Why are the birds not coming back to Tenterfield?

For the passed few years I have noticed a steady influx in the return of certain species to Tenterfield but at the same time these same species are not staying here any more. Some species have opted to only raise a family in Tenterfield and then move on again, whereas others have taken up residency here albeit are tiny numbers. The large majority of birds that left Tenterfield became migratory species, only rarely coming back to Tenterfield and only for food.

Tenterfield has somewhat remained the same over the years and although only a small handful of trees have been removed for various reasons (including via floods) it does not make sense to me that the birds would not become residents again even with the return of the rain. Something is missing in this scenerio that I am overlooking as to why the birds are not moving back to Tenterfield.

The majority of the species are attracted to the Tenterfield Creek whether to nest near the water or to use it somehow. Its strange but I've never actually seen any birds drink out of the Tenterfield Creek. They seem to prefer to drink from puddles away from the creek itself.

Birds follow food sources, whether it be natural or offerings by humans. Birds prefer natural food over artificial sources in this area. They only eat human offerings because of the lack of their own food in the area. But this is strange because no great loss of flora has been happening in the area since 2001. Plant and tree seeds are still being eaten by birds, nectar is still available in the area - otherwise the rosellas (Eastern) would've left by now. Insects are in abundance right now; and aquatic life is flourishing as the White-faced Heron was seen a few days ago with a male, so she may decide to breed again - twice in 12 months.
Even birds of prey have been on the increase, hence being sighted or their scats found - so there is not much to really stress birds out in the way of a lack of food right now. But I have noticed the King Parrots have not come back yet - even though they may be breeding right now - they should be back by now.

Maybe trying to solve the mystery of why King Parrots left in the first place (some years back) might help to solve the mystery of why many other bird species left. Okay, let's find out what King Parrots eat...
Firstly they eat seeds, and lots of them. In the areas I've observed them eat the seeds of Pine Trees, Oak trees, Wattle trees, and grass seeds. Doing a bit more research on the net, King Parrots also eat fruit, berries, Eucalyptus nuts and buds, wild tobacco, honey, and insects.

If this is what King Parrots depend upon to survive it might explain why the majority of this species left town, as there is not much of anything available in between early Autumn and early Spring. All the gum and pine trees go to seed in Summer; Wattles go to seed from October to December; Oaks in Summer; there are no native fruit or berries in the area - all blackberry bushes have been poisoned by the Council; no wild tobacco in the area; which leaves honey and insects. There are Banksias in the area but I'm not sure when they go to flower. Native bees are in such small numbers that any honey is simply not enough for one King Parrot let alone a lot of them. Insects have been numerous - not prolific - since the rains returned in October 2012. I doubt it has anything to do with this because over a period of time these food sources (except the Blackberries) have remained constant and in the same quantity of plants.

In the last few years the temperature has fluxuated dramatically. We have had quite a few warm to hot winter seasons but that seems to be going back to normal now. I really think it has something to do with the weather than their actual food supply that not only made these birds leave but to also not come back.