Extramarital and pair copulations in the Cattle Egret

The copulatory behavior of the Cattle Egret (Bubulcus ibis) was observed in a heronry in central Japan. In 38 of 147 extramarital copulation (EC) attempts with seven females, the males seemed to succeed in ejaculation. There were relatively few complete ECs prior to egg laying, because females responded aggressively to approaching males and because the mates of the females stayed in the territories for 78.8% of the time and protected the females. After egg laying, the aggressiveness of females against approaching males deceased and their mates spent more time outside the territories, resulting in an increase in the occurrence of complete ECs. Fighting males that were approaching a female exhibited a dominance hierarchy. The most dominant male stayed in the territory for the longest time and copulated most intensively with his mate and other neighboring females. Extramaritalc opulations are likely to occur in colonial herons, but mate-guarding by the male and aggression by the female mate enhance the probability that copulations will be performed only between members of the pair during the fertilizable period of the female. Thus, the monogamous pair bond is maintained

Masahiro Fujioka, Satoshi Yamagishi, The Auk 98: 134-14