Almost 70 years after settlers arrived in Wajuk country — the place we now know as Perth —they were still making efforts to make it feel like home.

They formed a group, the Western Australian Acclimatisation Committee, which was charged with making the colonial environment more amenable to the settlers.

They tried to introduce an impressive number of animals — Murray cod, eels, white swans, peeking nightingales, goldfinches, ostriches, angora goats, Gippsland perch, salmon, quail, pheasants, rainbow trout and kookaburras from the East Coast.

There was even a release of deer, a gift from the royal family, into the state's south-east.

Not all of the animals managed to survive, let alone thrive, but after escaping from the Perth Zoological Gardens, palm squirrels managed both.

Survival of the fittest

Also called the palm squirrel, it's no bigger than a rat, but it has a bushy tail which is often carried aloft, curled into a question mark or straightened in exclamation.

It's active during the day, and eats seeds and leaves throughout the year and fruits and insects whenever it can.

Even while confined to the Perth zoo, palm squirrels faced some serious dangers.

In 1941, a reporter for the Daily News in WA wrote:

"Every now and then they skim recklessly up and down the iron bars of the cages of unfriendly animals. This innocent and playful act is often their last. One moment they are scurrying nimbly roofwards and the next a monkey's hairy, muscular arm shoots forward. Quick as they are, many are dragged inside to be devoured. Monkeys on the whole are bloodthirsty. If they are given a piece of meat, they will reject it in disgust; it has to be killed by their own hand to be acceptable. Leopards also take part in the slaughter of unwary squirrels. Survival of the fittest is the law under which the squirrels live."

In 1972, an honours student studying the squirrels found those inside the zoo were being eaten by captive hawks and brolgas, while those on the outside had to deal with rats, cats and Nankeen night-herons.

If that wasn't bad enough, seasonal changes in diet were having a major impact on the rodents.

In the 70s, at nearby Como High School, the palm squirrel population remained strong during term. But when holidays kicked in and the kids took their banana skins and sandwich crusts to the beach, numbers dropped.

There simply was not enough food to support them all.

The shy and diurnal palm squirrel is considered an invasive species and potential pest. ( Flickr: Olivier, CC BY-NC-ND 2.0 )

But they persisted in the area around the zoo, and radiated slowly outwards, initially into the adjacent golf course then onto suburbs.

The population peaked at about 1,000, according to Lindsay Strange, a biosecurity officer with the WA Department of Food and Agriculture.

"As a department we had an exclusion zone that we set up — basically a 30-square-kilometre area around the zoo — and said, 'OK, we know they're in there and they're not doing a lot of harm, we'll keep them in that exclusion zone.'"

The squirrels, however, kept turning up further afield. One was sighted a stunning 160 kilometres out of Perth in the wheat belt town of Pingelly, having hitched a ride in the roof of a transportable house.

A high-risk species

Despite its adorable appearance and apparently benign presence in the inner suburbs of Perth, the palm squirrels are an invasive species and constitute a danger to the environment.

The Queensland Department of Agriculture and Fisheries reported that Indian palm squirrels were a high-risk species, with major pest potential in Queensland, the Northern Territory and northern WA due to favourable weather conditions.

They could have a major impact on fruit and nut production, and Brisbane would offer them ideal conditions.

In response to the northern Australia-wide threat, the WA Department of Agriculture swung into action with a pest control program.

"Believe it or not, out of all the invasive species I've dealt with, they're one of the easier ones to trap. They trap really easily and they come to a feed source really easily," says Mr Strange.

"They just love peanut butter."

Following the trapping efforts of the last three years, Mr Strange believes there are now fewer than 10 squirrels left in Perth.

If you see a palm squirrel in Western Australia, please contact the Department of Agriculture's Pest and Disease Information Service on 1800 084 881.