And while the annual head count helps researchers and maintains licensing requirements, it also poses logistical challenges for zoo workers.
Zookeeper Martin Franklin spoke to the BBC about the difficulties faced by each department:
"I'm lucky in reptiles as we tend to have pretty large animals and it's a walk in the park to count them. We count them every day so we know what we've got but the point is we need to have a snapshot once a year for licensing purposes."
"It's harder for other departments so for example our insects team have a real job on their hands. They might cheat a little bit sometimes and count an entire colony as just one animal but generally speaking, everything is counted."