The combined effects of seed perishability and seed size on hoarding decisions by Pere David's rock squirrels

The food perishability hypothesis reasons that the perishability of nondormant acorns through rapid germination is the primary determinant of hoarding decisions (e.g., embryo removal in nondormant acorns in particular) by scatter-hoarding squirrels. However, we do not know whether seed size and its interactions with seed germination schedule affect squirrel's hoarding decisions. By presenting pairs of acorns with contrasting germination/dormancy conditions and seed size, we investigated the relative importance of each target trait in determining the hoarding decisions of free-ranging P,re David's rock squirrel (Sciurotamias davidianus) in Central China. Consistent with the food perishability hypothesis, the squirrels were highly sensitive to subtle differences of acorn germination status either within nondormant acorns or between nondormant and dormant acorns. Though there were no significant differences in seed hoarding and dispersal distance, the embryo-removal probability of nondormant acorns (especially those germinated) was much higher than that of dormant acorns prior to hoarding. Our results also support the seed size hypothesis. Large acorns were often hoarded more and moved farther than small acorns, and large nondormant acorns also had a higher probability of having their embryos removed. Moreover, the interactions between seed size and seed germination schedule had a large effect on whether a given acorn was hoarded or hoarded with its embryo removed. Our study indicates that the combined effects from seed germination schedule and seed size have the potential to determine hoarding decisions of scatter-hoarding squirrels.