As a result of the extreme demands made on
territorial males to reject maturing associates,
their ability to continue territorial defence
declined. Gradually the frequency of this involvement in territorial defence declined as did the
area defended. This left nursing females more
exposed to invasion of their nest sites. Normally
nursing females in the presence of territorial
males exhibit little aggression. However, in
response to invasion of nest sites and bases of
ramps leading to them, the nursing females did
become aggressive, essentially taking over the role
ofthe territorial males.