One approach that is starting to reveal interesting variation in social interactions assesses how familiarity of individuals affects their behavior toward one another. This was studied by Prior, Smith, Dooling, and Ball (2020) with a model songbird species, zebra finches (Taeniopygia guttata). This work is important in that it reveals how fundamental simple familiarity-repeated social experience with another individual-is to communication and interaction in social species. More work is now needed, and in a wide range of species exhibiting a wide range of variation in social behavior, to assess the extent to which variation in familiarity is the bridge that links social interactions to social relationships in groups of animals. (PsycInfo Database Record (c) 2020 APA, all rights reserved).