FEMALE-FEMALE AGGRESSION AND MONOGAMY IN GREAT TITS PARUS-MAJOR

It has been suggested that female-female aggression may be of importan ce for the maintenance of monogamy in birds. In Europe, Great Tits are monogamous. I tested the aggressiveness of females of this species by presenting a caged conspecific female for 5 min on their territories during the breeding season. A male was presented as a control. Most re sident females were very aggressive towards the female 'intruder', spe nding much of the trial period on the cage, trying to attack. They wer e significantly less aggressive to a caged male. The aggression contin ued if the trial lasted 60 min, both during the stage of incubation an d rearing of nestlings. Females were aggressive even if the cage was p laced 30 m from the nest. The idea is supported that in Great Tits fem ale-female aggression reduces the opportunity for males to attract a s econd female.