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Differences in cache placement and pilferage by desert rodents (Family: Heteromyidae)
AuthorSwartz, Maryke Justine
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Desert rodents in the family Heteromyidae cache seeds throughout their home ranges either concentrated in one location (larder hoard) or in multiple, small seed piles (scatter hoards). In order to maintain seed resources and minimize cache pilferage (removal by other rodents), heteromyid species may use different behavioral strategies. I examined caching and pilfering behaviors of heteromyid rodents in the field and laboratory. I first conducted a field experiment to determine which microhabitats species use for caching and pilfering for three coexisting heteromyid rodent species: Merriam's kangaroo rat (Dipodomys merriami), the pale kangaroo mouse (Microdipodops pallidus), and the little pocket mouse (Perognathus longimembris). I tracked cache placement by rodents in outdoor enclosures and measured pilferage of artificial caches of radio-labeled Indian ricegrass (Achnatherum hymenoides) seeds. M. pallidus and P. longimembris preferred to cache seeds under shrubs, whereas D. merriami placed caches predominately in open microhabitat. However, D. merriami showed a significant preference for pilfering caches under shrubs, whereas P. longimembris did not show a significant preference for pilfering caches in either open or under-shrub microhabitats. I suggest that rodents may be selecting their scatter hoarding microhabitats to recover a higher proportion of food and lower the probability of caches being detected and pilfered. For each species, there are trade-offs between costs (e.g. predation risk, pilferage risk) and benefits (e.g. predator-avoidance, pilferage-avoidance) of cache placement and cache removal in each microhabitat. I also conducted a laboratory test and demonstrated that sandbathing behavior by D. merriami increases cache pilferage. During sandbathing, kangaroo rats deposit sebum from a specialized sebaceous dorsal gland and oils from other glands in the skin when they extend their bodies, slide forward on their sides, and rub their ventral regions along the sand. Most males removed more seeds from areas where either they or a conspecific had sandbathed compared to the control area. Moreover, kangaroo rats placed new caches in areas where no sandbathing occurred. However, sandbathing did not affect space use between familiar D. merriami individuals; kangaroo rats spent similar amounts of time in control areas and those with self and conspecific sandbathing loci. I suggest that the olfactory cues left by a sandbathing rodent signal a pilferer that another rodent was there, stimulating a cache search, and thus increase cache pilferage. D. merriami can avoid cache pilferage by sandbathing away from scatter hoard locations. In order to maintain seed resources and minimize cache pilferage by heterospecifics and conspecifics, heteromyid species can employ various behavioral strategies including cache placement in separate microhabitats and cache placement at a distance from sandbathing loci.