The willie wagtail feeds on a variety of insects and their larvae (2) (3) (4) (6), as well as occasionally taking spiders, small fish, worms, lizards and grass seeds (3). An active feeder, it can often be seen darting about as it hunts for prey on the ground. This species also takes insects in the air, often after an acrobatic chase (2) (3) (4) (6), and sometimes follows large animals or even mowers and tractors to catch the insects they disturb (2) (3) (6) (8). The willie wagtail is quite a tame and fearless bird, and often forages close to humans (2) (3) (4) (6), as well as taking insects attracted to street lights or disturbed by passing cars (3).
The characteristic tail-wagging of the willie wagtail is often accompanied by brief flashes of the wings, and both behaviours are thought to be used to flush out insect prey by startling it into flight (3) (5) (7) (8). The willie wagtail is usually seen alone or in pairs, but it may form flocks in winter, often foraging with other bird species (2) (3) (5) (6).
The breeding season of the willie wagtail varies with location, usually occurring between August and January or February in Australia (2) (3) (6), or in any month if conditions are favourable (3) (6). Three or even four broods of chicks can sometimes be raised in a single season (2) (3) (6). The willie wagtail is monogamous (3), and breeding pairs can be aggressive in defending their territory, even chasing away larger animals (3) (6), including humans (3).
Both the male and female willie wagtail help to build the nest, which consists of a neat, rounded cup of fine dry grasses, bark shreds and other plant material, sometimes with animal hair or feathers. The nest is coated in cobwebs and is lined with hair, grass or other fibres (2) (3) (6). Most Rhipidura species build nests that have a wineglass shape, with a hanging ‘tail’ of material below. The willie wagtail is unusual in building a tailless, cup-shaped nest, which may allow it to use a wider variety of nest sites (8), including the horizontal forks of branches, or artificial structures such as fence posts or rafters (3). The nest of this species may be reused over successive years (2) (3) (6).
The willie wagtail usually lays a clutch of three to four eggs, which are white to cream, buff or greyish, and are spotted and blotched with grey or brown. The eggs are incubated by both sexes, and typically hatch after about 14 days (2) (3) (6). The young willie wagtails leave the nest at 11 to 17 days old (3), after which they remain with the adults until the eggs from the next clutch start to hatch (2) (6).
The nests of the willie wagtail are often parasitised by various cuckoo species, and its eggs and chicks can also be lost to predators such as birds, rats and cats (3). However, individuals that survive can potentially live for up to 15 years (6).