Behavioural traits can vary between individuals from the same population. These differences can involve
consistent variation in the level of a particular behaviour (personality) or differences in the way individuals
adjust their behaviour to environmental gradients (plasticity). In prey species, feeding rates and
vigilance vary with environmental, social and individual factors and the feeding rate/vigilance relationship
reflects the trade-off between food acquisition and safety. While feeding rates and vigilance
have been shown to vary between individuals in relation to group size and predation risk, how they
relate to other factors has not yet been investigated, nor has between-individual variation in this tradeoff.
We studied between-individual variation in vigilance, feeding rates and their trade-off in female
eastern grey kangaroos, Macropus giganteus, to see whether females showed consistent behavioural
differences and different plasticity in relation to ecological (food patch richness), social (group sizes) and
physiological (reproductive states) conditions. We addressed two contrasting hypotheses: an ‘ecological’
hypothesis under which individuals facing the same conditions should behave similarly, and a ‘behavioural’
hypothesis under which they should behave differently because of their own personality or
plasticity. Female kangaroos tended to adjust their behaviours similarly in relation to ecological and
social conditions, supporting the ecological hypothesis. However, they also showed differences in personality
and plasticity in relation to their reproductive states that could not be explained by energetic
demand alone; this was suggestive of different maternal strategies, thus supporting the behavioural
hypothesis. Altogether these results suggest that consistent differences in animals’ personality and
behavioural plasticity can be promoted by physiological conditions and are not necessarily repeatable
across different ecological contexts.