Squirrel acorn tannins

Vander Wall S (1982) An experimental analysis of cache recovery in Clark s nutcracker. Anim Behav 30 84—946 Squirrels, Acorns, and Tannins... 

Tannin levels vary within an acorn. They are more concentrated in the apical (pointed) portion with the embryo. Accordingly, gray squirrels, and also grackles and jays, selectively consume more often the basal part of an acorn than the distal part (Steele et al. 1993). The embryo will still germinate after being left over by a squirrel. The chemical gradient in the acorn may represent an adaptation that results in a compromise animals consume only the part of the acom that contains the least tannin, but the better protected seedling and parts around it will still survive the predation. 

We will try to test ourselves whether free-ranging (or captive) squirrels discriminate between acorns that have been buried for several weeks and those that have not. In a later laboratory experiment we will analyze tannin levels in the apical and basal poles of acorns, and also compare buried acorns with untreated controls in this regard. We will use the Radial Diffusion Assay for Tannins (Chap. 14). 

It has been suggested that lack of tolerance to tannins may be one reason for the demise of the red squirrel. The grey squirrel is able to consume hazelnuts before they mature, and to survive on acorns. In contrast, the red squirrel has to wait until the hazelnuts are ripe before they become palatable, and it is much less able to survive on a diet of acorns which are the only thing left after the grey squirrels have eaten the immature hazelnuts (Haslam 1998). 

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