Personality in animals has been investigated across a variety of different scientific fields including agricultural science, animal behaviour, anthropology, psychology, veterinary medicine, and zoology. Thus, the definition for animal personality may vary according to the context and scope of study. However, there is recent consensus in the literature for a broad definition that describes animal personality as individual differences in behaviour that are consistent across time and ecological context. Here, consistency refers to the repeatability of behavioural differences between individuals and not a trait that presents itself the same way in varying environments. Animal personality traits are measurable and are described in over 100 species. Personality in animals has also been referred to as animal disposition, coping style, and temperament. There are also personality norms through the species, often found between genders. The diversity of animal personality can be compared in cross-species studies, demonstrating its pervasiveness in the evolutionary process of animals. Research on animal personality variation has been burgeoning since the mid 1990s. Recent studies have focused on its proximate causation and the ecological and evolutionary significance of personality in animals. Animal personality vs. human personality The extent of personality phenomena considered when examining animal personality is significantly reduced compared to those studied in humans. Concepts such as personal objects, identity, attitudes and life stories are not considered relevant in animals. Similarly, any approach that requires the subject to explain motives, beliefs or feelings is not applicable to the study of animal behaviour. The study of animal personality is largely based on the observation and investigation of behavioural traits. In an ecological context, traits or ‘characters’ are attributes of an organism that are shared by members of a species. Traits can be shared by all or only a portion of individuals in a population. For example, studies in animal personality often examine traits such as aggressiveness, avoidance of novelty, boldness, exploration and sociality. Background The initial framework used to study animal personality was comparative psychology. The descriptive language used by comparative psychologists in the late nineteenth century often attributed disposition and behavioural tendencies to individual animals in their studies. Many of these reports are the result of researchers anthropomorphizing the animal subjects and did not explicitly examine what is now considered animal personality. However, these studies do represent the some of the first instances of scientists reporting individual differences in animal behaviour. Russian physiologist Ivan Pavlov was one of