An Experimental Analysis of Seed Hoarding and Burrowing Behavior in Two Species of Costa Rican Heteromyid Rodents

This study compares the seed hoarding and burrowing behavior of two Costa Rican heteromyid rodents, Liomys salvini, an inhabitant of dry tropical forests, and Heteromys desmarestianus, an inhabitant of wet tropical forests. Because L. salvini lives in a more seasonal and physiologically stressful environment than H. desmarestianus, we initially predicted it would be the more intense seed hoarder and burrower. Results of two sets of five-day seed hoarding experiments indicated that both species cached seeds at a similar rate although H. desmarestianus initially reacted to a 300 gram pile of seeds faster than L. salvini. In both species females hoarded more seeds than males. L. salvini removed more seeds located in an “arboreal” beaker than H. desmarestianus. Both species probably hoard seeds to buffer seasonal fluctuations in food availability. In addition, physiological observations indicate that, unlike L. salvini, individuals of H. desmarestianus cannot tolerate weight losses of 20 percent and hence must hoard seeds to maintain a stable body weight. Results of two-day burrowing experiments in which rodents could choose between placing their nest in an artificial log or nest box or constructing a burrow system indicated that L. salvini is a more intense burrower than H. desma restianus. Eleven of 12 individuals of the former species constructed burrow systems, whereas all 12 individuals of the latter species nested in the log or nest box. Only when the length of the trial was extended to five days and the log and nest box were removed did 50 percent of the H. desmarestianus tested construct a burrow system. Field observations in Costa Rica indicate that live-trapped individuals of L. salvini are more likely to run to a burrow after being released, whereas individuals of H. desmarestianus are more likely to run into or under a log. Perhaps H. desmarestianus places its nests aboveground more often than L. salvini because the physiological disadvantages of burrow systems outweigh their advantages in wet tropical forests.