They are evergreen. North of Perth, are you on the coast or inland? Is your climate quite dry or peppered with a degree of humidity? Bougs are native to tropical, quite moist/humid climates, on the basis of the information you've provided about all I can think of is they need moisture. How long have you had them in? Have they been quite 'happy' up till now? More information and perhaps a picture of the plants might help.
Regards.

I'm inland by 40km or so

I don't know how long they have been in as i brought the house with them
they are reaching 12 ft in places so quite a while
the climate is either hot and dry or cold and moist
we have had some cracker cold nights (almost zero) this year but no frosts

they have just had a hell of a lot of rain over the last 2 weeks and were on irrigation before that

to revise my last statement
theres no infection
the leaves appear to be dying from random places in the leave and moving out

close up of a leaf

The winter temps here in my climate just west of Tweed Heads, NSW, rarely drops to that degree, even so my bougainvilleas do drop some, though not all, leaves in winter. Yours might just be dormant, I'd give them a good scrutiny for any residue of insect/grub attack and if you find no trace of an invader you might just have to wait and see if they put on new growth when the weather warms. Down to almost freezing is a bit cool for bougainvilleas.

i may give them a hit with the same stuff i spray the roses (the name passes me)
might feed them some Seasol as well
the weather should turn around now
its never usually that cold but this year has been odd
very dry and very cold

cheers

g'day jumbuck,

dunno if i can help, but you seem to have had a good wet season from all accounts?

they like it very well drained, thrive on neglect.

len

Here is a link that might be useful: lens garden page

Yeah jumbuck, that sounds like a good idea. From the photo, ok, the odd leave is looking a bit ratty but that's to be expected this time of year. Overall the rest look fine and the stems look healthy.

Good luck with it.