CACHE MANAGEMENT BY SMALL MAMMALS: EXPERIMENTAL EVIDENCE FOR THE SIGNIFICANCE OF ACORN-EMBRYO EXCISION

Abstract

We conducted 2 field experiments to assess relative importance of acorn-embryo excision in the caching decisions of small mammals. In the 1st, we selectively provisioned small mammals with metal-tagged acorns of red oak (Quercus rubra) and white oak (Q. alba) at 40 point locations in 8 sites in an oak forest in northeastern Pennsylvania. We then followed the fate of cached seeds by relocating acorns with metal detectors soon after they were cached and again in spring after seeds began to germinate. At least 1 species of small mammal excised embryos of .70% of the cached acorns of white oak and ,4% of those of red oak. Animals also were observed to revisit caches in spring and excise embryos of germinating acorns. More excised acorns of white oak were found intact in spring than those of red oak, indicating that the behavior is important for long-term storage of these seeds. In a 2nd experiment, we presented free-ranging Mexican gray squirrels (Sciurus aureogaster) with pairs of acorns of 5 native white oak and 5 native red oak species and recorded caching events and whether or not cached seeds had their embryos removed. Squirrels cached significantly more acorns of white oak species, frequently excised embryos of these seeds, and only excised embryos of red oaks when they were germinating. These results support our previous hypothesis that the behavior of embryo excision is geographically widespread and has important implications for cache-management strategies of some diurnal tree squirrels and their effect on dispersal of oaks.