Seasonality of Food Use and Caching in New Zealand Robins (Petroica Australis)
Foraging behaviour in birds is strongly determined by temporal factors such as season and time of day. Most birds show a limited number of food use methods such as consuming, feeding to conspecifics, or discarding. A relatively small number of birds also cache food for later use. The expression of caching in birds has been attributed to numerous factors. However, noting the environmental instability experienced by most caching species, researchers tend to cite survival of future food scarcity as the predominant advantage. Recording the food use behaviour of wild birds is typically difficult and time consuming, and many studies of north-temperate food-caching birds are limited by long caching distances, protracted caching durations, and a lack of year-round data. Additionally, food-caching in Australasian passerines has received limited quantification. The naïveté of the New Zealand robin (Petroica australis) makes it ideal for behavioural observations in the wild. Robins express a wide range of food use behaviours within close proximity of observers, and cached food is retrieved within a few days. Food use can be observed year-round in a temperate environment that is relatively stable. Thus, food use decisions in robins can be assessed in a wider context. In this study, behavioural data were collected from robins inhabiting the Karori Wildlife Sanctuary in Wellington. Robin behaviour was quantified by presenting monogamous, paired birds an ephemeral food resource and observing their responses. Seasonal variation in food use differed with sex and season. Birds mediated their food use in response to the presence of conspecifics. Males dominated food use year-round. During the breeding season, males cached little, mostly feeding familial conspecifics. However, non-breeding males selfishly cached food. Conversely, female caching propensity was mediated by courtship feeding during the breeding season, and the threat of male pilferage outside of it. Birds did not appear to anticipate future food scarcity. Instead, food was cached in the season in which retrieval would be least necessary. In robins, food is opportunistically cached, mainly as a competitive response to excess food.