Sexual differences in food re-caching by New Zealand robins Petroica australis

We presented monogamous pairs of New Zealand robins Petroica australis with a Superabundant Supply Of artificial prey and then observed birds re-cache previously hoarded prey. Males and females frequently relocated and redistributed previously hoarded prey. Both sexes also re-cached prey that was originally hoarded by their mare. However, re-caching rates of retrieved and pilfered prey differed between sexes. Female-made caches were re-cached at the same rate by both females and pilfering males, while male-made caches were re-cached more frequently by pilfering females. The re-caching of previously hoarded prey is consistent with the hypothesis that re-caching reduces theft. However, re-caching pilfered prey suggests that it might also play a role in cache theft strategies. Higher rates of re-caching by pilfering females cannot be explained by current hypotheses used to account avian re-caching behaviours. We suggest two new hypotheses, sexual dimorphism in spatial memory and indirect mate provisioning, which may help to explain the evolution of re-caching in New Zealand robins.