Maybe one day they will put something new in there. It doesnt have to be birds. It could be converted to something else and if some minor construction is needed to achieve that goal it wouldnt be as troublesome seeing as nothing lives there now.
Regarding the outdoor area next to the Tree Kangas:
This area has been used. For instance in 2013 the weeds, foliage, and underbrush were all cleared out and Kookaburras were out there (alternating the two females - you could hear them calling, one inside, one outside). The zoo was holding four rooks temporarily and that's where they were. The Shovellers were out there, briefly I think.
The area is difficult because of West Nile virus, Avian Flu, raccoon feces, and Dog Strangling Vine (see below).
Most of this I knew but confirmed some and learned more from the senior keeper there yesterday.
From Ontario Invasive Species Awareness Program web site:
Impacts of Dog-Strangling Vine
Dog-strangling vine forms dense stands that overwhelm and crowd out native plants and young trees, preventing forest regeneration.
Colonies form mats of interwoven vines that are difficult to walk through and interfere with forest management and recreational activities.
Leaves and roots may be toxic to livestock. Deer and other browsing animals also avoid dog-strangling vine, which can increase grazing pressure on more palatable native plants.
The vine threatens the monarch butterfly, a species at risk in Ontario. The butterflies lay their eggs on the plant, but the larvae are unable to complete their life cycle and do not survive.