Understanding more about the behaviour of urban rats will help with better planning for Predator-Free 2050 and the goal of eliminating rats, stoats and possums from New Zealand.

Photo: RNZ / Alison Ballance

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Victoria University of Wellington student Henry Mackenzie jokes that by the end of this year he will be keeping “rat hours.”

That’s because rats are active from dusk until dawn, meaning Henry is out and about for most of the night as he radio-tracks rats in various Wellington suburbs to work out how large their home ranges are.

Photo: Stephen Hartley / VUW

Henry’s project is part of a nationwide study called People, Cities and Nature, which is carrying out research to assist with ecological urban restoration.

Researcher Stephen Hartley says that very little is known about the behaviour of urban rats as most research has been carried out in natural environments such as the bush or on islands.

Photo: Stephen Hartley / VUW

Step one for Henry involves setting live capture traps in the back gardens of local residents to catch rats. Henry says he has mostly caught ship rats, although he is also tracking a couple of Norway rats.

Wellington Zoo vet Craig Pritchard helps anaesthetise the rats so that Henry can fit them with a small collar carrying a radio tracking device.

Photo: Stephen Hartley / VUW

Henry also marks each rat with platinum blonde hair dye to create a unique pattern of marks that will show up on infrared motion-activated trail cameras.

Photo: Stephen Hartley / VUW

Henry has ten radio-collared rats that he is following in the inner-city Wellington suburb of Wellington.

He is also tracking rats in Brooklyn and Te Aro.

Henry has radio tracked during the daytime, to find out where the rats are nesting. Ship rats are arboreal and create untidy sparrow-like nests from twigs and branches high up in trees.

Ship rats are also known as roof rats, and frequently make themselves at home in the walls and roof spaces of houses.

Norway rats burrow, which makes it much harder to locate them as the radio signal gets blocked.

Photo: RNZ / Alison Ballance

It is early days for Henry’s study, but he is beginning to build a picture of the nocturnal activities of different rats.

In one garden, he is following three ship rats whose ranges overlap with one another.

The longest distance that a single ship rat has moved in one night is 30 metres, whereas another Norway rat is always found either in or immediately next to a compost bin.

Once Henry has completed the radio tracking he will plot his data to calculate the size of home range for each rat.

This information will be useful for projects such as Predator-Free Wellington, which is currently spacing bait stations at 50-metre intervals. In an urban eradication project the aim is to have bait stations close enough that every rat has a chance of encountering one, whilst minimising how many are needed.

Our Changing World will be finding out about Predator-Free Miramar and Predator-Free Wellington in next week’s show.

Find out more about predator-free efforts in New Zealand & urban restoration

Detector Gadget the conservation dog is a rodent detector dog.

Restoring Fiordland’s island lifeboats is an ambitious programme to get rid of rats, stoats and deer from many Fiordland islands.

Predator-Free New Zealand: dream or reality -a panel of experts discuss whether New Zealand can be predator-free by 2050.

Science of a mega-mast & planning wide-scale predator control – how we knew in advance that 2019 would see a rat & stoat plague following a mass seeding event, and how the Department of Conservation plans to respond.

Chemical camouflage - putting predators off the scent.

Predator-free in the city – predator-trapping in Wellington’s Polhill Reserve.

Urban restoration in Hamilton