Zookeepers at London Zoo conducted their annual animal audit on 26 August. The creatures great and small were weighed to make sure they are all healthy and growing at the right speed.

The reported 17,000 animals living at the zoo must be weighed to make sure they are not getting too fat. But this is not an easy task for the zookeepers, who must think up a variety of ways to get the animals onto the scales.

"We have to use quite ingenious tactics to measure some of the animals," said London Zoo press officer Rebecca Blanchard. "We have to trick some of the animals into being weighed. For example, [for] the Galapagos tortoises, we disguise the scales as a patch of grass underneath the main lawn in their paddock."

Some of the animals are easier to weigh than others, with the penguins being a pick for zookeeper Zuzana Matyasova. "We actually weigh them every single day if we can," she said. It's really easy as [the penguins] like to come up to us, but of course it's very good annually just to set a date and make sure all of our animals are of a good weight and they're growing steadily – especially with young penguin chicks, which we have here this year. We just need to make sure that they're growing as they should be and we can keep an eye on them as well."

Blanchard said the trickiest animals to weigh were the monkeys, "because they just don't stay still for very long. So you've got a fleeting second to get them on that scale, record their weight, before they run off and go and play with something else. So, they've got the attention span of a gnat."

The animals on display on Wednesday included tigers and camels and even some tiny frogs. The information gleaned from the weigh-in is shared with zoos around the world, so that they can compare statistics and adjust feeding plans accordingly. The weigh-in can also help detect whether an animal is pregnant.

While zoo staff are not able to approach some of the more dangerous animals, they are still able to get an their weight. "So things like the big cats here at London Zoo, they're actually weighed inside their den," Blanchard said. "We have scales that are built into their exhibits and into their floors. As they walk [into their enclosure, they'll walk across the scales, so we're able to weigh them regularly - which gives us a regular view on their health."

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