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The female northern hopping mouse is a hard-working little creature. Just 10 centimetres tall, it spends nearly a week digging a five-metre-deep burrow with secret exits. The burrows are such good hiding places that until recently the mouse had hardly been seen at all. Ann Jones reports.

If Kevin McLeod did a series called Furry Mammal Grand Designs, the northern hopping mouse would have to be the star of the first episode.

This tiny creature, only 10 centimetres tall, digs into the earth, creating up to five-metre-long tunnels for its thermally efficient house out of natural cement.

I would dream that I would see one running through the bush and be running after it, and then I’d wake up and I still hadn’t seen one

There are even more unexpected things about the endangered northern hopping mouse (Notomys aquilo), and many of them have been discovered by Rebecca Diete from the University of Queensland.

‘It’s quite cute, it stands up on its two hind legs like a little kangaroo, but it is a rodent, so it’s related to rats and mice. It has really big hind feet and a really long tail, big eyes and big ears,’ says Diete, who is probably not making quite enough fuss about how adorable the little mouse is.

‘From the tip of its nose to the base of its tail it’s about 10 centimetres. The tail is actually much longer than the body, it’s about one and a half times the length of the body.’

If an adult human had a tail of the same scale, it’d be nearly three metres long.

The tail is topped off by a lovely feather of sandy coloured fur which matches the animal’s back, though the mice may also have darker guard hairs over their glossy coat. This helps them to blend in with their choice of environment, whether sandy heath or grassland.

In this particular case, the sand is on an island off the coast of the Northern Territory.

The Dutch had a penchant for giving places literal names, so this place became Groote Eylandt, Dutch for ‘Large Island’.

If you look closely at the map, you might almost see the place that the island, with its tentacle-like peninsulas, cracked off the mainland at Arnhem Land and spun off into the Gulf of Carpentaria, leaving splinters of itself behind as a small archipelago.

It was this ancient separation from the mainland that is the salvation of Groote Eylandt’s modern wildlife. While there are wild dogs on the island, it has, so far, been spared from most feral herbivores, feral cats and cane toads.

It is a fascinating place full of cross-cultural history and also an exciting range of animals, some of which are very rare indeed. The island is a known breeding sire for roseate terns and the vulnerable hawksbill turtle, for example.

‘Groote Eylandt is the fourth largest in Australia,’ says Diete.

‘It’s got a mine on it, for manganese, from BHP Billiton, and they’re the ones that were funding my project. It’s also got two Indigenous communities.

‘The mine takes up maybe a sixth of the island, but the rest is fairly well untouched. A lot of the island has no tracks or anything at all,’ she says.

Diete would know—she has spent years scouring the island for signs of the mice.

Previously, northern hopping mice were counted via their spoil heaps—that is, the piles of sand left behind from their burrow diggings, and while Diete found heaps all over the place, she could not find any actual northern hopping mice.

She became a bit obsessed with figuring out why.

‘I would dream that I would see one running through the bush and be running after it, and then I’d wake up and I still hadn’t seen one.’

Perhaps it’s necessary give way to obsession a little bit in the context of this sort of ecology, because without perseverance, Diete may have given up and we still wouldn’t know much about the northern hopping mouse.

It took a whole year of searching before Diete captured an image of a mouse. It provided evidence that the vulnerable species was linked in some way to the spoil heaps.

Soon, Diete was recording hours worth of footage of the mouse’s construction activities. The footage, along with some radio tracking and trapping, has yielded groundbreaking findings.

First of all, it’s only the females that do the digging. Diete has found that they dig a sloping tunnel into the ground, pushing all the earth they excavate back out of the hole into a spoil heap.

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Whatsapp The northern hopping mouse measures around 10 centimetres from tip of its snout to base of its tail.

At some point, the female will decide that she has dug far enough and will seal off the working hole and replace it with a series of ‘pop holes’. These are smooth, well hidden holes the size of 50 cent pieces, often constructed out of small branches arranged off the original tunnel.

‘It’s the pop-holes that make the burrow so secure,’ says Diete.

‘I actually witnessed one night a snake entering into the burrow of my hopping mouse that had a radio collar on. I knew she was in there. The snake went down one hole, and my hopping mouse popped out another hole that I didn’t even know was there.’

The whole burrow will be between two and five metres long and reach a depth of around 45 centimetres. Remember, of course, that only one mouse digs it, and she is only 10 centimetres tall.

The spoil heap will end up being somewhere between 50 centimetres and a metre wide and the mouse will dig for five nights in a row.

There will be up to eight pop-holes as well, all well concealed, providing the mouse with escape routes to avoid predation.

If you’re worrying about the tunnel collapsing, don’t; female northern hopping mice have got that covered too.

‘They also tend to dig their burrows when the soil is still moist, so at the beginning and end of the wet season. Then once everything dries off it sort of its hold its shape, it’s quite baked into position,’ says Diete.

In its own way, the mouse creates a sort of concrete out of the sand.

All in all, it is quite a feat of engineering for someone so furry and powered only by seeds. It doesn’t end there, however.

Read more: Sydney's (aquatic) housing crisis

Back at the spoil heap, the work is not completed. The mouse will undertake a series of earthworks to cover her tracks and make it impossible to tell where the actual burrow is.

‘When I first started the project and I was seeing these spoil heap. I thought surely from the way that the animals dig the burrow that I would be able to tell which way the pop holes would be and it would make the pop holes easier to find.

‘I couldn’t work out why I couldn’t work it out, the spoil heaps looked fairly uniform.

‘When I finally was getting the camera trap footage, I realised that after they’ve closed off that tunnel, they’ll exit out of a pop hole, come back to the spoil heaps and spend a good 10 minutes or so just kicking the sand around.

‘That would make them quite conspicuous while they’re doing that, and so it’s obviously got a benefit for them by further disguising the burrow,’ says Diete.

The female northern hopping mouse has another nifty trick up her sleeve to help keep her safe from nosey neighbours who might eat her for dinner while she’s building her new house.

The mice keep an eye on the cycles of the moon.

‘I was only capturing them digging these new burrows around the new moon, so there wasn’t much light around, which would reduce the risk of predation,’ says Diete.

‘There are northern masked owls which would love a hopping mouse dinner and there’s northern quoll which would also take one if they had the opportunity.’

So what about the mystery of all the spoil heaps with no hopping mice?

Deite finally worked it out.

There is a tiny rodent, a quarter of the size of the northern hopping mouse and much more common, who has been building burrows in exactly the same manner: the delicate mouse.

The engineering mouse builds its dream house Listen to the full episode of Off Track to hear more about this clever house building mouse.

That means previous estimates of hopping mouse numbers made only from spoil heap assessments could be well out. The northern hopping mouse is already listed as endangered on the IUCN red list, so correct estimations of populations are imperative.

‘We need to be using better survey methods to start with, and really get a better idea of how many are on Groote Eylandt and also how many are left on the mainland,’ says Diete.

‘We shouldn’t be relying on signs of endangered animals if we’re not absolutely certain that it was them making them.

‘There were actually 10 species of hopping mouse in Australia and in the last 200 years we’ve lost five of them. So the genus is quite susceptible to threatening processes.

‘These mice fall into the category of what we call the critical weight range for Australian mammals. They’re small to medium, but not really small animals.

They seem to be more susceptible to threatening processes; introduced animals such as cats and the herbivores that might compete with them, but it’s also to do with changing their habitat; cutting down trees and altering the landscape.

Diete’s investigations on the island point towards the northern hopping-mouse having habitat preferences that are much more narrow than previously thought.

She is currently including her groundbreaking observations in a PhD at the University of Queensland, after spending a total of two and a half years doing field work on the island.

‘I actually didn’t want to do my PhD on a rodent,’ she says. ‘But this one really got under my skin, I fell in love with it.’

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