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In rats (Rattus norvegicus), juvenile males engage in more play fighting (a male-typical behavior) than do juvenile females, and this difference is based o perinatal influences of androgens. We show that there are qualitative and quantitative differences between the sexes in the type of defensive responses and their manner of execution. In defensive responses rats try to avoid having their napes contacted by the partner's snout. The sex differences arise from females' greater response distance; that is, females responded to an approach when the partner's snout was further from the nape. This permits females to use different defensive responses and to use them more successfully. This greater response distance is defeminized by the neonatal administration of testosterone propionate. Our findings suggest that play fighting in rats has both male- and female-typical features and that these are, at least in part, influenced perinatally by androgens.

Neonatal testosterone supplementation does not influence adult dominance behavior among male rats, but juvenile play fighting does increase with neonatal hormonal treatment. An analysis of play fighting between pairs of male sibling rats was made in which one sibling in each pair had been injected with testosterone propionate (TP) or oil vehicle and one sibling was untreated. Juvenile TP-treated rats started more attacks, though defense responses remained similar between treated and untreated rats. Adult dominance was not influenced by neonatal testosterone treatment.

The subordinate sibling in a pair of adult male rats is pinned down more often in play attacks because he originates more playful attacks and defends himself in a more juvenile way than his dominant sibling does. A study of 26 male Long Evans hooded rats from five litters analyzed the development of dominance-subordinance relationships. Dominant partners use adult defensive techniques, while subordinates revert to juvenile patterns of turning supine when attacked at the nape.

Studies of intraspecific fighting in two species of voles show that prairie vole resident males attacked the head instead of the rear if the defender turned to face the attacker, but montane vole resident males continued to attack the defender's rear. Videorecorded tapes of defensive and offensive behavior of both vole species were analyzed in depth. The study also revealed that defensive prairie voles retreated after each ineffective defense. Montane voles, however, faced their attackers tenaciously.

Experiments were conducted to study the use of supine behavior as a defensive ploy in male house mice Mus Domesticus. Results indicated that this maneuver is used by mice to prevent attacking opponent from biting them in the region of the lower dorsum. Supine behavior is, therefore, not a submissive tactic but is a dynamic defensive behavior to protect specific areas of the body. The mice do not remain in this position for long, but immediately return to prone position and flee.

A study is made of the fighting/defending tactics and the specific target of attack of the northern grasshopper mice onychomys leucogaster to determine patterns or contextual rules which govern the use of fighting tactics. Results show that the grasshopper mice, which is a very aggressive species, favor the bilateral attack most in fighting/defending an upright defensive posture taken by opponents.

Play fighting is composed of two subcomponent behaviors-attack and defense. If these two components are controlled by the same motivational system, it is expected that they will co-vary. Therefore, it is expected that (1) when species are compared, those that exhibit high levels of playful attack should also exhibit high levels of playful defense; (2) when individuals are compared within a species, those that exhibit high levels of playful attack should also exhibit high levels of playful defense; and (3) developmentally, as play fighting wanes, both playful attack and playful defense should wane simultaneously. A comparison of playful attack and playful defense among six species of muroid rodents reveals that they are not correlated; high rates of defense can occur with low rates of attack, and vice versa. A comparison of individuals from one species (i.e., rats) reveals that those exhibiting the highest levels of attack are not necessarily those exhibiting the highest levels of defense. Finally, a developmental analysis of rats and other species of muroid rodents shows that attack wanes with age whereas defense does not. These data indicate that playful attack and playful defense are motivationally distinct behaviors in these species.