Blue Snow Mystery Solved, Rabbits and Buckthorn

It seems the blue snow I saw in the woods a few days ago most likely comes from a rabbit who ate Buckthorn twigs or bark.

Denise sent me a link to a blog post from Bootstrap Analysis describing just what I saw with a photo similar to mine.  The author of the piece (whose name I couldn’t find) wrote:

“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.”

And from The Ontario Woodlot Frederick W. Schueler writes.…

“The urine of domestic buckthorn eaters is initially yellow or brown, but within ten minutes of exposure to sunlight turns bright blue in the snow or on paper. I’d been watching for rabbit-browsing of buckthorn since the winter of 1998﷓99, and the blue spots occurred the only time I saw them eating buckthorn, mostly very fine twigs from sprout clumps where I’d cut the original stems to control the invader.”

We have lots of what I believe is  Alder Buckthorn growing in the marsh on the edge of the woods.    So the blue snow finally makes sense to me.

Once again it makes me wonder about all  I don’t see that goes on in the woods.  Thank you Denise for solving this mystery.