On a bright August morning, the familiar hum of Regent’s Park was punctuated by an unusual flurry of activity: zookeepers with clipboards, scales of every size, and a parade of animals ranging from towering giraffes to minuscule frogs. It was August 19, 2025, and London Zoo’s much-anticipated Annual Weigh In had officially begun, kicking off a week-long operation to record the vital statistics of more than 10,000 animals. According to BBC News, this massive undertaking is no small feat, requiring meticulous planning, patience—and, as it turns out, plenty of snacks.
The weigh-in event is a highlight on the zoo’s calendar, drawing attention not just for its adorable photo opportunities, but for its crucial role in animal care and conservation. Every mammal, bird, reptile, fish, and invertebrate across the zoo is weighed and measured, from the stately ring-tailed lemur troop to the world’s largest rodents—capybaras Gizmo and Kiwi. The process is as much about science as it is about spectacle. As the zoo explained in footage shared on the day, keeping tabs on each animal’s weight and measurements is essential for monitoring their health, tracking development, and even identifying pregnancies.
Getting such a diverse cast of characters onto the scales, however, is no easy task. Zookeepers employ a range of training techniques, sometimes placing scales in doorways or cleverly disguising them in habitats so animals can be weighed without even realizing it. For others, a bit of positive reinforcement does the trick. Take Priscilla, a 30-year-old giant Galapagos tortoise, who was lured onto a board scale with a tempting lettuce snack. Meanwhile, the Humboldt penguins—never ones to be left out—lined up enthusiastically for their turn, jostling in front of zookeeper Jessica Ray. As BBC News reported, snacks are often the secret weapon in encouraging even the most reluctant residents to step up.
But why go to all this trouble? According to the zoo’s Animal Operations Manager, Daniel Simmonds, the Annual Weigh In is far more than a quirky tradition. “The London Zoo Annual Weigh In is not just about numbers on a scale; regular weigh-ins help zookeepers track the health of our animals—including the capybaras, tortoises, and penguins—and genuinely help us manage the care of these animals, who play a vital role in our global conservation efforts,” Simmonds told reporters. The data collected is meticulously logged into the Zoological Information Management System (ZIMS), a global database shared with animal carers and conservationists around the world. This allows zoos everywhere to compare vital information on thousands of endangered species, helping to inform best practices for animal care and breeding programs.
London Zoo’s animal collection is nothing short of extraordinary. Beyond the headline-grabbing capybaras and tortoises, the institution cares for creatures as tiny as Darwin’s frogs—measuring just two centimeters in length and weighing under two grams. Each animal, regardless of size, receives the same attention to detail. Regular checks ensure that any notable weight changes are promptly investigated, which can be a crucial early warning sign of health issues. “Being weighed isn’t about dieting—it’s a crucial tool for monitoring each animal’s wellbeing,” Simmonds emphasized.
The scale of the operation is truly impressive. Over the course of a week, keepers will work their way through the zoo’s entire population, which numbers more than 10,000 animals. The effort doesn’t end once the last animal steps off the scale. All the information gathered is shared with conservation organizations worldwide, contributing to a broader understanding of animal health and population trends. As noted by BBC News, the results from this year’s weigh-in will be distributed to conservationists and zoos across the globe, strengthening collaborative efforts to protect endangered species.
Of course, the weigh-in isn’t just for the animals’ benefit—it’s also a hit with the public. The event offers a rare behind-the-scenes look at the care and dedication that goes into running one of the world’s most famous conservation zoos. Visitors (and online audiences) are treated to delightful scenes: a capybara named Gizmo patiently sitting on a scale, ring-tailed lemurs being tempted with treats, and penguins waddling up for their turn. The footage, which quickly made the rounds on social media, captured the hearts of animal lovers everywhere.
For the keepers, the event is a chance to showcase the science behind their work. Many animals are trained to perch on a scale, while others are weighed as part of their daily routines. Zookeepers also use the opportunity to check that the information recorded for each animal is up-to-date and accurate. “Our animals here at London Zoo receive world-class care—and a huge part of this is our meticulous planning of their diets,” Simmonds explained. “Our zoo-tritionist ensures every animal is getting the nutrients they need, while our keepers devise ways to feed the animals that spark all of their natural instincts—keeping them fit and challenged.”
In addition to the scientific and conservation goals, the Annual Weigh In has an educational mission. This summer, London Zoo is inviting children to join the Zoo Crew—an initiative that lets young visitors step into the roles of Zookeepers, Field Conservationists, and Scientists through hands-on challenges and costume dress-up activities, all included for free with their entry ticket. It’s a clever way to inspire the next generation of wildlife champions, making the science of animal care accessible and fun.
The Annual Weigh In is a reminder of the complexity and importance of modern zoo work. Gone are the days when zoos were simply collections of exotic animals for public display. Today, institutions like London Zoo are at the forefront of conservation science, education, and animal welfare. Their work extends far beyond the boundaries of Regent’s Park, impacting species survival efforts and research projects around the globe.
As the week unfolds and the last animals are coaxed onto the scales, the data collected will join a vast international network of knowledge—helping to shape the future of wildlife conservation. For the keepers, it’s a labor of love; for the animals, perhaps just another day with a few extra snacks. For the rest of us, it’s a captivating glimpse into the dedication required to protect the planet’s most remarkable creatures.
