Optimization and the Grey Squirrel
October 5, 2005
This morning I set out to add to the cache of walnuts Gary and I collected yesterday prior to the IPM meeting. This turned into an education in the thought patterns of the grey squirrel. I now understand the verb to squirrel. I came upon several of these temporary caches of nuts, tucked in under the edges of rocks, buried in long grass in a shallow depression, or lined neatly along under a disused fence rail. The squirrel’s day seems a constant cost/benefit analysis: effort, security from predators, quality of forage, and competitive effort. For example around the two large trees along the lane, where storage is at a premium yet cover is available, the individuals tended to cache their booty on the ground in a clump of wild raspberry canes, presumably in the hope that other squirrels would not find it. This applies to walnut finds up to about twenty feet from the trunk: no random fall pattern at all. From a single seated position on a rock I was able to collect 100 to 150 nuts per try. Other areas away from the caches were bare of fruit. From 25 to 45 feet from the tree on the sunny side of the trees, however, I observed what I took to be a purely random fall pattern. Obviously the squirrels have decided that the risks of hawk and coyote attack outweigh the potential benefit of the additional nuts. A disquieting thought: the greys may have realized that smaller nuts produce less benefit than larger fruits, and so have concentrated their efforts elsewhere in the forest. I may have collected a burlap bag of their rejects today.
For in the deeper part of the woodlot my efforts went for naught. I visited two dozen of the finest specimens in the stand and found perhaps a dozen prizes, along with coyote scat beneath several of the trees. This produced a mental picture of the coyote lying there, salivating, as the grays cavorted in the branches above, dropping an occasional husk but never leaving the canopy. One eccentric squirrel seems often to husk the nut before transporting it. The abandoned hulls were my only evidence that these trees in fact bore fruit this season. I spotted a few fine green specimens in a decaying maple lying across an abandoned trail. Gritting my teeth at the strangeness of it, I extracted five or six from the hollow log, and a few others which had been hastily concealed. Without a chainsaw I could go no further on this particular raid. My pleasant morning competing with the (invisible) grays has led me to a couple of conclusions about the creation of a walnut nursery on the property: 1. Spacing of plantings must be planned with a view to creating feelings of anxiety among squirrels. A buffer zone around the outside of the plantings might well deter casual feeding if there are less expensive nuts available elsewhere. The zone security could be reinforced with patrols by hunters and/or a border collie who has learned a new, highly specific, herding task. 2. I fervently hope that the walnuts collected were not the squirrels’ rejects. 3. Based upon my observations today, the smaller the nut, the bigger the tree. The main donor trees are both well over 80 years old and have proven themselves extremely hardy and willing nut producers. Yet the nuts are small this year. Younger and I would think inferior specimens in the same stand had large hulls with more of a football shape than the sharply defined and slightly desiccated older trees’ efforts. 4. It’s not hard to understand how the grays have done the plantings, and the pattern of new walnut growth is evidence of Stewart Hamill’s theory that animals need protected routes to promote bio-diversity. Taming the grove without exterminating the squirrels may take some planning, however.