 Within a colony , a male bird will occupy an ' activity space ' , which will overlap with the activity spaces of other males . Males with overlapping activity spaces form associations called ' coteries ' , usually consisting of 10 to 25 birds . <unk> are the most stable unit within the colony . The birds also form temporary flocks when engaged in the same activity . These flocks , called ' coalitions ' , usually comprise five to eight birds , although coalitions of up to 40 birds can occur when mobbing a potential predator . <unk> of the coalition changes frequently as individuals leave the group as it passes beyond the boundary of their activity space , or the activity ends or changes , as when the breeding season begins . Females use activity spaces that overlap with those of male birds , but not other females , so that females will join coalitions with males in their area , but only rarely will there be more than one female in the coalition . The exclusivity of female activity spaces leads to young females being driven out of the colony in which they were born , and also makes it difficult for them to gain a place in a new colony . A study of banded nestlings that survived in one colony until the next breeding season , found that they were all male birds , suggesting that all female nestlings had died or left the colony . Emigration of males does not seem to occur until the population density of the colony reaches a critical level . 
