animal species.

"I guess I have always had a love for animals," says Moss. "And working with so many different animals - over 250 species - is really an incredible experience. It's great to treat them when they are sick, and look after them, and see an animal born here at the zoo."

He refers to Johannesburg Zoo as the city's green lung. "Just 2km away are the busiest roads in Johannesburg, but you wouldn't know it working here. It's so peaceful."

That sense of peace makes educating the zoo's visitors about the wonders of wildlife much easier.

"Most people come here for a chance to see wild animals. The huge majority can't afford to go to Kruger National Park. We pass on a really important conservation message."

Van der Walt agrees. "Here at the zoo people can observe animals in an unnatural environment, but that's for their education…we have the only two polar bears in Africa. Who will ever get a chance to go to Alaska to see polar bears in the wild?

"People are always complaining about the conditions of animals at the zoo. But the animals here live a life of luxury. When they are sick in the wild, they are ousted by their pride. Here, all their meals are given to them and they are surrounded by love," she says.

She adds habitat destruction, hunting and human encroachment are wiping out animals across the world. "There are only 500 Siberian Tigers left. Four hundred of these are in zoos around the world. It's up to us to take care of them and ensure they don't become extinct.

"If you speak to any zookeeper, he will tell you that he would love to see his animals in the wild. But the zoo is a place where we have compassion for the animals - who else will take care of them in future?"