CACHE DISPERSION AFFECTS RETRIEVAL TIME IN HOARDING WILLOW TITS

Six free-roaming flocks of Willow Tits Parus montanus were supplied with radioactivity labelled sunflower seeds in two experimental designs. In the first design all seeds were given at one location in the territory. The tits then retrieved most hoarded seeds in a few days, similar to Marsh Tits P. palustris encountering an ephemeral food source during the winter. In this situation, food is stored at a high rate and retrieved shortly after storing. In the second design the same amount of seeds was provisioned at five different sites in each territory. This design resulted in more widely distributed caches which increased retrieval time by a factor of four. This shows that retrieval time is dependent on the distribution of caches in the territory. Other factors than cache dispersal that may affect retrieval time in tits, such as the energetic value of food are also discussed. Finally, possible mechanisms affecting the evolutionary stability of hoarding in tits, are outlined.