Despite a rapid increase in animal personality research, critical gaps remain. We have little knowledge of the long-term (as opposed to short-term) consistency of personality and the relationships between personality and behavioural flexibility in wild, free-living animals. This study investigates personality (i.e., consistent inter-individual differences in behaviour) and contextual plasticity (i.e., plasticity in behaviour between contexts) of these traits in the Nazca booby (
Sula granti), a long-lived, free-living seabird. We tested birds for personality in the field, during incubation, using a human intruder test, two novel object tests, and a social stimulus test (mirror), and determined repeatability of behavioural traits both within-season (short-term) and between several years (long-term). We found high short- and long-term repeatability of aggressive and anxiety-related behaviours when confronted with a nest intruder and novel objects, but lower repeatability during social stimulation. Contextual plasticity was highly repeatable across years for aggressive behaviours, and low for anxiety-related behaviours. Plasticity did not correlate across behaviours into a meta-personality trait. Contextual plasticity in behavioural traits was highly correlated with the expression of those traits, suggesting that individuals are able to both react strongly and modify their behaviour depending on context, perhaps due to consistent differences in individual quality. Model selection exercises using structural equation models evaluated the relationships between personality factors, indicating a behavioural syndrome in which anxiety- or agitation-related behaviours covary strongly and positively, and both covary weakly and negatively with aggression.