Mastacomys fuscus

Broad-toothed Rat at Charlotte Pass, NSW

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Identification history

Mastacomys fuscus	16 Mar 2023	DonFletcher
Rattus rattus	14 Mar 2023	CarbonAI
Mastacomys fuscus	14 Mar 2023	MLH

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User's notes

Single recently deceased individual in snow gum woodland

10 comments

MLH wrote:

14 Mar 2023

Carbon AI has not got this right.

DonFletcher wrote:

14 Mar 2023

Hi @BelindaWilson, Hi @ChrisM, Hi @WillO,
This is clearly not Rattus rattus and it is also not Rattus lutreolus but, not being familiar with Mastacomys fuscus, I'm not 100% sure I should rule out Rattus fuscipes. Things that make me like M. fuscus for this are: tail shorter than HB, ears almost covered by cheek hair, and hunched appearance, but there are problems. Three things that argue against ID as M. fuscus are: (i) lack of flecking in the fur, (ii) colour of feet seems more like R. fuscipes (brown with a pinkish tinge) than M. fuscus (dusky brown above and below according to Menkhorst et al), and (iii) tail is not coloured 'uniformly brown only slightly paler below' but is pretty well a classic R. fuscipes tail colour. I'm inclined to go with Mastacomys fuscus, but would appreciate your opinions.

MLH wrote:

14 Mar 2023

Note that the habitat is classic M. fuscus - above the snowline and in dense understorey with mix of forbs, grasses and shrubs

DonFletcher wrote:

14 Mar 2023

Hi MLH, many thanks for these photos. Small mammals are hard to ID from photos. For future reference, the guidelines at the beginning of the section may help, as follows:

Tips to increase the potential for correct identification:
An image that is sharp, not blurry;
A scale;
A view of the whole animal (preferably stretched out if it is a carcass);
Views of every surface - (not always possible but ideally this includes a profile of the head, good views of the ears, the belly, the pads on the hind feet, and a good view of the fur and skin on the tail from below and above);
Views of the teeth; and
A count of the number of teats.

DonFletcher wrote:

14 Mar 2023

Hi MLH, in the area, did you see tunnel-like runways in the grass with numerous rat-sized droppings containing grass fragments?

MLH wrote:

15 Mar 2023

I looked for the tunnels afterwards but didn't see any obvious signs in the area. The immediate vicinity was more shrubby than grasses and thus less likely on cursory glance to contain obvious tunnel like structures. No scats apparent on the entire walk. I snapped the pictures quickly on the return section of the walk and I thought I was probably not capturing the diagnostic features (Like tufts of hair in the ears according to this site https://www.swifft.net.au/cb_pages/sp_broad-toothed_rat.php) In the two hours between walking out and back the maggots got going so I wasn't keen to examine the teeth too closely. Although I had nothing to scale it against it was quite large.... as big as an adult Rattus norvegicus.

DonFletcher wrote:

15 Mar 2023

Will has referred this on to two other Mastacomys gurus, Linda Broom and Ken Green. We await their verdicts.

BelindaWilson wrote:

16 Mar 2023

Hi Don and MLH, I have referred the record for Kiarrah Smith and she said: "Definitely not R. rattus, as Don said, though if it were a Rattus, it'd be R. lutreolus. I would lean toward M. fuscus too, though I'm not terribly familiar with the species - from what you can see of the feet and tail (though blurry), it doesn't look like a Rattus."

DonFletcher wrote:

16 Mar 2023

Thanks Belinda and Kiarrah.

DonFletcher wrote:

16 Mar 2023

I just saved these pics to where I can see them on a better computer monitor. Two things i had not considered before were the tail being SLIGHTLY paler below, and the poor view of the foot pads that can be got from the 3rd picture. Together with Kiarrah's comment, its enough for me to confirm Mastacomys. But if Ken Green and Linda Groom disagree we can change it. cheers

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