Sexual and aggressive play fighting of sibling Richardson's ground squirrels

Play fighting in many species of squirrels can involve sexual play and aggr essive play, both of which can lead to wrestling which appears superficiall y similar. Such convergence can make scoring of the relative frequencies of these two types of play difficult and can lead to the mistaken conclusion that they grade into one another. In this study, both staged laboratory enc ounters between sibling pairs and spontaneous encounters between siblings i n free-living litters of Richardson's ground squirrels (Spermophilus richar dsonii) were videotaped. Frame-by-frame analyses using the Eshkol-Wachman M ovement Notation were employed to record the correlated movements of attack and defense by the partners and to reveal the body areas targeted during e ach play bout. Whereas sexual play was organized around access to the rump, aggressive play was organized around the shoulders. Although in most cases the defender's tactics blocked access to the respective target, when conta ct did occur, it involved mounting in sexual play and nosing or biting in a ggressive play. Eighty-six percent of play fights could be unambiguously ca tegorized as either sexual or aggressive play. Of these, the majority (simi lar to 80%) involved sexual play. The sex of the participants did not affec t the frequency of aggressive play, but in sexual play, males initiated mor e attacks than females. Once initiated, each form of play righting remained distinct-if a bout began as sexual play, it would end as sexual play. Furt hermore, a counterattack following sexual play was significantly more likel y to be sexual than aggressive, and vice versa for counterattacks following aggressive play. Therefore, all the evidence suggested that the two forms of play fighting were not intermixed in Richardson's ground squirrels.