Individual animals from the same population, sex, age and reproductive status often respond differently and consistently to predators. One important dimension of this behavioural variation is the shy-bold continuum. Innate differences in boldness might explain why individuals differ in their antipredator behaviour. In a laboratory experiment, we examined the sources of individual variation in antipredator behaviour of adult male lizards Lacerta monticola. We simulated in the laboratory repeated predatory attacks of low or high risk and analysed activity levels and refuge use in both situations. Multivariate analyses suggested the existence of two consistent and independent shy-bold continua. The first described a gradient from bold lizards that spent shorter times in the refuge after predatory approaches to shy lizards with longer emergence times, whereas the other described a gradient from bold lizards with a low propensity to hide when the predator was close but risk was low to shy lizards that hid more often. We analysed whether morphological characteristics, body condition and health (estimated from their T cell immunocompetence) of individuals might account for the differences observed. Bold individuals had smaller absolute body size, but relatively larger heads, better body condition and better health. Bold individuals with a low propensity to hide when risk was low had larger absolute body sizes, whereas relative head size, and body condition and health were not important. We suggest that the position of an individual in the shy-bold continua might reflect its optimal antipredator behaviour, which would be a function of its health, general quality and ability to evade predators.
Bibliographical noteFunding Information:
We thank three anonymous referees for very helpful suggestions, and ‘El Ventorrillo’ MNCN Field Station for use of their facilities. Financial support was provided by the MCYT project BOS 2002-00547, by an El Ventorrillo C.S.I.C.-C.M. grant to L.A., and a CEE BIODIBERIA grant to D.H.