Patch Use, Habitat Selection, and Predation Risk in Two Rodent Species in Habiting a Kopje in Tsavo West, Kenya

Abstract

At a kopje in Tsavo West National Park, Kenya, we evaluated several factors influencing foraging of two species of rodents, Xerus rutilus (the unstriped ground squirrel) and Grammomys dolichurus (an African tree rat) in resource patches. We analyzed the foraging ecology of both species in relation to habitat selection (on-kopje or off- kopje/ surrounding savanna), microhabitat (bush and open), food preference (raw peanuts, cooked sunflower seeds, white maize, and yellow com), and plant toxins (oxalates and tannins). By using giving-up densities (GUD: the remaining amount of food in a patch following foraging bouts), we determined that G. dolichurus preferred bush microhabitats and on-kopje habitat. Preference for bush microhabitat probably results from higher perceived predation risk in open areas, the higher risk due to owls. For X rutilus, no significant difference between bush and open or kopje habitat and savanna habitat was found. Either X rutilus perceives both microhabitats and habitats as equivalent in predation risk, or the high foraging efficiency of X rutilus in these resource patches may have prevented accurate results. For diet choice cooked sunflower seeds and raw peanuts were preferred to dried white and yellow corns. We believe that this is the result of sunflowers and peanuts contain higher lipid content and lower handling time than the corns. G. dolichurus showed a tolerance for seeds soaked in tannic acid, whereas X rutilus showed no significant difference between water-treated seeds and tannic-treated seeds. However, oxalates raised the GUDs for both species, suggesting oxalates are a toxin for both species.