My mom always said that the local woodchuck would come out of his (her?) burrow on Feb. 2. If the light was sufficient to see his shadow (below Zone V, I'm sure), he (she?) was frightened and ran back inside for six more weeks. As a former research scientist, I can assure all that the beast always sees his shadow and spring comes at the usual time (excepting global warming - global warming???).
Truly dr bob. :-)