Actually they never went away, and they seem to have increased in numbers, as have the honey eaters, ducks, galahs, magpies and the ibis.
The crested pigeons are breeding two months earlier this year, (compared to last year). In the same little tree, just near our dog kennels and the side of the house. They have built another small nest, near their last year's nest.
This is the 2008 nest up above, if you look close near the bird's head you may make out last year's nest.