I believe this bird is a wild individual hanging around, having entered the aviary by crawling through the relatively large mesh of this aviary, probably to feed on left-overs from the aviary's inhabitants.
@birdsandbats Not at first sight, no, but be aware that the mesh size is probably somewhat distorted because of the angle the image was taken at and by cropping of the image.
Also, I wouldn't know how these birds could have otherwise gotten in, other than through the mesh.
