The annual weigh-in is a big event for ZSL London Zoo, and 2023 marked the 100th year of the tradition. Each year, zookeepers pull out their best tricks to lure their unsuspecting residents onto the scales, something IFLScience got to witness in person as we were invited down to see what goes on.
Armed with tape measures, giant rulers, and the all-important scales, the zookeepers weigh every mammal, bird, reptile, fish, and invertebrate within their walls. In total it amounts to some 14,000 animals, meaning the whole operation takes several days.
Snacks are gold dust throughout the proceedings, with each animal being motivated by a different treat to coax them onto the scales. For squirrel monkeys, it was nuts and popcorn; for the penguins, it was sprats (a few of which ended up in the mouths of the city's wild herons); and for tigers? Well, apparently they’re fond of curry powder.
We caught up with some of the keepers to find out more about why the annual weigh-in is so important, and how the data they collect can contribute towards the conservation of wild animals.
As well as updating their records, the annual weigh-in gives ZSL London Zoo an opportunity to contribute to the Zoological Information Management System (ZIMS), a database shared with zoos all over the world. It helps zookeepers to compare important information on thousands of endangered animals, benefiting the health of animals enrolled in species-saving breeding programs, and giving us vital stats that can help us measure the health of wild populations.
“We record the vital statistics of every animal at the Zoo – from the tallest giraffe to the tiniest tadpole," said Head of Zoological Operations Angela Ryan, in a statement.
“Having this data helps to ensure that every animal we care for is healthy, eating well, and growing at the rate they should - a key indicator of health and wellbeing. For example, a growing waistline can help us to detect and monitor pregnancies, which is vitally important as many of the species we care for are threatened in the wild and part of international conservation breeding programmes - London Zoo coordinates the global programme for Sumatran tigers, for example.”
And it’s hella entertaining to watch, too.