Non-Fibre Values: Red Skies, White Hares, and Blue Pee
- Long May They Wave By Frederick W. Schueler, Bishops Mills Natural History Centre
February 11, 2004, 15h40. I’m standing on 37 centimetres of snow in a narrow glade in a cedar (Thuja occidentalis
) bush on shallow-soil limestone, 400 metres south of Bishops Mills, Grenville County. Lepus americanus
(snowshoe hare) have left an open tracery of tracks and a scattering of pellets on the four-day-old snow surface, and Odocoileus virginianus
(whitetail deer) have slotted trackways through the snow, some of them over-written with Canis
(dog or coyote) tracks.
Deer are increasing explosively in Grenville County, so it’s no surprise that this is the first winter we’ve seen tracks here in the deep snow season. It looks like hare abundance has declined since last year, since if they were abundant, as they have been since 1997, a snow surface like this old enough to be speckled with cedar debris of all kinds - would be solidly and deeply trampled by hares.
We understand why deer are increasing, with recent open winters and various human activities providing them with food sources and refuges from hunting. And curiously enough, from the last digit in the year, I expect the hares to be decreasing, though we don’t have much of an explanation. Hare populations have peaked in the early years of each decade since we’ve lived in Bishops Mills, and now they’re heading down again.
This is the famous ten-year cycle of boreal wildlife, at the southern edge of the area where it is synchronous. The snowshoe hare is the species in which this cycle is best documented, having been traced back to the 1790s in the fur records of the Hudson Bay Company, and to the 1750s in the browsing scars on white spruce (Picea glauca)
in the Yukon. In the Boreal forest the densities of hares may crash in a year from 4,000 per square kilometre to less than one per square kilometre, and then slowly increase to peak densities over the next 6-13 years.
It’s astonishing enough that hare populations should cycle with this regularity. But it’s more astonishing that these cycles should be synchronous within one to two years all across Canada and Alaska, and even more astonishing that they should be “highly positively correlated (P<.0001) with sunspot maxima 4 yr. Previously." 1
It seems that the cycles result from the hares’ interactions with food supply and predators, synchronized across the continent by weather differences that result from the sunspot cycle.
Since we’ve been in Bishops Mills, there have been sunspot maxima in 1979, 1989, and 2000, each time with solar flares that produced an aurora borealis so intense that the sky turned red, and then (in the last two decades), three years later, blue spots on the snow, and the next year, a decline in rabbit populations. Both hares and cottontails, Sylvilagus floridanus
, seem to decline at the same time.
In the winter of 1992, we had pruned some apple (Pyrus malus)
branches and left them on the snow, and rabbits nibbled on the bark of the fallen branches. These were likely cottontails, since the hares don’t usually come from the cedar bush into the village. There was nothing surprising about this, but what was astonishing were spots of bright sky-blue urine in the snow, like windshield-washer antifreeze. Then, after passing through another solar cycle, on 3 January 2002, the snow all was all trampled down by rabbits, and the surface dotted with droppings and two blue, two intermediate, and two brown urine spots. The colour of the bluest of the urine spots was between turquoise green and sky blue.2
In the intervening decade we’d figured out, by trial feeding of goats and domestic rabbits, that this blue urine was caused by a diet of Rhamnus cathartica, the common, European, or cathartic buckthorn, an invasive alien shrub of oldfields and forest edges. 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 199899, 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. Rabbits and deer don’t much favour buckthorn as browse, so these blue spots in the snow can be taken as a sign that they are stressed for food, that their populations are likely to crash, and even that the sky was glowingly red on a night two to three years ago.
Sinclair, A. R. E., Gosline, J. M., Holdsworth, G., Krebs, C. J., Boutin, S., Smith, N. M., Boonstra, Rudy, Dale, M., 1993. Can the solar cycle and climate synchronize the snowshoe hare cycle in Canada? Evidence from tree rings and ice cores. American Naturalist, Vol. 141, No. 2. , pp. 173-198, p 189. <http://hdl.handle.net/1807/443>
2 Members of the NatureList (the Eastern Ontario Natural History list-serve) also observed blue urine spots in this and the following winter, and Bob Arnebeck has posted a picture of one at <http://www.geocities.com/bobarnebeck/bluepee21.jpg>. You can subscribe to the Nature List by sending "subscribe eobm-nat" in the body of a message to <firstname.lastname@example.org>.
About the author - Fred can be reached at the Bishops Mills Natural History Centre, RR#2 Bishops Mills, Ontario, K0G 1T0 or by e-mail <email@example.com>. Visit the Web site <http://pinicola.ca>.
This article appeared in the Winter/Spring 2004 (Volume 34) edition of the S&W Report the newsletter of the Ontario Woodlot Association.