Cache recovery vs. pilfering when scatter hoarding seeds: Could predator-prey interactions influence the seed-dispersal process

Background/Question/Methods   Scatter-hoarding mammals are thought to rely on spatial memory to relocate food caches. Yet, we know little about how long these granivores (primarily rodents) recall specific cache locations and whether individual hoarders have an advantage at recovering their own caches. Indeed, a few recent studies suggest that high rates of pilfering are common and that individual hoarders may not have a retriever's advantage. Here we tested this hypothesis in a high-density (>10 animals/ha) population of Eastern gray squirrels (Sciurus carolinesis) by presenting individually marked animals (> 30) with tagged acorns, mapping cache sites, and following the fate of seed caches. PIT tags allowed us to monitor individual seeds without disturbing cache sites.

Results/Conclusions   Cached acorns only remained in the cache site for 12-119 hrs. (0.5-5d). However, when we live-trapped and removed some animals from the site immediately after they stored seeds (thus simulating predation), their seed caches remained intact for significantly longer periods (16-27d). Although some pilfering occurred, cache duration corresponded roughly to the time at which squirrels were returned to the study area. These results indicate that these rodents may have a retriever's advantage, but also show that predation by seed predators could influence the seed dispersal process in some systems.