Identifying garden murids: a case study in unfortunate naming

It's a bit dull, spending all day revising. I have a window which looks over the garden, but being a shared rental house it's not a very nice garden. It's mostly slabs and concrete, with a shed at the end and a strip of grass the dog uses to relieve himself. So the wildlife highlight is usually a pigeon. But not today!

A short while ago, I saw movement in front of the shed, too bouncy for a bird but sort of heavy for a leaf. I put my glasses on and glimpsed what looked like the most adorable baby rat as it bounded behind some junk. I've seen baby rats before, and I'm really not usually a mammal fan but they were just lovely. I think I have a soft spot for rats.

I caught sight of it again a few minutes later, snuffling around in the grass. I was surprised. Looking again, it had very mousy proportions, even for a juvenile. It was the right brownish colour for a mouse. But its body must have been a good ten centimetres long. Could this be a gigantic mouse species I'd never heard of? Or even a mutant metropolitan variety terrorising Londoners? It definitely didn't look like a rat.

This is a house mouse (all British mice have pretty much the same shape):

Source: https://commons.wikimedia.org/wiki/File:%D0%9C%D1%8B%D1%88%D1%8C_2.jpg

And this is a brown rat:

Source: https://www.flickr.com/photos/jean-jacquesboujot/9874371664

As well as being much bigger, brown rats have proportionally smaller heads, ears and eyes. Basically the more adorable, the more likely it is to be a mouse. This rodent in the garden was definitely on the mouse end of adorable.

So I got on the Internet and searched for mouse species in the UK. They really do all look quite similar, and the biggest (the yellow-necked1) only gets to about ten centimetres in total length. About half of that is tail. So it really shouldn't have been a mouse.

Then I thought of the black rat. They are smaller than brown, but were more or less wiped out centuries ago when the brown rats came in. And surely black rats are, like, black? But apparently there are brown colour morphs, and they are slowly regaining a foothold on this island2.

So could it have been a brown black rat? I think so. This is a black rat:

Source: https://www.flickr.com/photos/alexfiles/3872887266

Sure looks brown and mousy and adorable enough.

Rats and mice belong to the family Muridae. It seems to suffer from a bit of a naming problem.

• Black rats are not always black.
• Brown rats, Rattus norvegicus, didn't actually get to Norway until after being named after it3.
• Yellow-necked mice are distinguished from the very similar field mice by a yellow collar. 'Yellow' is really quite a stretch.

Source: https://www.woodlandtrust.org.uk/blogs/woodland-trust/2016/10/types-of-uk-mice/

• And finally, though not a murid and actually part of the squirrel group, surely edible dormice aren't really edible. Who could possibly eat a dormouse honestly

Source: https://pixabay.com/en/edible-dormouse-sleep-furry-sweet-1179703/

(Thus concludes probably the only post on furry mammals ever. Back to the interesting tetrapods next time.)

References
1 https://en.wikipedia.org/wiki/Yellow-necked_mouse
2 "The black rat, Rattus rattus, is believed to have made a comeback in the UK after one was found under a woman's fridge in Cornwall." http://news.bbc.co.uk/1/hi/uk/337680.stm 
3 https://en.wikipedia.org/wiki/Brown_rat#Naming_and_etymology