LONDON, Jan. 20 (Xinhua) -- Britain's Chester Zoo is home to the highest number of animals in its history, an annual head count of its residents revealed Saturday.

Keepers have completed a month-long task of counting all animals, with the final figure put at 21,314, representing 500 different species. They had to count every mammal, bird, reptile, amphibian, fish and insect.

The number is the highest recorded since the zoo opened in 1931 and is broken down to 1,268 mammals, 1,880 birds, 349 reptiles, 728 amphibians, 7,616 fish and 9,473 insects. The compulsory count is required as part of the zoo's operating license.

Voted on the travel websiteTripAdvisor as the third best zoo in the world, Chester Zoo was last year named as Britain's most popular ticketed tourist attraction outside of London, attracting almost 2 million visitors a year.

Managers at the zoo said the annual census is vital in providing data to plan international endangered species breeding programs.

Liz Ball, from the zoo's records team, said: "The annual animal count at the zoo is always a massive challenge. But with a vast array of new arrivals and well over a thousand recent births and hatchings, this year's count was nothing short of monumental.

"Every animal has its own 'passport', detailing important information such as who it is, where it was born, its gender and its family history. All of these key components are absolutely vital when it comes to carefully pairing up highly endangered animals and co-coordinating worldwide breeding program."

Staff at the zoo has added a whole host of rare new arrivals to their count following a year of important breeding successes.

Among the highlights are two critically endangered Eastern black rhino calves, seven endangered African painted dog pups -- the first of their kind to be born at the zoo -- and world first breeding of highly threatened Bermudian skinks and Catalonian newts.

Mike Jordan, collections director at the zoo, said: "With habitat loss, poaching, hunting, illegal trading, climate change and all manner of other factors affecting wildlife populations around the world, more and more animals are being added to the red list of endangered species.

"The work of Chester Zoo and other good zoos has never been more relevant and important as we fight to ensure a brighter future for so many threatened species," he added.