Hyperdispersed cache distributions reduce pilferage: a field study

Many animals hoard food when it is plentiful for periods when it is scarce. The time between storage and retrieval can be a matter of hours to months. To increase the probability that hoards will still be available when needed, hoarding should happen in such a way that it reduces cache loss. Scatter hoarders can do this by manipulating the density and dispersal of caches to minimize the foraging efficiency of pilferers. Previous work has shown that there is an optimal density that reduces cache loss. We investigated whether cache distribution patterns can be manipulated to reduce cache loss. We distributed seeds in a uniform, random or clustered manner in the field and tested their survival. More hyperdispersed distributions reduced seed loss, indicating that these distributions may be useful to hoarding animals. The most clustered distributions of seeds became more hyperdispersed as time progressed, decreasing the risk of discovery for the remaining caches. This suggests that hoarders could adopt the alternative strategy of hoarding a larger number of items to begin with, allowing initial cache loss to produce a more hyperdispersed distribution gradually as the clustered sections are removed. Further work needs to investigate whether it is evolutionarily adaptive to invest in hoarding more items or to invest in a hyperdispersing strategy. Our results also show that seeds disappeared at a lower rate in the winter, suggesting there is some degree of safety for hoarded food when it is needed most. (c) 2007 The Association for the Study ofAnimal Behaviour. Published by Elsevier Ltd. All rights reserved.