They can be very fast. It would be easier to give advice if we knew where you were, and also what species of wattle you had in mind. (There are about a thousand different species) Do you have access to seed?
Trish

I'm in canberra, ACT. We thought one of those pompom blossoms, like the Mudgee. I know a row of the trees close by, If they go to seed then great, if not then I can buy.
VG

Google tells me that mudgee wattle is Acacia spectabilis, which I didn't know. It's called Glory Wattle up here (Toowoomba). Isn't this "common name" business frustrating? how can we ordinary gardeners talk to each other when we can't even agree on the names of common plants?
It also tells me that it grows to 5m in 5 years, apparently in the Canberra area, which also surprises me, as I would have thought two or three metres was the limit. Obviously you live in prime territory, as far as this wattle is concerned! Fast growing can also mean short-lived - as is often the case with the more spectacular flowering wattles. I would guess ten or fifteen years would be its lifespan, but maybe other members could comment on this?
The fastest way to get one is probably to buy one. Make sure it's not very big in the pot, though, as this usually means that the root is curled around to the point where the plant would be "checked" by this.
Growing from seed, and getting it in the ground while still very young would get you a healthier, and perhaps longer-lived tree. The internet says they get to 6 metres. Does your aviary have room for a tree of this size?
Best of luck with it.
Trish

Thanks Trish, That's great.

The aviary is approx. 2.1m but we could prune it to keep it in check.

Can you think of any small-ish shrubs, loose-packed that would help quail hide?

Thanks again for the info, it is really helpful

VG

I'd probably go for one - or a few - of the smaller saltbushes. But I do wonder whether some of the larger grasses would be better? I'm fond of Austrostipa ramosissima, giant bamboo grass, but there are probably a lot of others that aren't quite so big. It gets to be quite a clump, up to shoulder high. Poa species might be good. You'd want something that grows in clumps, rather than something that spreads, I suppose.I've never tried to keep quail, but somehow I imagine them being happy in grass.
Trish

A. spectabilis will be too big for an aviary. Acacia flexifolia is endemic to the Canberra region and will grow to aound 1 and a half metres.