Contest behaviour varies in relation to reproductive opportunities and reproductive success in the fallow deer

Abstract

Theory expects contestants to adjust their investment in fighting in line with the perceived value of a resource. Thus, we expect to see an increase in contest duration or aggressive actions if the subjective value of the resource is estimated to be high relative to occasions where the value is estimated to be low. Although this expectation is well established in theory, we know little about how contestants structure their contests over resources in the wild: in particular, how variation in resource availability affects how contestants invest in fights. The objectives of this study were twofold: to examine whether (1) the structure of male–male fights varied with presence and abundance of oestrous females in the population and (2) there was an association between investment in fighting and mating success, during fights between fallow deer, Dama dama. Subordinate but not dominant contestants increased their rate of attacking actions when there were oestrous females in the population. However, there was no association between dominant or subordinate contest actions and variation in the number of oestrous females on any single day. Regarding mating success, dominant males that increased their attack rate during fights were more likely to achieve a mating than those that did not, although this investment in attacks was not associated with the number of matings obtained. Conversely, mating success was associated with a reduction in the number of parallel walks for subordinate contestants. Therefore, subordinate males achieved more matings when ritualized display behaviour was reduced or omitted from the contest. These results suggest that a desperado effect may be present, and that contestants use an estimate of resource value rather than opponent quality when investing in contests.