Most people feed birds out of a misguided desire to care for them. Feeding native birds is strongly discouraged as it can lead to health problems or even death for the birds, and issues such as mess and noise for neighbours.
Talk to your neighbour
Learn more about the risks associated with feeding birds so that you can inform your neighbour.
If the birds' presence is not an issue for you, suggest to your neighbour they attract birds to their garden in other ways:
Plant locally native shrubs to encourage nectar-feeding birds.
How to attract birds to your garden (PDF 1.4MB)
Provide a sheltered bird bath or nest box safe from predators and pets, rather than food. How to build a nest box.
You might also suggest that your neighbour become a volunteer wildlife rescuer to care for injured and orphaned birds.
Find your nearest NSW wildlife rescue organisation
If your neighbour won't agree to stop and you are affected by the presence of the birds, your local National Parks & Wildlife Service office may be able to advise on how to tackle this problem.