I should have checked that - they can't be painted storks because the black and white pattern on the wings would be quite distinctive so they must be milky storks.
SZ doesn't really keep many birds and most are in the Fragile Forest exhibit. I have seen Eclectus Parrot, Sun Conure Parrot, Red Lory, Spotted Whistling Duck, Common Crowned Pigeon, Nicobar Pigeon, Pinon's Imperial Pigeon, Pied Imperial Pigeon, Green Imperial Pigeon and Pink-necked Green Pigeon there. Other than that all that I can think of are a Rhinocerous Hornbill in the Proboscis Monkey exhibit near the entrance (there are 2 PM exhibits), a couple of Saddle-billed Storks in the Great Rift Valley of Ethiopia, Ostrich and Grey Crowned Crane in the Wild Africa exhibit and Emu and Cassowary in the Australian Outback exhibit.