The dog stopped abruptly in front of a small bush and lay down, signalling a find as Delta's handler moved in to search the surrounding area.

Hidden in the tall grass was a tiny reptile, its shell marked with yellow star-like patterns -- a clear sign it was a geometric tortoise, a species found only at the southern tip of Africa.

"It's an adult female, you can tell by its flat belly," said Esther Matthew, the dog's handler and a conservation officer for South Africa's Endangered Wildlife Trust.

She explained that the organisation uses canines to sniff out the endangered species by "building positive association with the tortoises' odour", throwing Delta a foam frisbee as a reward.

Dogs are five times more effective than humans at this type of search and "also help us find the smaller tortoises which are often overlooked, the hatchlings and the juveniles", Matthew said.

"We've seen a dramatic increase in the number of finds with the dogs."

- Shrinking numbers -

The help has become crucial in studying and protecting the geometric tortoise, found only in South Africa's Western Cape province and on the verge of extinction.

The species' population was already as low as 1,500 individuals in the wild in the early 1990s, according to biologist Andrew Turner, who works for the conservation authority Cape Nature.

It is now estimated at only several hundred animals with "declines pretty much across the entire remaining range of this species", he told AFP.

On the nature reserve, Delta and Matthew -- helped by colleagues searching the bushes with sticks -- found a dozen of the hardy reptiles.

"We record all the tortoises we can find, all the data, measurements and weight," Delta's handler explained.

- 'Creating corridors' -

With the species' natural habitat shrinking due to agriculture and urban expansion, these surveys have become all the more critical, Turner said.

"There are very few places left in the Western Cape that still support these tortoises. It's really just a couple of nature reserves and pieces of good habitat left on people's private property," he added.

"The remaining patches of vegetation are not really connected to each other anymore. There are farmlands in between, roads, towns and industries so there is limited ability for the tortoises to disperse and rescue other populations."

This fragmentation makes them all the more vulnerable to droughts, predation and fires, which scientists argue have become more frequent and intense thanks to climate change.

Poaching -- of the tortoises and the plants they feed on -- is also a threat, Turner said.

"They are down to such small levels that they actually need as much assistance as they can get," he said.

To save the species, the Endangered Wildlife Trust has looked at building "partnerships" with landowners and communities living in the animals' habitat.

"The biggest thing is... creating corridors where species can work through," explained Zanne Brink, who leads the organisation's dry lands conservation programme.

"Our biggest challenge is to get enough information to prevent critical biodiversity areas from being lost to unsustainable land use."