It was a day of numbers, snacks, and a little bit of animal mischief as two of the UK’s most prominent conservation zoos—Whipsnade Zoo and London Zoo—hosted their annual weigh-ins on August 21, 2025. The event, a logistical feat involving thousands of creatures from the mighty lion to the tiniest frog, offers more than just a quirky spectacle; it’s a cornerstone of modern animal care and global conservation science.
At Whipsnade Zoo, the scale was set for over 11,000 animals, with zookeepers bustling from enclosure to enclosure, clipboard (or tablet) in hand. The pride of ten northern African lions, including seven playful cubs, were among the first to step up for their check-up. For these cubs—born as part of a vital conservation breeding program—the weigh-in isn’t just a formality. According to zookeepers, “the cubs are weighed regularly to monitor their growth and development,” a process that ensures any health issues are caught early and that the young lions are thriving under the watchful eyes of their caretakers. Dad Malik, the pride’s imposing patriarch, tipped the scales at almost 200kg—a stark contrast to his much lighter offspring.
But lions weren’t the only stars of the show. Bactrian camel Sally, a charismatic ambassador for her critically endangered wild relatives, was coaxed onto a giant weighboard with her favorite treats. Sally clocked in at a solid 385kg, more than double the weight of her younger brother Ivor. Born at Whipsnade in May this year, Ivor weighed in at just 106kg—a reminder of how much growing he still has to do. The data gathered from these weigh-ins, according to Whipsnade staff, “will help inform vital research for vets, conservationists, and scientists around the globe who are striving to protect these animals in the wild.”
Elsewhere in the zoo, keepers turned to creative tactics to get their charges on the scales. Pygmy hippo Tapon was lured with a subtle smear of marmite (apparently a hippo delicacy) and settled at 280kg. The northern rockhopper penguin colony, led by zookeeper Natasha Tyrer, hopped onto the scales in turn, with newly born chick Ozzy weighing a dainty 1.84kg. Even Bagot goat Gary got his moment in the spotlight, measured alongside Birch—a giant troll sculpture that, for fun, weighs in at 860kg, the same as a one-and-a-half-year-old southern white rhino calf named Benja.
Meanwhile, over at London Zoo, a similar scene was unfolding. More than 10,000 animals representing 4,000 different species were summoned for their annual check-ups. Among them was Priscilla, a 30-year-old giant Galapagos tortoise, who was gently coaxed onto a board scale with a tempting lettuce snack. Not to be outdone by her Whipsnade counterparts, Priscilla’s slow and steady approach reminded everyone that patience is a virtue—especially when you’re a tortoise.
London Zoo’s animal operations manager Daniel Simmonds emphasized the event’s significance, telling reporters, “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.”
The weigh-in isn’t limited to the big and burly. Tinty Darwin’s frogs, some of the zoo’s smallest residents, measured just two centimeters in length and tipped the scales at under two grams. These tiny amphibians might be easily overlooked, but their health and growth are just as meticulously tracked as that of the largest mammals in the zoo.
Getting animals onto the scales can be a challenge, but zookeepers have developed a toolkit of training methods and enrichment activities to encourage cooperation. Some animals, like the capybaras and Humboldt penguins, have been trained to step onto the scales on cue, often enticed by a favorite snack. Others, such as the ring-tailed lemur troop, bring a sense of lively chaos to the proceedings, but their participation is essential for accurate record-keeping.
All of this data doesn’t just stay within the zoo’s walls. Every measurement is meticulously logged into the Zoological Information Management System (ZIMS), a global database shared with animal carers and conservationists worldwide. According to London Zoo, this system “helps experts to compare important information on thousands of endangered species,” supporting breeding programs, health monitoring, and research efforts far beyond the UK.
Diet and enrichment are central to the animals’ well-being, and the weigh-in provides essential feedback. Daniel Simmonds explained, “Our animals here at London Zoo receive world-class care—and a huge part of this is our meticulous planning of their diets. 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.” Regular weigh-ins help ensure that dietary plans are working and that animals remain healthy and active.
For both zoos, the annual weigh-in is a moment to celebrate the diversity of their animal populations and the dedication of their staff. It’s also a reminder of the critical role zoos play in conservation, education, and scientific research. From the smallest frog to the heaviest troll sculpture, each measurement contributes to a global effort to protect and understand the world’s wildlife.
Beyond the numbers and the spectacle, the weigh-in is about connection—between keepers and animals, between zoos and the wider conservation community, and between the public and the natural world. For many visitors, seeing the care and precision involved in these seemingly routine tasks offers a new appreciation for the work that goes on behind the scenes.
As the data from this year’s weigh-ins is uploaded and analyzed, it will inform not just the day-to-day care of the animals at Whipsnade and London Zoos, but also broader efforts to safeguard endangered species and promote animal welfare worldwide. It’s a process that’s both deeply practical and quietly inspiring, revealing the extraordinary lengths to which zoos go to ensure every creature, great or small, gets the best possible chance at a healthy life.
In the end, while the numbers may be impressive, it’s the stories behind them—the lion cubs growing strong, the tortoise’s slow journey across the scale, the frog’s tiny leap—that truly capture the imagination. And for a single day each year, the humble weigh-in becomes a celebration of life in all its remarkable forms.
