Corticosterone responses and personality in birds: Individual variation and the ability to cope with environmental changes due to climate change.

Birds can respond to an internal or external stimulus with activation of the HPA axis and secretion of corticosterone. There is considerable individual variation in corticosterone responses, and individual responses can be very different from the mean response for a group of birds. Corticosterone responses and behavioural responses to environmental stimuli are determined by individual characteristics called personality. It is proposed that birds with low corticosterone responses and proactive personalities are likely to be more successful (have greater fitness) in constant or predictable conditions, whilst birds with reactive personalities and high corticosterone responses will be more successful in changing or unpredictable conditions. The relationship between corticosterone responses and fitness thus depends on the prevailing environmental conditions, so birds with either low or high corticosterone responses can have the greatest fitness and be most successful, but in different situations. It is also proposed that birds with reactive personalities and high corticosterone responses will be better able to cope with environmental changes due to climate change than birds with proactive personalities and relatively low corticosterone responses. Phenotypic plasticity in corticosterone responses can be quantified using a reaction norm approach, and reaction norms can be used to determine the degree of plasticity in corticosterone responses of individual birds, and mean levels of plasticity in responses of species of birds. Individual corticosterone responses and personality, and reaction norms for corticosterone responses, can in future be used to predict the ability of birds to cope with environmental changes due to climate change.