Comparative Behavior of Male-Female and Female-Female Pairs among Western Gulls Prior to Egg-Laying

The behavior of male-female (M-F) and female-female (F-F) paired Western Gulls (Larus occidentalis) before egg laying was examined on Santa Barbara Island, California to test the hypothesis that one female in a F-F pair may assume a male role. In M-F pairs, no behaviors were performed exclusively by either sex, although males Mounted more often, females Head-tossed more often and males acted more aggressively toward intruders. Within F-F pairs, neither partner consistently showed masculine behavior. In a comparison of behavior toward intruders, both members of F-F pairs resembled the female in M-F pairs, and were generally significantly different from males. We therefore reject the hypothesis that female-female pairing is the result of either the adoption of a "male" behavioral role by one or both partners, or an extreme "female" role by one member.