Common Myna
Acridotheres tristis
Common Mynas are indeed very common in Sydney, being one of the most numerous birds in towns and cities in the area. They were first introduced from Asia (hence the other common name of Indian Myna) in the 1860s and further introductions continued until the 1950s as they were thought to be useful in eating pest insects (which they weren't). They in turn have become agricultural pests as they eat grains and fruit from farms. Another major problem is that they compete with native species for nesting sites, throwing out existing nests, eggs and chicks. They are a member of the starling family and, when domesticated, can be excellent mimics. They are 23-25 cm in length.
1: Taronga Zoo, NSW, 01/07/2010.
2: Royal Botanic Gardens, Sydney, NSW, 31/10/2009.