Remarkable shot given the light levels in there. I have tried a handful of times without much success to shoot the free flying birds in Tropical Realm. It hadn't occurred to me that the light levels will change much but I will bear your tip in mind and have another go when the sun is shining outside.
Either that or invest in a full frame sensor that can perform like that at ISO 3200!... I may have to stick to Plan A
The light can vary a lot - it's actually like an exaggerated version of what is happening outside - and on a really bright day it is possible to get some action shots. Early in the morning is good before the place fills up, or late in the evening on a clear day as when the sun gets lower it shines in through the windows on the westerly end.
I'm also trying some "stealth" feeder shots using a fast prime, tripod and remote release, but other people seem to want to visit the zoo too... and they're a right nuisance.