Food caching and differential cache pilferage: a field study of coexistence of sympatric kangaroo rats and pocket mice

Ecologists studying sympatric heteromyid rodents have sought evidence for s pecies differences in primary foraging abilities and preferences and/or beh avioural responses to predation risk in order to explain coexistence. The p resent field study was conducted to test the hypothesis that another factor may be involved, namely differences in caching patterns, which may result in differences in vulnerability to pilferage. We examined differences betwe en kangaroo rats (Dipodomys merriami) and pocket mice (Chaetodipus spp.) in foraging, caching and pilferage behaviour. Specifically, we examined inter actions at food patches, differential food caching patterns, and differenti al vulnerability to cache pilferage. Observations conducted at artificial s eed patches showed that kangaroo rats dominated access to the patches by ar riving and foraging first and by chasing pocket mice away. Individually pro visioned pocket mice stored most seeds in underground burrows (larder hoard ing), whereas kangaroo rats predominantly cached seeds in small, spatially dispersed caches in shallow pits in the surface of the sand (scatter hoardi ng). Pocket mice pilfered from each other as well as from the kangaroo rats , but the kangaroo rats rarely pilfered, and the only instance was from ano ther kangaroo rat. Kangaroo rats and pocket mice were both vulnerable to ca che pilferage. The results suggest that coexistence of kangaroo rats and po cket mice may be facilitated by a trade-off between primary harvest ability and the ability to exploit a resource that has been processed by another s pecies, namely pilferage ability.