Agonistic Behaviour Between Pairs of Hamsters of the Same and Opposite Sex in a Neutral Observation Area

The agonistic behaviour of pairs of hamsters when placed for 10-15 minutes in a neutral cage was observed. The first step in an encounter between two animals of the same sex is usually unilateral or mutual investigation. The aggressively dominant animal initiates investigation more frequently than his partner. Dominance is usually established by one animal winning all the interactions in any one test; in many cases this is accomplished by ritual postures during sparring, although overt fights occurred in about half the tests. Body weight was positively correlated with aggressive success. There was no sex difference in any measures of agonistic behaviour. In encounters between animals of opposite sex, the male almost invariably starts sniffing and following the female. If she is in oestrus, she responds by lordosis and active copulation follows; there is almost no agonistic interaction. On the contrary, a sexually unreceptive female often shows aggression towards the male who may respond by evasion or counter-attack. Even when matched for weight, females win most of the encounters. When their sexual advances are rebuffed by the females' offensive behaviour, males frequently engage in cage marking. Maximal agonistic behaviour as well as marking occurs at the mid-point of the cycle between consecutive oestrous periods.