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Native Californian, biologist, wildlife conservation consultant, retired Smithsonian scientist, father of two daughters, grandfather of 4 small primates. INTJ. Believes nature is infinitely more interesting than shopping malls. Born 100 years too late.

Wednesday, December 12, 2012

A dirty filthy but princely rat

A bushy-tailed pack rat (Neotoma cinerea) in a pile of slabs in an abandoned saw mill (Flathead County, Montana).

They may be the best looking rats in North America, but it doesn't matter. In western Montana bushy-tailed wood rats are regarded as dirty filthy rats.

"How could such a princely rodent alienate so many?" I ask.

"Because they stink, they make a mess, and they crap and piss all over the place", Carl answers.

Carl's photos show the ugly truth happening on his front porch.

Bushy-tail caught during intimate moment
 of fecal assessment. (Photo by Carl Hansen)

A poop-obsessed pack rat seems to nuzzle and whisper tenderly to its fecal pellet.

Bushy-tail aids in the delivery of a fecal pellet
(photo by Carl Hansen)
And here you see the rat aiding the passage of a fecal pellet with the tender care of a midwife delivering a babe.

This may be an example of coprophagy -- recycling nutrients in the fermentation products of the caecum, but never mind.

Even David Attenborough's soothing zoological wonderment at such phenomena would not change the minds of the pack rat's detractors.

A pack rat midden in an abandoned cabin.
The beautiful furry rat has other unsavory habits -- like moving into human habitations and decorating with foliage, twigs, and anything else that strikes its fancy.

The middens become their toilets, glued together with urine and feces, and in due course the reeking mass solidifies, crystallizes, and becomes amberat, which acquires a resinous bouquet, and in fact was once mistaken for Native American peanut brittle by a gang of starving 49ers.

The pack rat however has redeeming qualities beyond its good looks and silky Chinchilla coat.

Scientists now know that this dirty filthy rat is an environmental historian.

Countless generations of pack rats have been contributing to some middens for at least the past 25,000 years.

These paleo-middens are monumental edifices hidden in rocky canyons and caves, and they contain a treasure trove on data on environmental change and its consequences on body size as an adaptation to heat dissipation.

The biologists quickly realized that fecal pellets in paleo-middens were not all the same size, and used Carbon 14 dating to assign ages to feces and associated plant parts.

They validated the relationship between pellet size and body size by examining several species of wood rats, and they did other tests to verify their findings.

Guess what?  Pack rats that lived 20,000 years ago in the shadows of the glaciers were impressive hulks.  They are estimated to have weighed as much as 450 grams (roughly a pound).

They grew smaller as temperatures increased after the last glacial, and by the mid-Holocene, about 6000 years ago they were 20% smaller than their ancestors.

It paid to be big, and even today the bushy-tailed wood rat is the largest living species of its clan.

The old pack rat may have a few nasty habits, but it's still a princely looking rodent.   

"Where is it? The viagra doesn't seem to be working".


Smith, F.A., J.L. Betancourt, and J.H. Brown. 1995. Evolution of body size in the woodrat over the past 25,000 years of climate change. Science, Vol. 270:2012-2014. 


Alyssa Johnson said...

One of my favorite posts of yours thus far. I agree, a regal looking rodent! But, I'm glad we don't have midden-making mice in NY.

Trailblazer said...

Great stuff as always, Codger! Your paleo-ecology comments regarding this species reminded me of Paul Martin's book Twilight of the Mammoths. A good read.

I've always wondered....are these midden sites something that you folks out west try to mostly avoid due to the threat of hanta-virus? Not sure what level of threat pack-rats pose, in that regard.

JK said...

"Chuckwalla Land" by David Raines Wallace also has some good tidbits and information on the paleomiddens. If I remember right he actually says the term "midden" applied to the amber-rat and not the structure and that only more recently has it become synonymous with the structure as a whole.

Really great images that show the bushy tail. Is there regional variance in how bushy the tail is? It might be the lack of good photos our our California bushy-tails, but I didn't remember their tail being quite so bushy.

If that last image was a cartoon in the New Yorker, you already won the caption contest. No sense in anyone else even trying.

Camera Trap Codger said...

Trailblazer: it's probably a good idea not play in wood rat middens in general. They host a lot of creepy crawlies, including hanta carrying mice of the genus Peromyscus. Wood rats are also hosts to infectious diseases.

JK: agree that we need to be careful in our use of the words. The codger doesn't condone the reckless substitution of one term for the other. Midden is the whole messy structure -- sticks, foliage, nests, and other objects including discrete lumps of amberat. Amberat is a solidified mass of fecal pellets and urine, and may contain other inclusions such as plant parts. It may be that very old middens are mainly and more or less uniform accumulations of amberat. At least that is what they look like in photos I have seen. BTW, one of my treasures is a lump of amberat given to me by RT. It is glassy and black and looks more like a product from a volcano than peanut brittle. Seeing a paleo-midden is on my bucket list.

Trailblazer said...

Makes perfect sense, Codge!

Even up here in the upper Midwest, when I walk into an old barn or shed with lots of rodent turds...I start getting a tad nervous (and we aren't particularly known for things like Hanta).

I can't even imagine what sorts of things one can pick up from a midden pile! A past mentor of mine was an aquatic animal health specialist...and picking through mammal intestines with him looking for various macro-parasites was always an eye-opening experience.

Made me realize, in general, how "unclean" we endotherms are :)

JK said...

I am with you and always thought midden referred to the entire structure. That is how I always used the word. Thanks for the clarification.

Meredith said...

Hello Codger! I am writing a short natural history article about N. cinerea for a local paper in Western Colorado. I need photos and I was wondering if the paper might publish one of yours. If you are interested please contact me at mbswett@gmail.com.
Thanks! Meredith