Exposure and time use in willow tit flocks: the cost of subordination

Time budgets of wintering willow tits, Parus montanus, differed between tree species (spruce and pine) and between different portions of trees. Habitat use appeared to be governed by a trade-off between feeding and being vigilant. Time-economizing favoured flocking, since the improved predator protection in flocks allowed savings in vigilance time to be made; dominant status further gave a net benefit in less time spent being vigilant because dominants had access to protected sites. This suggests that flock size is determined by the stable outcome to the dominant-subordinate conflict rather than by a solution that is optimal to all members. Subordinates are relegated to more exposed parts of the habitat and suffer a cost in spending more time being vigilant. Subordinates still make a net profit in joining flocks, however, and their participation can be viewed as a time-saving behavior.

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