THE ONTOGENY OF FOOD-STORING AND RETRIEVAL IN MARSH TITS

Marsh tits, Parus palustris, store food and rely on an accurate spatial memory to retrieve their caches. This study considers the ontogeny of storing and the spatial memory involved in retrieving these caches in juvenile hand-raised marsh tits. Preliminary work showed that these birds began storing and retrieving their caches around the time of feeding independence, suggesting that juveniles do not need to learn from adults. However, storing gradually improved over the first few trials, in terms of the appropriateness of items stored, the efficiency of choosing suitable storage sites and the rate of storing seeds. To answer the question of whether the behavioural improvement is a function of age, experience or both, the retrieval performance of two groups of birds were compared. During the first eight trials (24 days) after nutritional independence from the parents, the two groups were exposed to two different kinds of experience: experienced birds were provided with seeds which they could store and retrieve two hours later, whereas the naive birds were exposed only to the storage sites but they could not store. In the following eight trials, both groups were allowed to store and retrieve their caches. If the improvement was merely a consequence of age (maturation) no difference should be found between the two groups on trial 9. In contrast, if improvement was purely a function of experience then the pattern of improvement in the naive group should follow that of the experienced group, but showing an eight-trial time lag. The results suggested a pattern intermediate between these extremes, indicating that either the development of food-storing was a function of both age and experience or that other differences between the two groups, such as differences in motivation to store and/or experience at handling seeds, were important. In contrast, retrieval performance was better than expected by chance on the first trial it occurred and showed little, if any, improvement.