Somebody tell them ground squirrels that potato leaves are poisonous! By Irene Shonle

I have all the greens in my garden covered by floating row covers, but my potatoes are hanging out unprotected.   The deer come by occasionally and eat all the flowers, but recently the Golden Mantled Ground Squirrels or perhaps the chippies have been eating the leaves off the lower branches!

Chipmunks or ground squirrels eating the lower potato leaves.

I don't think they're doing a lot of damage this late in the game -- I'll be harvesting in a few weeks, anyway, but I'm wondering why they can eat them.  Any green parts of potatoes (including green skinned potatoes themselves) contain solanine, which is toxic even in small doses (http://www.nlm.nih.gov/medlineplus/ency/article/002875.htm).  Why are they suffered no ill effects?  (And no, it wouldn't break my heart if they did suffer ill effects).
Perhaps this article sheds some light on the situation: http://www.ncbi.nlm.nih.gov/pubmed/10794631
(It basically says what we know about many plants - that alkaloids vary over time and location).  Maybe the plants are giving up their alkaloid defenses, because they "know" the end is near, and the leaves matter less now in the grand scheme of things.