engage with mutual agreement, but if any noticeable asymmetries are seen, such as a broken or lost weapon, this may alter the behaviour of an individual to engage in a fight. Likelihood and severity of antler damage were looked at in fallow deer, to test whether antler damage was associated with contest tactics and duration, and if an association existed with the tendency for individuals to engage in fighting. Individuals with undamaged antlers were more likely to attack, using high-risk tactics that included jumping, clashing, or backward-pushing behaviour, this was exhibited by both contestants; dominant males were more likely to have damaged antlers. Dominance ranks exist within fallow deer populations, which can be linked to aggression level and body size; when competing for a male, however, how ranks are obtained is not studied extensively. Endurance rivalry Male fallow deer are highly competitive during the rutting season; successful mating depends mainly on body size and dominance rank. Many factors can determine the seasonal reproductive success of an individual male fallow deer; these factors include body size, which can affect reproduction and survival. The amount of time spent in a lek can be an important factor in determining male reproductive success; energy can play an important role for the duration of competitive leks. Among ungulates, European fallow deer exhibit one of the most outstanding examples of sexual dimorphism, as males are much larger than females. For sexual selection to lead to the evolution of sexual dimorphism, where males are bigger than females, advantages must be present: (1) Advantages during combat, (2) Endurance rivalry advantage, (3) Female preference for larger males, and (4) Advantages during sperm competition. Sexual selection has chosen bigger males over an evolutionary time scale and conferred advantages during competition of mates by a variety of mechanisms, which are intrasexual competition, access to females, and resource accessibility, which affects attractiveness to females. Body size is important during male-male agonistic interactions and endurance rivalry, while females tend to have a preference for larger males. Dominance rank is a good indicator of body size and body mass, but age was not an important factor. In a study done by McElligott et al. (2001), it was found that mating success was related to body size, pre-rut and rut rank. Similarly, in another study, researchers found that age, weight, and display effort were all significant factors in determining mating success; in both studies, mating