Male-male encounters between two species of non American squirrels

Spermophilus tridecemlineatus is a ground squirrel living in North America. At the end of hibernation males start searching for oestrous females. During this scramble competition polygyny, overt conflicts between males may appear. Six dyadic encounters between unfamiliar males were held in the laboratory during the reproductive season. These encounters were compared with similar encounters realized previously on S. mexicanus and S. spilosoma. These three species are joined in the sub-genera Ictidomys. In many respects S. tridecemlineatus appears to be intermediate between S. mexicanus, the less tolerant species, and S. spilosoma, the more tolerant one. One male was dominant over the other male of the dyad only in S. spilosoma and S. tridecemlineatus. Dominance may have evolved in S. tridecemlineatus to decrease the cost of intrasexual competition.