By the time Graeme Sawyer began tracking the yellow-spotted monitor, he had little reason to expect good news.

The large goanna (Varanus panoptes) was once abundant throughout the Top End, but like many native species, their lives were upended with the arrival of cane toads.

Researchers have tracked their shrinking populations, and the yellow-spotted monitor's status is now listed as vulnerable in the Northern Territory.

"They basically see the cane toad as a big juicy frog and die from it," said Mr Sawyer, the head of Biodiversity Watch.

"There's a whole bunch of our reptiles that have been hammered pretty hard — these guys probably the worst.

"That's why we've been surprised there's such a large number of them hanging here."

A team of volunteers has been laying and checking the traps for several years. ( ABC Radio Darwin: Jesse Thompson )

A colony of 50

Within a densely vegetated patch of habitat behind a university and bordered by Darwin's northern suburbs, the goanna could be staging an against-the-odds survival story.

Four years ago, Mr Sawyer and a group of volunteers began monitoring the patch, routinely dropping raw chicken necks into one-way cages throughout the bushland to see what was there.

They have been mystified by a surviving colony of at least 50 goannas mere suburbs from where others have died.

"What's surprising is from the beach car park all the way out to Lee Point [a large coastal area], we've got nothing," Mr Sawyer said.

"So it's just this pocket here of survival, and we really aren't sure why that is."

It's also a tenuous survival — just last year, Mr Sawyer found dead goannas in the area with toads nearby.

Another nearby colony showed promise then died off; there's no scientific proof, but the deaths correlated with a spike in the cane toad population.

This dead goanna was found near a cane toad it presumably tried to eat. ( Supplied: Graeme Sawyer )

But their survival here posed a mystery that ecologists said was worth investigating.

"These peri-urban areas in spaces and towns that wildlife can persist in are becoming increasingly important," Mr Sawyer said.

"I think it's important we understand how the wildlife are going in those spaces."

Volunteers have checked the traps three times this year, around the time the goannas shake their avoidance instincts and be drawn in by the stench of raw meat.

They are hoping some of the creatures will arrive soon because none were seen during the most recent check — but there were more than 30 cane toads.

Cane toads here to stay

The report from a senate inquiry into controlling the spread of cane toads was handed down this week and contained little good news.

The pests are likely here to stay, they're capable of spreading faster than previous estimates (55km per year), and the economic impacts of their movement are uncalculated but likely to be enormous.

Mr Sawyer checks six traps on the fringe of a vegetated area. ( ABC Radio Darwin: Jesse Thompson )

A submission from the NT Department of Environment and Natural Resources said cane toads were unable to be managed once established.

The department said the focus should be on keeping offshore islands and areas with high conservation value toad-free.

But Mr Sawyer said with regards to the monitor, its best shot at survival would be to actively suppress the toad population to slow its spread into areas cohabited by vulnerable and threatened native species.

"I can't see why we're not doing that with toads, at least in some particularly identified places where you might get quolls or you might get goannas persisting," he said.

"An area like this, with a little bit of management, would make a huge difference."

Little funding

Why the goannas have survived could come down whether there's not enough nearby fresh water to sustain cane toads, or that the area is so rich with other food the goannas don't eat them.

"What I would love to think is that our animals that are persisting here are able to eat them and survive, but we haven't got any evidence of that," Mr Sawyer said.

The delicate ecological balance raises other questions about the population dynamics, whether goanna numbers are plateauing, and whether they commute to urban areas for food.

Fifty goannas have been microchipped in the area. ( ABC Radio Darwin: Jesse Thompson )

Then, there is the funding hurdle for the conservation group.

"Unfortunately, because we don't have any budget for this stuff, we don't have any tracking gear," Mr Sawyer said.

As well as the cages, the volunteers are relying on anecdotal sightings to track goanna numbers.

Mr Sawyer had previously painted numbers on them in the hope that people would find it before the skin was shed.

It was a method of finding out the damage bill on a pillar of the local ecosystem, he said.

"They're actually one of the key animals that help manage the way ecosystems develop and form, so in that sense they'd be a keystone predator.

"We haven't done the research to know what happens with panoptes out of places, but one thing I think we can safely assume is it's not good for the whole ecosystem to have its predators gone."