the reason why u are not allowed to shoot the pics at the bird shops is very simple: i think last year or 2 years back, there was an investigation on some of the bird shops going on. Basically what happened was that some of these bird shops were involved in the illegal trade of poaching birds from our nature reserves & importing "not ur typical house pet" birds illegally from overseas.
Some passerbys who are very knowlegeable know abt these "not ur typical house pet" and suspect that they could be involved in illegal activities, so they took pictures and informed AVA abt it. Then AVA lauched an ivestigation into them. Subsequently many of the "not ur typical house pet" birds are not displayed anymore in their shops. But to play safe, these shops stopped ppl from photographing their birds.