A zookeeper lures a penguin onto a scale with food during London Zoo's annual weigh-in on Thursday. FRANK AUGSTEIN/AP

LONDON - London Zoo hosted its annual weigh-in for more than 20,000 animals on Thursday, dangling food above lions and placing scales in front of penguins to get them to step onto them.

Used as an opportunity to keep the zoo's records up to date, the measurement and documentation process takes many hours and requires many zookeepers.

Meat is placed above the lions to get them to stand on their hind legs, while penguins are lured onto the scales with food.

The data is then shared with zoos around the world.

"By sharing information with other zoos and conservationists worldwide, we can all use this knowledge to better care for the endangered species we're striving to protect," said Mark Habben, the zoological manager at London Zoo.

The monitoring of the animals is useful for the zoo's commitment to protecting endangered species, while pregnancies can also be spotted. In May, a spiny hill turtle, described by the International Union of Conservation for Nature as endangered, was born at the zoo.

Reuters