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Foraging height (mean+s.e.m.) for blue tits and great tits: (a) in August–September, and (b) in April. Open bars, juveniles; filled bars, older birds. Cross-fostered birds were reared by the other species. Sample sizes are shown above bars. The p-values refer to t-tests between cross-fostered birds and controls. Age of focal bird had no significant effect in these comparisons.
