Competitor assessment by scent matching: an experimental test

Summary

If males assess potential opponents by comparing their odour with that of scent marks in the vicinity (the so called ‘scent matching’ hypothesis) they should be more reluctant to fight when these odours are the same. Under these circumstances the potential opponent is thus identified as a resource holder (a male monopolising a territory or group of females) that would escalate encounters to defend its resources. We tested this prediction by comparing the fighting behaviour of male house mice, Mus domesticus, when on a scent-marked substrate that matched the odour of an opponent with their behaviour on a substrate that did not match. As predicted, the delay before the first fight was longer and the rate of subsequent fighting lower when the scents matched. This result is consistent with the interpretation that resource holders scent mark to provide opponents with a means of competitor assessment and that they thus reduce the costs of resource defence.