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How do they measure animals for the annual London Zoo weigh-in?

Gorillas beside tape measure Image copyright Reuters

Hundreds of animals at ZSL London Zoo - from the tree frogs to the squirrel monkeys - are being measured as part of the annual weigh-in.

The sizes and weights of the creatures are recorded by zookeepers so they can monitor the creatures' health and well-being.

BBC News looks at the facts and figures behind the event.


Why do they carry out the weigh-in?

Image copyright EPA
Image caption One of the zoo's squirrel monkeys is encouraged on to the scales

There are currently 20,166 animals and 698 different species at the zoo.

While statistics are taken during the year, the zoo say it holds the annual weigh-in to ensure measurements are up-to-date and accurate.

"Weight is a particularly important indicator of health, and we can even detect pregnancies through a growing waist line," ZSL's zoological manager Mark Habben said.

The results are recorded in a database so that zoos around the world can compare information and check their animals are normal and healthy.


What is the heaviest and the lightest animal?

Image copyright Reuters
Image caption Penguins are enticed on to the scales using fish

The heaviest creature in London Zoo is Ellish the giraffe.

The female weighs in at 850kg (133 stone) and stands at 15ft (4.5m) tall.

The lightest creature is a leaf cutter ant which weighs between three and five milligrams (0.0001 oz - 0.0002 oz)


How did some of the animals measure up?

Image copyright EPA
Image caption Kumbuka weighed 191kg at last year's weigh-in
  • Hummingbird - 5g (0.17oz)
  • Jae Jae the male Sumatran tiger - 130kg (4586 oz)
  • Kumbuka the male gorilla - 191kg (6737.33 oz) / 6 ft tall (1.8m)
  • Ganas the Komodo Dragon - 31.8kg (1122 oz) / 1.75m long
Image copyright ZSL London Zoo
Image caption Some of the creatures weighed are more hazardous than others

How are the animals measured?

The keepers have to use various methods to get the creatures on the scales.

Image copyright Getty Images
Image caption Asiatic lions are made to reach upwards to grab food so keepers can measure their heights

The penguins are tricked into walking on to the scales using fish while squirrel monkeys follow a blue ball on a stick.

For larger animals, the scales are disguised as patches of grass in order to record their statistics.

Image copyright Reuters
Image caption Smaller creatures like the fleas flying tree frog are more simple and can be placed on the scales...
Image copyright Reuters
Image caption Although even then, keeping control of them can prove tricky

How does this work help animals in the wild?

Image copyright Reuters
Image caption The weights of even the smallest animals like the spiny turtle are recorded

Much of what is known about the typical weights and measurements of animals has been discovered in zoos.

London Zoo said it meant that people who were studying wild animals could use the zoo's measurements to get a better idea about them.

For example, conservationists in Indonesia are able to tell the rough ages of the tigers they are tracking by measuring the size of their paw prints and comparing them to animals in zoos.

Image copyright ZSL London Zoo
Image caption There are currently 20,166 animals and 698 different species at the zoo

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