The New Holland mouse

Author
by Phoebe Burns
Publish date
31 July 2015
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The New Holland mouse (Pseudomys novaehollandiae) is one of Victoria’s threatened native rodents. The charismatic little species has only been recorded in three areas across the state in the past 15 years (the blue dots in the map below), whereas historically it was recorded in ten, including metropolitan Melbourne (the red dots in the map below). That’s why I embarked upon a PhD to determine the status of NHMs across Victoria and help protect this species from further decline.

New Holland mouse detection sites 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.

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 with your binoculars or hear them calling in the bush. Many native rodents, including NHMs, go through natural periods where they persist in such low numbers that traditional survey efforts 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 New Holland mouse 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. This is a real challenge when your 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.

New Holland mouse Camera trap image of a New Holland mouse 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 all 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.

New Holland mouse and house mouse 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
 

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.

New Holland mice and house mice Infrared camera trap images of New Holland mice (left) and house mice (right) investigating bait stations.
Image: Phoebe Burns
 

Tens of thousands of images later, I can happily say that New Holland mice and house mice are distinguishable from one another in 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, a thickset neck and a snubby nose, whereas house mice are much more slender, with a pointed nose. It's not unlike 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.

You can follow my PhD progress and fieldwork on Twitter and at my website to stay up to date with the status of New Holland mice as I search for them throughout Victoria.

Additionally, you can try your hand at identifying New Holland mice in my New Holland mouse quiz.

Comments (3)

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Damian 5 August, 2015 06:23
I once rescued one of these little guys from my laundry when I lived in Point Roadknight. I knew it wasn't a normal mouse! He or she was promptly liberated into the yard. That would have been in the late 90's, so unfortunately that dot on the map will have to stay red I think.
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Jason Pickering 17 November, 2015 16:31
I think i found an infant NHM at Sealers Cove on the 25th of Oct this year. We manage to take a couple of photos (not the best quality) before we found his worried mother off to the side of the trail. Didn't manage to get a snap of her though. The mother definitely had the thicker head. Never seen anything like it before.
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Nina Kaluzza 14 July, 2016 12:32
Hi Phoebe, what amazing work you are doing to conserve this wonderful rodent! I would like to get in contact with you to discuss your findings, as like you, I am completing my RHD on a rare and vulnerable muridae here in SE Queensland and my research has provided great insight on behavior, adverse effects and distribution. If you get the time, (ha) it would be nice to chat to the like minded.
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