Willie Wagtails are members of the Flycatcher family and are related to Crows, Ravens, Drongos and Birds of Paradise. They're a common sight throughout mainland Australia although not found in Tasmania.
These swiftly moving birds are insect eaters and are often seen following sheep and cattle, or standing on the animal's back before launching themselves into wild aerial manoeuvres to catch whatever insects are disturbed, as the stock move around. (Their nests are tidy and cup-shaped and woven from grass, spider web, sheep/alpaca wool and even dog or cat hair.)
Their call is said to resemble "Sweet, pretty creature" and it does too! I'd love to tag this particular chap, because I'm sure his territory covers the entire length and breadth of my street.