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In Pictures: How do you measure a lion? The London zoo weigh-in

Every year, keepers at ZSL London Zoo have to measure hundreds of animals to make sure they are healthy and growing well. How do they do it?
First to the lions. The keepers pop meat up a tree and stick a ruler next to the tree. As the lions reach for their snack, keepers are able to measure how big the lions are.
Lion from London zooReuters
A normal kitchen weighing scale is used for this flying frog. These weigh-ins are important because the information gets shared with zoos across the world. The measurements are used to help zookeepers compare important information about thousands of endangered animals.
Flying Frog,AFP
This Humboldt penguin stands on a set of scales, as every animal is weighed and measured.
Humboldt PenguinPA
Zookeepers use scales, tape measures and rulers to do their mammoth task. This male gorilla named Kumbuka stands next to a measuring board during the annual weigh-in at London Zoo.
A male GorillaEPA
There are more than 20,000 animals and 698 different species at the zoo! These squirrel monkeys are lured onto the scales using food.
A Squirrel MonkeyPA