Seasonal changes in and effects of familiarity on agonistic behaviors of rat-like hamsters (Cricetulus triton)

The seasonal changes in agonistic behaviors and effects of familiarity on agonistic behaviors in wild-caught adult rat-like hamsters (Cricetulus triton) were observed in dyadic encounters in a neutral arena. The aggression of opposite- and same-sex encounters became higher or remained the same during the non-breeding season. This indicates that the hamsters were solitary during both seasons. Familiarity increased the aggression in male-male encounters and decreased the aggression in female-female encounters during both seasons. Familiarity also increased the aggression in female-male encounters during the non-breeding season and had no effect on the aggression in female-male encounters during the breeding season. These results may be related to the hamster's social structure. The more agonistic acts both male and female hamsters had, the more frequently they marked using flank glands during both seasons. This implies that flank gland marking can be used to advertise status and can be assessed by opponents to reduce the agonistic costs.