Wednesday, June 20, 2007

Norway Rats vs. Roof Rats

Pest rats in California come in two varieties - Roof and Norway. Around my house, they are 'dead' and 'deader'

I was recently skimming through some of my old kill't rat photos when something that had been in the back of my mind for a while finally took shape.

After spending more time looking at the photos and doing a bit of web research, I now think that the rats I had been identifying as 'adult' Roof rats (Rattus rattus) are actually Norway rats (Rattus norvegicus). Have a look at the following side-by-sides and see if you agree that these are two different species: the first is the one I now believe is a Norway, the second I still think is a Roof. The most commonly-referenced distinguishing characteristic is the tail. The tail of the Roof rat is longer than the body and head combined, while the Norway rat's tail is shorter than the body plus head.

Norway Rat?

Note the long body and lighter color. The tail seems on the long-side for a Norway, but is likely just short of the length of the body+head

In the mug shot, you can see the smaller, "Norwegian" ear-to-head ratio

Roof rat?

Smaller overall, longer tail than head+body, more grayish color

The ear (what's left of it) is larger in proportion to the head

I had always thought it strange that the coloring was so much lighter and browner on the big'uns, but just chalked it up to variation. Plus, I had read somewhere a while ago that Norways and Roof rats tended not to be found sharing the same territory (see quote below). And since I knew I definitely had Roof rats -- they are very agile climbers and have been seen (and shot) in my tree -- I assumed that they were the only ones I had.

Basically, I did a lot of assuming -- and I know what happens when I assume.

Have a look at the details/specs on the following site (Anne's Rat Page). Heck, while you're there, take the quiz:

As mentioned, Roof rats (a.k.a., black rats, ship rats) are excellent climbers, often living in nests above ground. Norway rats (a.k.a., brown rats, sewer rats) more often tend to be burrowers. Regarding overlapping populations, I found this quote on the Internet (source is unclear):

"The present distribution of the Norway and roof rats appears related to two factors, competition between the two species and the reaction of both to different climates. When the aggressive Norway rat and the roof rat compete for the same areas, the Norway rat frequently becomes dominant, and the roof rat soon disappears. Only under special conditions do both species live in the same area. In one eastern seaport, roof rats live in the top of grain elevators and Norway rats live in the bottom. This is probably because roof rats are better climbers than Norways. It is generally only in such situations as these that roof rats are found living in Norway rat territory."

So based on my new assumptions, I now see my backyard as a melting pot of rodentia, where rats of all races and creeds come to live. It's my job to welcome each and every one of them with a .20 caliber handshake.


JP said...

Hey, got your link from Pyramydair blog: BB linked it to you as a "regular", and something of a [promising] up and coming shooter I think. Anyway, I'm not too good at species I.D. except for "Food", "food in an emergency", "Pest", and your definition of rats: dead and deader. Anyway, keep plinking and I'll be waiting for part 3 of the original story BB linked us to. JP

Kodiak said...

Hey, that's great. It's an honor to have visitors from the Pyramydair Blog which I am a huge fan of and certainly obliged to for all it has taught me. It was a surprise to me to see a sudden influx of new readers, but now I know where they're coming from. So let me say, Welcome!
Yeah, it's funny, I still can't say with 100% certainty that these are two different species. My instinct tells me they are different, but I'd love to hear from an expert.
I'm currently writing part 3 of the Humble Origins series, so keep checking back -- it will be up and ready soon.

Anonymous said...

Thanks for the nice pictures of the two rats. That will make it easy to identify after the snap. By the way, rats are not parasitic although they do probably have parasites on them.

Kodiak said...

I use 'Parasitic' in the sense that they thrive off the leavings, by-products and habitats of humans. Much of their success is based on reliance on us. Without humans, rats would exist in a small fraction of the numbers they do today.

Anonymous said...

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Kodiak said...

Thanks for stopping by and for taking the time to leave comments.

Glad folks are finding the blog useful and/or entertaining!