Thats the old extension of the aviary. Several of the walls of the aviary are capable of sliding open so the birds can have access to the outside. However its been forever since they opened the doors. If I remember correctly they stopped letting the birds out there when they lost a number of the rainbow lorikeets they used to house. The lories developed some kind of brain parasite thanks to raccoon poop. They couldnt keep the coons away an were worried they would lose some of the more valuable birds so it was better to just keep them safe and sound inside. There was a secondary reason they stopped using it too. There is an invasive species of vine... I want to say dog strangling vine... that kept coming back into the exhibit. They fought it for years but after the deaths of the lories they the constant battle against the vines didnt seem as worth it. They have let the exhibit go for years. At times they have housed things like the ring necked pheasants out there just to have something there or just give a home to someone who needed one. Currently its empty.
However there is a plan to open it back up for the birds. The zoo has plans out for bid to do the work so its revamp should happen by sometime next year.
https://www.torontozoo.com/pdfs/rfp/2022/TZC T 41-2022-08 AUSTRALASIA OUTDOOR AVIARY.COMBINED.pdf