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 mainly stored during October and November, a time when territorial flocks are split up in age-specific subflocks. 2. First-year flock members frequently stored in the upper and outermost parts of the trees, whereas 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 site competition within flocks on cold days. 3. Consequently, the overlap between foraging sites (protected) and hoarding sites (exposed) of first-year birds was small during autumn, but large during winter. Adults, in contrast, consistently showed a large overlap between their hoarding and foraging niche, independently of type of foraging flock. Due to the segregation of hoarding and foraging sites in autumn, first-year birds performed almost six times as many flights within trees as adults. 4. The overall hoarding frequency (total number of stores per hour) was (i) lower for first-year birds compared to adults, and (ii) inversely correlated with the proportion of hoarding in exposed sites. We argue that high energetic costs of flying and the high predation risk in exposed sites limit the number of stores made by first-year birds. 5. However, despite their lower hoarding frequency compared to adults, first-year birds potentially encounter equal numbers of stores when foraging in mixed-age winter flocks, primarily as a result of the high encounter rate in exposed sites. It is therefore argued that the cost of subordination for first-year crested tits might be lower than was formerly stated.