More than 17,000 animals live at ZSL London Zoo, and yesterday keepers spent the day weighing and measuring many of them.
The regular weigh-ins help keepers to monitor the health of the animals. The information they gather is shared with zoos around the world, to help with breeding and conservation programmes.
Yesterday, all manner of animals from young penguin chicks to giant tortoises took to the scales, some more willingly than others. Penguins were weighed as they lined up for their morning feed, and the tortoises were trained to walk over scales in their paddock.