| Abstract: | Three experiments examined the role of timing of breeding in the aggressive behavior and territorial relation in a mixed-species colony of great black-backed and herring gulls. In both species, aggression rates and the percentage of intruders to which they responded increased at hatching. Both species were more aggressive toward herring gull intruders than toward the larger great black-backed gulls. Both species won 40–60% of conspecific encounters with neighbors. In general, great black-backed gulls won their encounters with herring gulls and often succeeded in enlarging their territories into those of neighboring herring gulls and eating the eggs of the herring gulls. However, herring gulls with chicks won 70% of their encounters against incubating black-backed gulls, and they continued to win even when the great black-backed gull's young hatched. These observations indicate that the relative timing of the reproductive cycles of different individuals as well as their size influences the outcome of aggressive interactions and influences reproductive success. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) |
