Cache spacing patterns and reciprocal cache theft in New Zealand robins

Abstract

We quantified cache spacing patterns, cache retrieval rates and rates of cache theft in New Zealand robins, Petroica australis. In a field experiment we presented wild birds with a superabundant supply of mealworms. Trials were conducted on competitively dominant males and subordinate females, both when birds were alone and when they were accompanied by their mate. We hypothesized that (1) dominant males would aggregate caches to facilitate their defence, whereas subordinate females would scatter their caches more widely to avoid their discovery by males, (2) sexual differences in cache spacing would be context dependent, or occur only when birds were in pairs, and (3) patterns in cache spacing would facilitate cache retrieval and reduce cache theft. Females cached food further from food sources than males when they occurred in pairs. However, both sexes cached at similar distances when they were alone. Regardless of social context, females created more cache sites than males, and both sexes created more cache sites when they were together. Cache theft was frequently observed. Female-made caches were retrieved at similar rates by both males and females whereas male-made caches were more likely to be stolen by females than retrieved by the males that made them. Therefore, the results showed no support for the hypothesis that cache spacing patterns reduce cache theft. We suggest that the apparently conflicting relations between cache spacing, recovery and theft are determined by a trade-off between winter survival tactics and mate provisioning.