Hens with bilateral ablations in the hyperstriatal complex were compared with birds with bilateral ablations in the posterior telencephalon and sham-operated controls with regard to their behaviour in their home pens, exploratory behavior and their responses to (1) a simulated aerial predator, (2) a startling stimulus and (3) an auditory stimulus. Ablations involving the ventral hyperstriatum made the birds less reactive to frightening stimuli while ablations in the posterior telencephalon resulted in the bird "freezing" in the experimental situations.