Rare tigers, baby monkeys and waxy tree frogs all joined London Zoo in 2012 but Ricky the penguin is the only rockhopper to be counted in this year's annual stock take.
Some of the world's most endangered species will be counted for the first time, including a pair of Sumatran tigers and Ziggy, a white naped mangabey.
The data will be shared with zoos worldwide to help with breeding programmes so animals like Ricky will be able to mate.
David Field, London Zoo's director, said: "We put all this data together so we know what zoo has what animal. All the work we do here counting the animals is so we can understand what we have and breed together the most genetically important male and females together to breed these incredibly endangered species."
Speaking about Ricky the penguin, whose yellow feathers mark him out from all the others in the country's largest penguin pool, he said: "We have some more penguins coming to join Ricky but he is quite a character. He was hand reared because he was kicked out by his parents."
Adrian Walls, team leader of birds, said: "We hope to be able to find Ricky a partner. We haven't moved him to another zoo what with him being such a diva as he might cause problems."
The zookeepers recorded 17,519 animals in last year's count, with 767 species, but since then the zoo has seen a number of arrivals.
Sumatran tigers Jae Jae and Melati have been brought over to breed their endangered species, replacing elderly Lumpur and Raika who moved to a wildlife retirement home this year after failing to breed.
Mr Field said: "It is so important for us because we are all about tigers in terms of field work, raising funds and also breeding them. The Sumatran tigers are incredibly endangered and there are less than 300 in the wild. Jae Jae and Melati are both ready and in their prime for producing the tiger cubs."
The zoo has also seen the addition of baby black and white colobus monkeys, cotton top tamarins and one rare mangabey, which may bring the total number of mammals up from last year's 500.