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blue smurf pee, rabbits, and buckthorn

This past week I participated in one of several Christmas Bird Counts that I do annually. I’ve done counts here in Michigan on sunny, cloudy, snowy, rainy, raw, and balmy days, but never on a day that included all of the above, plus thunder, lightning, and a rainbow (all with the temperature under 40 degree F). Very strange.

We had a nice diversity of species, including a Gray Catbird, which is pretty rare in winter around here.  It was camping out in a buckthorn tree, which harbor about the only berries left at this point (fruit being the main food of a winter catbird in these parts).  This brings us to the most unusual sighting of the day.

As we tromped through the woods, we came across a bright blue stain in the snow, as if someone had spilled windshield washer fluid.  A rabbit turd was next to it.  We thought this was weird, but figured there must have been some litter that had leached blue ink beneath the snow, and that the rabbit poop was coincidental.  Then we found another identical stain and turd.  And another.  I quit counting after twenty or so.  Not every pile of bunny pellets had a blue stain, but all blue stains had some poop. Obviously, this was rabbit urine. As usual, we were in an urban area, next door to a chemical plant, in fact. Was there a family of toxic rabbits running around, voiding blue pee?

I came to learn that this neon cerulean tinkle is a result of rabbits consuming buckthorn (Rhamnus cathartica), a highly invasive tree in North America.  One of the chemical constituents is excreted in the urine, and within a short time turns blue when exposed to sunlight.

The only credible mention of this was an anecdotal account on the Ontario Woodlot Association web site. The author observed this blue pee and experimented by feeding domestic rabbits and goats buckthorn and other shrubs.  Blue pee resulted only after buckthorn consumption. Blue urine has not escaped the notice of other folks, but nearly all other explanations I found on the Internet were remarkably asinine, including people spitting out mouthwash (I know I often take advantage of a nice stroll in the woods to bust out the Listerine) and Bigfoot piss.

Because buckthorn is such an important invasive species and so common in urban areas, I am especially interested in the often unexpected ways it impacts other organisms (like the ecosystem-altering way it interacts with non-native earthworms). I have done quite a bit of research on buckthorn, but mostly as it relates to birds consuming the fruits, not mammals eating bark and shoots.  I did a literature search, and found nothing on this phenomena, which must, of course, occur in the native Eurasian range of buckthorn as well.

I’m surprised that I’ve not found blue urine stains at my own study site, which is jammed with buckthorn and has no shortage of rabbits.  I figure it must have to do with the fact that buckthorn is not a preferred forage for mammals (due to the many phytochemicals it contains, one of which apparently causes this phenomena).  If the rabbits aren’t eating it, they aren’t peeing it. It’s also possible that not all rabbits would void blue urine after eating buckthorn.  Perhaps only certain individuals are unable to metabolize some chemical constituent. Or the reaction may require consumption of a certain amount, or the combination of buckthorn and some other food.

I’d be really interested in any research results on this, if anybody has some references.

Filed in Natural history

Comments on this entry are closed.

  • Lanny December 30, 2005, 2:41 pm

    Where else could we learn about stuff like this? Nuthatch, your curiosity is amazing and quite wonderful.

    You reminded me of a biology grad student into whose hand I'd set a freshly-banded hummingbird to release. Upon launch, it left a little "present" in his palm (a common occurrance). Fascinated, he wondered what it would taste like…so he tasted. "Well?" said I. "Not much flavor, just a little sour." I verified that hummer pee is mainly water, with a dash of uric acid. I wonder what the subject of his dissertation will be?

  • Nuthatch December 30, 2005, 2:46 pm

    Thank you. Not only am I always curious about invasive species and ecological interactions, I have never lost my juvenile fascination with poop and pee. Sometimes it all collides, and the result is a post like this!

  • TroutGrrrl December 30, 2005, 5:50 pm

    This is why I visit here….

  • pohanginapete December 30, 2005, 8:07 pm

    If my pee turned blue on exposure to sunlight, I'd be worried (to put it mildly). Not much to worry about, though — on hearing my opinions, most people reckon I'm pissing in the dark ;^).

  • Pamela December 30, 2005, 10:06 pm

    I've heard of this before–never seen it myself. I enjoyed the photo–that's some blue! I too am a fan of spoor–poop and pee are among my favourites. Thanks too for the Bigfoot forum link. I had no idea….

  • Cindy December 30, 2005, 11:35 pm

    your gift of finding the uncanny is trully amazing.. and that comes from an insatiable curiosity that only few possess. Your posts never cease to teach and delight me.
    Happy New Year !!

  • Roger B. December 31, 2005, 9:07 am

    Fascinating observations. In our neck of the woods Buckthorn (aka 'Purging Buckthorn') is a scarce but indigenous species. It's most notable for being the main foodplant of the Brimstone butterfly (Gonepteryx rhamni)

    Any idea which part of the plant the bunnies had been eating? Leaves? Berries? Bark?

  • Happy and Blue December 31, 2005, 10:13 am

    Maybe you just found the Easter bunnies hideout. If it can lay fancy chocolate eggs maybe it can pee in various colors.
    Or it could be what it's eating I guess. Who really knows..
    Anyways, got here from Rurality.
    Hope you have a very Happy New Year..

  • Jenn December 31, 2005, 8:22 pm

    Couldn't find anything about this aspect of Rhamnus in my library. A very interesting post. Love the new blog topper!

  • Fragments From Floyd January 3, 2006, 5:11 am

    That’s Why They Call it Work

    There was supposed to be an image (remember when there were pictures on Fragments?) but due to technical hairballs left over from the last resussitation of the MT circuitry, I can’t post images. Our technical wizards are working on it….

  • Aydin January 4, 2006, 5:48 pm

    Manual trackback:

    Your blog is not accepting trackback pings. I got tired of waiting.

  • Deb January 5, 2006, 2:07 pm

    I have to laugh at this one…it just so happens that last winter I was finding strange blue stains in the snow around our house, and I was looking for a natural explanation. A few days later I noticed the bottle of blue mint Listerine sitting out on top of our pump house. We are living in the Dark Ages of no indoor plumbing, and the culprit was in fact my husband's outdoor oral hygiene. But blue bunny pee sounds like a much more fun explanation!

  • Nuthatch January 5, 2006, 2:27 pm

    So long as your husband wasn't also depositing a rabbit turd in the stain, all is well.

  • Abnormal Interests January 6, 2006, 10:43 pm

    Friday Snow Blogging

    The other day Aydin Örstan directed us to Blue Snow and Red Snow and showed us his own yellow snow. Well not exactly his own yellow snow but some yellow snow near his home. And while Aydin’s snow is now…

  • Steffanie March 11, 2007, 11:37 pm

    Boy I sure am glad I was shown this link, I just encountered "blue stains in the snow along with lots of rabbit turds" in my horse pasture and just outside of it as well. At first I thought someone was trying to poison my horses with windshield fluid, but after coming across this study I am just overwhelmed with relief that it really is the rabbits urine! Scary but interesting!