Dicing with death: predator inspection behaviour in minnow shoals

When shoaling minnows encounter a stalking pike, fish leave the shoal, approach the potential predator and then usually halt briefly before returning to the group. This behaviour, termed predator inspection, has been reported from encounters with both real and model pike. A description of inspection behaviour is given using data from experiments with a model pike made to approach foraging minnows with a standardised stalk. Evidence is presented that inspecting fish assess the risks involved. Individual minnows which have carried out an inspection visit to the predator model exhibit changes in behaviour on return which are contingent upon the state of the model, demonstrating that information is gained. Other fish change their behaviour after an inspector returns to the group, suggesting that information about the threat is transferred among the shoal. Possible costs of predator inspection behaviour may balance these benefits of knowledge, but require further investigation.