One-by-one the animals at ZSL London Zoo jumped onto the scales for their annual weigh-in on Thursday (August 24).

In order to check their waist lines are not growing too wide, penguins, monkeys and frogs took to the scales while the lions and gorillas were measured with a good old fashioned ruler.

There are more than 20,000 animals at London Zoo, and the keepers spend hours recording heights and weights throughout the year.

The annual weigh-in gives the keepers the opportunity to make sure the information they have recorded is up to date and accurate, with figures then being shared to the Zoological Information Management System (ZIMS) - a database which allows zoos all over the world to share information on endangered species.

One of the penguins weighed 4.25kg

ZSL’s zoological manager, Mark Habben, explains it is all about monitoring the health and well-being of the animals.

He said: "We have to know the vital statistics of every animal at the zoo – however big or small.

The lions are encouraged to reach up for their breakfast

"It helps us to ensure that every animal we look after is healthy, eating well, and growing at the rate it should – weight is a particularly important indicator of health, and we can even detect pregnancies through a growing waist line!

"By sharing information with other zoos and conservationists worldwide, we can all use this knowledge to better care for the endangered species we’re striving to protect."

Even the baby gorilla of the gang has to be measured

Some animals, rather like a lot of humans, are scale shy and the zoo keepers have to adopt a number of different methods in order to encourage the animals onto the dreaded platform.

The Humboldt penguins are enticed onto the weighing table as they line up for their morning fish and the lions are encouraged to reach up to breakfast hanging from a tree so their full height can be measured.

The Bolivian squirrel monkeys needed some encouragement onto the scales

Coming in at an average penguin weight, Heathcliff was 4.25kg; more than four times as heavy, one of the pygmy goat's weighed 19.7kg.

On the lighter end of the scale, Bolivian squirrel monkey Eubie weighed 1.2kg, with the zoo's spiny hill turtle weighing 53.5g.

The smallest of the lot was the fea's tree frog, weighing just 20g.

Heidi the Asiatic lion stretched up to 6ft tall and 20-year-old Kambuku was measured at 4ft tall.