Cache management by small mammals: Experimental evidence for the significance of acorn-embryo excision

We conducted 2 held experiments to assess relative importance of acorn-embr yo excision in the caching decisions of small mammals, In the Ist, we selec tively provisioned small mammals with metal-tagged acorns of red oak (Querc us rubra) and white oak (Q. alba) at 40 point locations in 8 sites in an oa k 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 s pring and excise embryos of germinating acorns. More excised acorns of whit e oak were found intact in spring than those of red oak, indicating that th e behavior is important for long-term storage of these seeds. In a 2nd expe riment, we presented free-ranging Mexican gray squirrels (Sciurus aureogast er) 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 embr yos removed. Squirrels cached significantly more acorns of white oak specie s, frequently excised embryos of these seeds, and only excised embryos of r ed oaks when they were germinating. These results support our previous hypo thesis that the behavior of embryo excision is geographically widespread an d has important implications for cache-management strategies of some diurna l tree squirrels and their effect on dispersal of oaks.