From Wikipedia they seem to be as bad as humans
During the breeding season, pied currawongs will pair up and become territorial, defending both nesting and feeding areas.
However, they are seen as beneficial in forestry as they consume phasmids, and also in agriculture for eating cocoons of the codling moth.
The pied currawong is an omnivorous and opportunistic feeder, eating fruit and berries as well as preying on many invertebrates, and smaller vertebrates, mostly juvenile birds and bird eggs, although they may take healthy adult birds up to the size of a Crested Pigeon on occasion. They will hunt in
trees, snatching birds and eggs from nests, as well as insects and berries from trees.
They also hunt in the air and on the ground
Insects predominate in the diet during summer months, and fruit during the winter. They will often scavenge, eating scraps and rubbish and can be quite bold when seeking food from people.
Beetles and
ants are the most common types of insects consumed. Pied currawongs have been recorded taking
mice, as well as
chickens and turkeys from farms.
[48] The pied currawong consumes fruit, including a wide variety of figs, such as the Moreton Bay watkinsiana),[49] as well as lillypillies
Other fruit is also sought after, and currawongs have been known to raid orchards, eating apples, pears, strawberries, grapes, stone fruit, citrus, and corn
Pied currawongs have been responsible for the spread of the invasive ornamental Asparagus aethiopicus (often called A. densiflorus) in the Sydney area, the weedy privet species Ligustrum lucidum and L. sinense, and firethorn species Pyracantha angustifolia and P. rogersiana around Armidale.
I dont think you will get rid of them easily. Could you run wires or rope across areas to reduce them flying down?