My recommended quick route around London Zoo
Enter zoo, turn right and enter aquarium, exit aquarium, go to Mappins.
Then enter Komodo dragon house, exit and view Galapagos giant tortoises.
Enter reptile house through side door or go to front entrance to ensure you complete the full loop of the building inside.
Leave reptile house, enter Gorilla Kingdom.
Exit Gorilla Kingdom, go through African bird safari aviary then see Casson pavillion/Zoo World.
Go through animal adventure starting at farmyard end. Exit animal adventure and view big cats.
Then BUGS building , anteaters also here but probably in indoor shelter to right of toilets opposite BUGS. Go through the monkey walkthrough at this point, the exit brings you out by the Blackburn Pavillion entrance.
Blackburn Pavillion, enter then exit and walk along back of BUGS building towards penguins. You will pass parrot aviaries, flamingos and pelicans.
After penguins go back towards the square with the cafe and shop and carrousel. Go down tunnel between cafe and shop.
Turn left on other side of tunnel. See otters, lemurs, meerkats, bat house and Clore. Continue to Cotton Terraces. Go along front of terraces (left hand side) for paddocks with tapir, giraffe, zebra and okapi. Follow path round and loop back via warthogs, hunting dogs and giraffe house interior.
Cross bridge to North Bank and aviaries. This is where the zoe's imperial pigeon is. Exit via North Bank turnstile exit if you are leaving via Camden Town.
If you are quick and don't linger at each exhibit you can see pretty much everything I think.