They were ugly as sin, but they were capable of being restored - aviary partitions being removed, rewired, and softened up with vegetation. Certainly the Zoo has nothing as tall and as useful today.
They stretched along the Eastern boundary, encompassing the Macaw Aviary, but going further North and South. They were knocked down in 1985, with the intention of creating a new pathway to a brand new Aquarium that would have stood where the Parrot House was. All came to naught when Westminster refused permission for the latter's demolition.
The site stood empty and grassed over until the Macaw Aviary was built in 1994, although as I say it takes up nowhere near the same amount of space.
I wonder how many of these aviaries there actually were?, there seamed to be quite a lot from what I recall, also the dead rats placed in them for the birds food.