Scent marks signal competitive ability

Malone, N., Armstrong, S.D., Humphries, R.E., Beynon, R.J. & Hurst, J.L. (2005) The signalling of competitive ability by male house mice. In: Chemical Signals in Vertebrates 10 (Ed. R.T. Mason, M.P. LeMaster & D. Muller-Schwarze), pp.77-88. Springer, New York.

At present, there is very little evidence that the chemical synthesis of scents places sufficient energetic limitations on animals to suggest that the material production of scent marks could indicate owner quality. We instead suggest that scent marks are used to signal competitive ability through the spatial and temporal pattern of scent marks deposited by individual males. Furthermore, since these patterns depend on the outcome of competitive interactions between males, scent marks indicate the proven and sustained competitive success of a male, not just his competitive potential. The reliability of these signals comes from the effort required to obtain the opportunity to deposit scent marks in the face of competition from other males. In house mice, the rate of scent marking, the area covered by scent and the streakiness of scent marks all correlate with male competitive ability and are likely to play different roles in the dynamics of competitive signalling. A high rate of territorial scent marking ensures the freshness of the owner’s scent marks, particularly in the vicinity of scent marks from competitors. Thus the most competitive males are able to signal not only dominance over a territory but also up to the minute proof of current ownership and dominance. Widespread coverage of the territory with scent also means that females and rivals are more likely to encounter freshly deposited scent marks from highly competitive males. This dynamic aspect of scent mark deposition patterns may be an important aspect of signalling relative competitive ability in other species that compete for scent marking opportunities. However, further work is required to understand how the behavioural dynamics of scent deposition interact with investment in the material components of scents. Further empirical evidence is also needed to establish the mechanisms underlying the use of scent marks by conspecifics to assess male competitive ability in mice and in other species.