A zookeeper weighs Humboldt penguins during the London Zoo annual weigh-in event on August 24, 2016. Home to more than 700 different species, ZSL London Zoo staff regularly record the heights and weights of all the creatures at the zoo as a key way of monitoring the residents’ overall well-being. This important information is shared with zoos around the world to help zoologists compare details on thousands of endangered species. (JUSTIN TALLIS/AFP/Getty Images)

Oh my, look how they've grown.Penguins, squirrel monkeys and tigers are just some of the animals that were weighed and measured at the annual weigh-in event at the ZSL London Zoo in London, England, last week.

Home to 17,000 animals and 712 different species, the ZSL London Zoo is the world's oldest scientific zoo. Staffers regularly record heights and weights of all the animals through the yearbut the annual weigh-in is an opportunity for keepers at ZSL London Zoo to make sure the information they've recorded is up-to-date and accurate, as well as to monitor the animals' health and well-being.

Each measurement is then added to the Zoological Information Management System (ZIMS), a database shared with zoos all over the world, helping zookeepers to compare important information on thousands of endangered species.

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"We have to know the vital statistics of every animal at the Zoo—however big or small," Mark Habben,ZSL’s zoological manager, . "This information helps us to monitor their health and their diets and by sharing the information with other zoos and conservationists worldwide, we can use this knowledge to better care for all our animals."

Aside from keeping track of animals’ general well-being, keepers can also use regular weight checks and waist measurements to identify pregnant animals, many of which are endangered species that are part of the Zoo’s international conservation breeding programs.

According to Habben, the heaviest animal at the zoo is a giraffe weighing in at 1,898 lbs, and the lightest is a leaf cutter ant, which is so miniscule, "it wouldn't even reach the scale in the grams."

But weighing all the animals is no easy task, and zoo staffers used special tricks to get them to hop on scales.In the squirrel monkey enclosure, to persuade the jumping little animals to stay on the scales long enough for a reading, according to Reuters, while the penguins got on scales in exchange for a fish treat and the tigers jumped for meat on a pole.

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