Predictability as a personality trait: consistent differences in intraindividual behavioral variation

Although animal behavior is generally repeatable, most behavioral variation apparently occurs within rather than across individuals. With the exception of very recent interest in individual behavioral plasticity (consistent differences in responsiveness), this within-individual variation has been largely ignored despite its importance in the study of proximate and ultimate questions about behavior. Here, we repeatedly scored the undisturbed activity of 30 adult male mosquitofish across multiple observation bouts spanning 132 days ([Formula: see text] observations per fish). We found that the behavior of some individuals was consistently more predictable in a given context than others. Repeatability for this "intraindividual variation" (IIV; [Formula: see text]) was evident after accounting for individual differences in activity trends across days, and activity responses due to fine-scale temperature variation (i.e., individual plasticity in response to both variables). To our knowledge, this is the first evidence that predictability of behavior is a repeatable characteristic of individual animals. We suggest that IIV represents an important axis of consistent behavioral variation that has previously not been formally considered. Finally, individual differences in predictability may similarly exist for labile morphological and physiological traits but have seemingly not been studied.