USE OF FLUORESCENT PIGMENTS IN STUDIES OF SEED CACHING BY RODENTS

We describe a new technique for locating seeds cached by rodents that offers practical and logistical advantages over previous methods. The new technique uses ultraviolet illumination and seeds marked with powd ered fluorescent pigments, which transfer readily between surfaces upo n contact and have been applied successfully for other research on sma ll mammals. We used the technique at a field site in the Great Basin D esert of western Nevada to test and verify the prediction that seed-ca ching, heteromyid rodents would transport a preferred seed type longer distances to make caches in a habitat where this seed is rare relativ e to an adjacent habitat. We also tested two variations of our seed-tr acking technique. The first uses only marked seeds and allows an inves tigator to locate rodent scatterhoards by searching systematically for pigment spots on the ground surface. The second technique requires ro dents to harvest pigmented seeds from a bait station that also is lace d with pigments, so that the animals leave pigmented footprints when t ransporting the seeds. Significantly more seed caches were located, an d the caches were located at significantly longer distances from the s eed source by following footprints with the second technique. Moreover , the footprint trails provided a detailed record of paths traversed b y rodents during seed transport, they revealed locations of rodent bur rows where seeds are stored in larders, and they made it easier to fin d scatterboards.