Spring at the Prom

Driving through Wilsons Prom as the sun rises, I can’t help but feel incredibly lucky. Although dragging myself out of a warm cosy bed at 5am required considerable effort, it wasn’t for the spectacular sunrise. My true motivation is the knowledge that there are plump little mice waiting for me.

Sunrise at the Prom
The sun rises over Wilsons Promontory National Park

 

I’m headed to check my traps and see how the New Holland mice on Yanakie Isthmus are faring this month. Arriving at the sites just on sunrise, I walk along the traplines, clambering through the vegetation looking to see which traps have closed doors – indicating an occupant.

Peering into a trap, I pull out the warm fluff to see who has been lured in overnight by the scent of peanut butter, golden syrup, vanilla essence and oats.

New Holland mouse in a trap
A New Holland mouse (and its beloved peanut butter & oat ball) gets a rude early morning wakeup after I remove its warm fluffy bedding.

Discovering a New Holland mouse, I tip it into a bag and get to work weighing it, taking a genetic sample, and checking its gender, age, and reproductive status before releasing him and re-setting the trap.

A New Holland mouse huddles in a cloth handling-bag
A New Holland mouse huddles in a cloth handling-bag

Unconvinced that I’m actually a giant, terrifying predator, the New Holland mouse chooses to explore my lap before heading home to his burrow to sleep until nightfall. I quickly move on to the next trap, not wanting to keep the mice waiting any longer than necessary.

New Holland mouse on lap
Surprisingly chill, considering that I just snipped a tiny bit off his ear for a DNA sample

It’s breeding season for New Holland mice at the moment, and the next individual I encounter is playing her part well. Adult New Holland mice usually weigh about 18-20 grams at these sites. This little lady is a hefty 32g, soon to give birth to up to six babies. She will breastfeed them for the next month, until they’re ready to head out and find tasty seeds, leaves, invertebrates, and fungi to eat.

Pregnant mouse
One heavily pregnant New Holland mouse with engorged nipples

As the New Holland mouse breeding season can last 5-7 months, some of her kids from this litter will mature and have offspring of their own in the next few months. During that time, she will produce a few more litters herself.

Despite what may seem like quite high reproductive potential, New Holland mice are threatened and populations can disappear quickly. Breeding season length and success are highly dependent on resource availability – if there isn’t much food to go around, there will be fewer, smaller litters, with fewer of those offspring surviving to maturity.

Figuring out the specific factors driving population success will help us to protect and conserve the few populations of New Holland mice that remain in Victoria. A challenge definitely worthy of a 5am start.

New Holland mouse
A New Holland mouse wanders home through the prickly groundcover

NHMs head Off Track

unspecified
A New Holland mouse bounds home after release. Image: Ann Jones

The New Holland mouse population at Wilsons Promontory was lucky enough to have Ann Jones from Radio National’s Off track program come out and visit them recently. Ann also stopped by to chat with Jim Whelan, expert on all things Yanakie Isthmus, to learn more about the threat to NHMs and many other species posed by coastal tea tree encroachment. Listen to the experience and see some of Ann’s gorgeous photos hereAnd check out the video story here.

 

 

 

New Holland mice on camera

The New Holland mouse (Pseudomys novaehollandiae) is one of Victoria’s threatened native rodents. The charismatic little species has only been recorded from 3 areas across the state in the past 15 years (blue dots in map below) whereas historically it was recorded from 10, including metropolitan Melbourne (red dots in map below). That’s why I’ve embarked on a PhD to determine the status of NHMs across Victoria, and help protect this species from further decline.

New Holland mouse detection sites across Victoria. Red dots indicate sites in areas where the species has not been detected in at least 15 years, blue dots indicate areas with more recent detections. Dates show the range of years during which New Holland mice were known at each site.
New Holland mouse (Pseudomys novaehollandiae) detection sites across Victoria. Red dots indicate sites in areas where the species has not been detected in at least 15 years, blue dots indicate areas with more recent detections. Dates show the range of years during which New Holland mice were known at each site.

One of the greatest challenges for studying the status and conservation of New Holland mice (and many native Australian rodents) is that they can be very difficult to find; you can’t just see them in your binoculars or hear them calling in the bush. Adding to the challenge – many native rodents, including NHMs, go through natural periods where they persist in such low numbers that traditional survey efforts such as live trapping fail to detect them. New Holland Mice are also particularly fickle about their habitat preferences and may only persist locally for a few years before moving on, making their populations even more difficult to track.

New Holland mouse captured and released using live trapping. (Image: Phoebe Burns)
New Holland mouse (Pseudomys novaehollandiae) captured and released using live trapping. (Image: Phoebe Burns)

That’s why I’ve been trialling the use of cameras to detect the New Holland mouse. Traditional live trapping can be a great method for detecting a species in an area, and it’s critical if I want to know about health and reproduction, estimate abundance, or get DNA samples. However, sometimes when a species is at low densities it takes a huge amount of effort to be reasonably confident that the species isn’t there, which in a world of limited time and funding drastically reduces the area you can survey; a real challenge when a species moves in the landscape. This is where cameras can come in handy – you set them once and rather than having to come back every morning and afternoon to check each trap, you can just leave them in place for weeks at a time. The animals are attracted to a tasty lure (I like to use peanut butter, oats, golden syrup and vanilla essence) and while they investigate, the camera senses the heat and motion and snaps a photo.

Camera trap image of a New Holland mouse clinging to a bait station. (Image: Phoebe Burns)
Camera trap image of a New Holland mouse (Pseudomys novaehollandiae) clinging to a bait station. (Image: Phoebe Burns)

Cameras allow you to survey much wider areas, for longer periods of time with a fraction of the effort of live trapping – at least until you have to sift through the images and identify the animals. Once I know that NHMs are present in an area from the camera trapping, I can target those areas for live trapping to collect the rest of my data. My challenge, and the reason I did a camera trial, rather than just jumping straight into using cameras as a survey method, was identifying New Holland mice in the images.

Camera trap image of a New Holland mouse climbing on a bait station with a house mouse standing up against the base. (Image: Phoebe Burns)
Camera trap image of a New Holland mouse (Pseudomys novaehollandiae) climbing on a bait station with a house mouse (Mus musculus) standing up against the base. (Image: Phoebe Burns)

Rodents tend to look very similar on camera, particularly if the images are in black and white. It doesn’t help that New Holland mice are about the same size as the non-native house mice (Mus musculus); they can be hard for some people to tell apart when they are holding them in their hand. Since the house mouse has infiltrated all known New Holland mouse habitat in Victoria I needed to tell them apart from less than perfect images in colour and in black and white.

Camera trap image of a New Holland mouse clinging to a bait station. (Image: Phoebe Burns)
Infrared images of New Holland mice (Pseudomys novaehollandiae)(left) and house mice (Mus musculus)(right). (Images: Phoebe Burns)

Tens of thousands of images later, I can happily say that New Holland mice and house mice are distinguishable on both colour and black and white images. In the colour images the species can be distinguished by differences in colouration, but in black and white the distinction is all in the shape of the two rodents. New Holland mice have a much sturdier build, thick set neck and snubby nose, whereas house mice are much more slender with a pointed nose; sort of like the difference between rugby and footy players.

Now that I’ve got the IDs sorted, I’ll be using cameras (and live traps) to survey across Victoria and see where the New Holland mouse is persisting so that we can do our best to halt the species’ further decline.

Can you ID a New Holland mouse? Have a go with my quiz!

 

Originally published here