Magpies are well known for attacks on humans during the breeding season, which peaks from August to October, however nesting can take place anytime from July to December.
Magpies only swoop when they have chicks in their nests. This is a natural behaviour, typically performed by the male magpie to ward off perceived intruders.
Only a small proportion of magpies ever attack people. Magpies will usually only defend area of around 100 m radius; concentrating their activity on the zone around the nest tree. Magpies swoop to scare the intruder away from the nest, not to cause injury.