Not mentioned many birds sofar but a species very rare about 20 years ago and now quite common is the Steller's Sea-eagle - they even can be seen in Flight-shows now - see this picture http://www.zoochat.com/457/stellers-sea-eagle-376285/ !
On the other hand, the Great Indian hornbill, a bird which could be found in almost every zoo or even the smallest birdpark about 30 years ago, has almost disappeared !
Stellar's Sea Eagle? I've still only ever seen one at the Woodland Park Zoo. I have seen quite a few Southern Ground Hornbills, but very few Abyssinian Ground Hornbills.