Swooping occurs during the weeks when a pair has eggs or young in the nest, and is performed almost entirely by males. Surveys consistently indicate that only a minority of breeding males swoop, so most magpies encountered on a footpath are not defenders and never will be. The behaviour ends when the young fledge.
What makes the encounters memorable is selectivity. Australian magpies discriminate individual human faces and can maintain a response to a particular person over long periods, so one resident may be attacked repeatedly on the same route while others pass unbothered. This is consistent with the species' broader social memory in stable groups that hold territories for years.
The song is the other distinguishing feature. Group carolling, with several birds contributing overlapping phrases, functions in territory advertisement, and the vocal repertoire is unusually rich, including quiet subsong and, in some individuals, mimicry of other species and of human-made sounds.