A comparison of the reaction of sticklebacks in different reproductive conditions towards conspecifics and predators

Experiments are described which assess ‘boldness’ towards a pike and ‘aggressiveness’ towards conspecifics in sticklebacks in non-reproductive condition, with a newly-built nest and with a recently hatched brood of young. The level of both of these aspects of behaviour increased across the three conditions. The possibility that this covariance indicates shared internal causal factors for the response to predator and conspecific is discussed.