What are the most important factors in choosing a mate? What determines whether mates are compatible? Many of the same questions surround mate choice in both humans and monogamous birds. For birds with enduring pairbonds, finding a mate that is a "good match" can be as important as finding a mate with "good genes." Behavioral compatibility between mates increases reproductive success, and likely depends on the "fit" between mates' personalities (i.e., underlying characteristics that describe and account for enduring patterns of behavior). Studies show that (1) in a number of species, animals' personality traits can be characterized with high inter-rater agreement and reliability and are stable across time and situation, and (2) these traits influence ecologically-critical behaviors (e.g., foraging, dispersal) in both captive and wild animals. However, the relationship between personality, mate choice, and compatibility remains largely unexplored. These are also crucial conservation issues: many threatened species (e.g., parrots, cranes) are also those for which pair compatibility is most important. Accordingly, the objectives of this series of three studies are: (1) to characterize personality in cockatiels, (2) to determine whether mates' personality traits are correlated, and (3) how this correlation relates to pair behavioral compatibility.

Based on these studies, several conclusions may be drawn. First, cockatiels' behavioral characteristics can be measured using psychometric methods. Ratings based on the behavioral-rating instrument used in this project clearly reflect behavior observed during the ratings phase and show significant inter-rater agreement and adequate reliability. Additionally, these ratings predict birds' behavior in novel situations. Second, cockatiels use behavior as a mate choice criterion. Females that paired successfully had fewer aggressive interactions with their eventual mates than did unpaired females with their male social partners. Females also pair assortatively based on personality traits: very agreeable and very disagreeable females pair with males that are significantly more agreeable than the mates chosen by females with intermediate agreeableness scores. Assortative pairing may limit intrapair conflict. Finally, personality "match" between mates affects pair behavioral compatibility and reproductive success: successful pairs show a significantly better match between mates' agreeableness scores than unsuccessful pairs, as well as better coordination of incubation.