I guess the old saying goes that the illusion of a good image is that its made to look easy. Three things need to happen. The position/pose of the animal, the quality of the light on it (including weather), camera gear and settings are correct for that moment.
Patience is the one key characteristic I have learnt over the many years of shooting Zoos. In my early years I was so impatient. But I had to convince myself/hypnotise! that being patient will have its reward of getting the animal just right. It is in an enclosure so it will always come around. If not this visit, the next or the next. So I make it a point to regularly visit my zoo to keep improving the capture of each of my favourite animals with the intent that one day I will publish my images at least in print for my sons to keep.
The tiger here was trying to hide from something that spooked him. I suspect it was the thunder and lightning that was happening just 5 minutes before the sky opened up and poured like crazy.
I like composing with long super teles for animals as it cuts out all the background and distracting elements and it brings the animals eye closer to the viewer of the image. I used to shoot mostly with 100-400 (both the old and new) but decided that I wanted the smoother rendering and the quality resolving power of primes even on a 7D2 (which is renowned for its noise). So you can imagine, big animal at 400 on a cropped sensor. He is quite a way off.
Indeed the Singapore Zoo, the animals are a way off because it is a large zoo with lots of open spaces and the only thing separating the animals from the people are gullies and a high wall. No glass or fencing (only for leopards and cougars as they can climb!).
The tigers are a supreme challenge for me because its enclosure has too much distractions and the backgrounds are not accommodating. Unlike my Lion images where the backgrounds are a way off and in shadow giving me the chance to shoot with almost black backgrounds. Check them out in this thread.