AGE-RELATED HOARDING STRATEGIES IN THE CRESTED TIT PARUS-CRISTATUS - SHOULD THE COST OF SUBORDINATION BE REASSESSED

1. In a population of crested tits Parus cristatus in northern Belgium , living in group territories outside the breeding season, food was ma inly stored during October and November, a time when territorial flock s are split up in age-specific subflocks. 2. First-year flock members frequently stored in the upper and outermost parts of the trees, where as adults consistently hoarded and foraged in protected sites near the trunk. The outermost, predator-exposed sites were only used by first- year foragers in mixed-age winter flocks with adults, as a result of s ite competition within flocks on cold days. 3. Consequently, the overl ap between foraging sites (protected) and hoarding sites (exposed) of first-year birds was small during autumn, but large during winter. Adu lts, in contrast, consistently showed a large overlap between their ho arding and foraging niche, independently of type of foraging flock. Du e to the segregation of hoarding and foraging sites in autumn, first-y ear birds performed almost six times as many flights within trees as a dults. 4. The overall hoarding frequency (total number of stores per h our) was (i) lower for first-year birds compared to adults, and (ii) i nversely correlated with the proportion of hoarding in exposed sites. We argue that high energetic costs of flying and the high predation ri sk in exposed sites limit the number of stores made by first-year bird s. 5. However, despite their lower hoarding frequency compared to adul ts, first-year birds potentially encounter equal numbers of stores whe n foraging in mixed-age winter flocks, primarily as a result of the hi gh encounter rate in exposed sites. It is therefore argued that the co st of subordination for first-year crested tits might be lower than wa s formerly stated.