Density‐Dependent Survival of Scatterhoarded Nuts: An Experimental Appoach

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Abstract
We tested our earlier prediction that the food content of buried nuts will influence the density at which fox squirrels (Sciurus niger) scatterhoard each species of nut. We buried black walnuts (Juglans nigra), bur oak acorns (Quercus macrocarpa), and chinquapin oak acorns (Q. muehlenbergii) at varying densities in monospecific and mixed—species grids in three different years and three different seasons within a year, and analyzed their survival from predation over time. We also observed free ranging squirrels scatterhoard walnuts and bur oak acorns, which we made available in equal numbers. The survival of buried nuts was dependent on the nut species, nut density, and squirrel density. The lowest meaningful density of buried nuts for squirrels was related to the food content of the nut species. Analysis of nut survival at the same burial sites in successive seasons indicated that squirrels did not use memory to return to specific sites where they had previously found nuts. Rather, they foraged preferentially in certain microhabitats. Squirrels were observed burying black walnuts farther away from a source pile than they buried bur oak acorns. The difference is consistent with the difference in food content between the two species and also with the threshhold density below which naive squirrels have no density—dependent effect on buried nuts. Our data on nut survival suggest that squirrel foraging varies with nut density but not with nut spacing.

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