Mandarin Thief

Not a chinese national but a Tui, a native NZ bird which has the most distinctive call, described by someone like a banjo a few weeks ago.
We have about 10 mandarin trees and one in particular has most of its fruit eaten or half eaten. It is not just the Tuis, other birds get in on the act but I think they start off the process by opening the fruit and the others join in later.
The Tui makes a noise when when it flies, someone told me it is the only bird which does so, a bit like the throbbing of a helicopter as it flies past, and the white blob is a ruff which seems semi detached from its throat.
They are lovely birds and and we don't begrudge them a few mandarins. As long as they only feed off the one tree !