The Effects of Number and Duration of Visits on Estimates of Seed Removal Rates by Mojave Desert Rodents

Behavioral ecologists are sometimes forced to use indirect approaches to understand foraging decisions of secretive animals, such as rodents. Many foraging experiments have measured rates of seed removal by rodents in artificial trays to estimate giving-up densities (GUDs), but few studies have investigated the diversity of species visiting the trays, the number of individual visitors, and amount of time they spend in the tray. Foraging activity of Merriam’s kangaroo rat (Dipodomys merriami) was documented at seed trays in the Mojave Desert in the Spring of 2012. We used Reconyx PC800 IR-flash wildlife cameras to quantify how rates of seed removal were affected by amount of seed provided, number of foragers, and duration of foraging bouts. Preliminary trials indicated that D. merriami was able to harvest >90% of millet seeds from seed trays over the course of a night, regardless of the amount of seed provided (2 – 16 g). GUDs were similar across all seed amounts provided (0.04 – 0.20 g). Both the number of visits and total time spent in trays increased with increasing seed densities. Foraging visits tended to be shortest at the lowest seed densities, but rodents returned to apparently depleted trays throughout the night. Future foraging trials conducted with dye-marked D. merriami will permit us to determine whether single individuals monopolize trays or if multiple individuals are responsible for our estimates of GUDs. This information on individual activity will provide a more complete picture of foraging behavior at seed trays.