Five Asiatic lions, seven western lowland gorillas, three reticulated giraffes, 53 Darwin’s frogs, and 65 Humboldt penguins—it’s stocktake season at London Zoo. Each January, our zookeepers embark on the monumental task of counting every single animal under our care. While we keep daily records to ensure there are no surprises, the annual census is a formal requirement for our license and an opportunity to update vital data for conservation efforts.
For some zookeepers, the task is straightforward—three giraffes are easy to count. But others face a more creative challenge, especially when dealing with lively primates. Ingenious tactics are often needed to encourage entire troops of monkeys to gather in one place for an accurate headcount. In the case of invertebrates, keepers employ a mix of ingenuity and technology. Hive animals, like honeybees and leaf-cutter ants, are counted as a single colony. When this shortcut isn’t possible, they photograph the critters and tally them from still images.
More than just numbers
Beyond satisfying licensing requirements, the stocktake contributes to an international zoo database called Species360, ensuring that records are precise and up to date. This global database plays a crucial role in managing conservation breeding programmes, which are vital to safeguarding endangered species. These programmes act as an “insurance population,” providing a safety net for species whose wild numbers are dwindling.
The breeding programmes, managed by species specialists across Europe and beyond, are akin to a scientific version of a dating app. But unlike dating apps, compatibility is judged not just on preferences or age but also on genetic diversity. By carefully matching animals, zoos ensure the health and sustainability of their populations, providing a vital buffer against extinction.
Wildlife conservation on a global scale
Knowing how many animals are in these programmes is just as important as understanding the numbers of their wild counterparts. This data shapes global conservation strategies, allowing organisations to prioritise efforts such as habitat restoration, wildlife monitoring, and training local conservationists. At the Zoological Society of London (ZSL), the charity behind London Zoo, population tracking is a cornerstone of our work.
Our expertise extends far beyond the zoo’s walls. ZSL monitors over 30,000 wildlife populations worldwide, spanning 5,000 species. This data feeds into the Living Planet Index, which reveals alarming trends. Since 1970, global wildlife populations have declined by an average of 73%, with some regions, like Latin America, seeing a catastrophic 95% drop. For every 20 animals counted in the 1970s, only one remains today.
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Harnessing technology for conservation
To tackle these challenges, ZSL has embraced cutting-edge technology. Last year, we installed a £2 million supercomputer at our scientific institute. This high-tech tool processes data from satellites, digital cameras, and acoustic sensors, enabling us to monitor wildlife on land and in the oceans more effectively. Visitors to London Zoo might be surprised to learn they are just steps away from a technological hub driving global conservation efforts.
A count that counts
The London Zoo stocktake is far more than a photo-op. It underpins the intricate web of international cooperation required to protect endangered species. Whether counting Sumatran tigers or analysing global wildlife trends, every tally contributes to a broader mission: ensuring the survival of our planet’s most vulnerable species.
As zookeepers wrap up the 2025 count, they’re not just adding numbers to a ledger—they’re playing a pivotal role in a global fight to conserve biodiversity. With partners across the globe, London Zoo’s humble stocktake is a reminder of the power of collaboration and the importance of protecting the natural world for generations to come.
