LONDON (AP) — It's tally time at London Zoo: 11 meerkats, 59 penguins, and two endangered Sumatran tigers that keepers hope will bring some cubs in 2013.

Zoo managers on Thursday started an annual cataloguing of its residents, from owls to otters, penguins to pygmy hippos. It's no easy task when there are more than 17,500 creatures to count, and the final tally could take weeks.

The census is required as part of the zoo's license terms, and the data is used for zoo management and international breeding programs for endangered animals.

Most animals in the zoo have microchips in their bodies, making counting a little less daunting. Fish and animals with camouflage properties — like leaf insects — are trickier, and the tiniest ones like ants are counted in colonies, not as individuals.

New additions to the zoo being counted for the first time included baby Ziggy, an endangered white-naped mangabey monkey, and Maxilla, a black and white colobus monkey.

The zoo also welcomed a pair of new Sumatran tigers — male Jae Jae from a zoo in Ohio in the U.S. and female Melati, from Perth, Australia. The tigers were matched by an international breeding program to ensure a genetically-diverse population of animals, and will be meeting visitors in a newly-expanded enclosure in spring.

"They've met but they haven't been introduced to each other yet," said zoological director David Field. "We breed them in the zoo because they are running out of time in the wild."

There are now less than 400 of the big cats, native to Indonesia, according to the World Wildlife Fund.

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  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Bull Frog is held during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • Kepper Amy Callaghan takes a close look at Jill the Red Kneed Spider during the annual stocktake at London Zoo, Thursday, Jan. 3, 2013. More than 17,500 animals including birds, fish, mammals, reptiles and amphibians are counted in the annual stocktake at the zoo. (AP Photo/Kirsty Wigglesworth)

  • A Spectacled Owl nips a clipboard during a photo call for the annual stock take at London Zoo, Thursday, Jan. 3, 2013. More than 17,500 animals including birds, fish, mammals, reptiles and amphibians are counted in the annual stock take at the zoo. (AP Photo/Kirsty Wigglesworth)

  • A meerkat sits on a keepers clipboard during a photo call for the annual stock take at London Zoo, Thursday, Jan. 3, 2013. More than 17,500 animals including birds, fish, mammals, reptiles and amphibians are counted in the annual stock take at the zoo. (AP Photo/Kirsty Wigglesworth)

  • Keeper Jeff Lambert smiles as two leaf insects get close during a photo call for the annual stock take at London Zoo, Thursday, Jan. 3, 2013. More than 17,500 animals including birds, fish, mammals, reptiles and amphibians are counted in the annual stock take at the zoo. (AP Photo/Kirsty Wigglesworth)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: Penguins are fed in their enclosure during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: Otters are fed in their enclosure during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Barn Owl is held during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Diamond Python is held during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • A Spectacled Owl looks at a clipboard during a photo call for the annual stock take at London Zoo, Thursday, Jan. 3, 2013. More than 17,500 animals including birds, fish, mammals, reptiles and amphibians are counted in the annual stock take at the zoo. (AP Photo/Kirsty Wigglesworth)

  • A meerkat stands on keeper Tegan McPhail's clipboard during a photo call for the annual stock take at London Zoo, Thursday, Jan. 3, 2013. More than 17,500 animals including birds, fish, mammals, reptiles and amphibians are counted in the annual stock take at the zoo. (AP Photo/Kirsty Wigglesworth)

  • Keeper Jeff Lambert smiles as two leaf insects get close during a photo call for the annual stock take at London Zoo, Thursday, Jan. 3, 2013. More than 17,500 animals including birds, fish, mammals, reptiles and amphibians are counted in the annual stock take at the zoo. (AP Photo/Kirsty Wigglesworth)

  • A male jungle nymph sits on a female jungle nymph during a photo call for the annual stock take at London Zoo, Thursday, Jan. 3, 2013. More than 17,500 animals including birds, fish, mammals, reptiles and amphibians are counted in the annual stock take at the zoo. (AP Photo/Kirsty Wigglesworth)

  • A muddy Bullfrog is inspected during a photo call for the annual stock take at London Zoo, Thursday, Jan. 3, 2013. More than 17,500 animals including birds, fish, mammals, reptiles and amphibians are counted in the annual stock take at the zoo. (AP Photo/Kirsty Wigglesworth)

  • A muddy Bullfrog is inspected during a photo call for the annual stock take at London Zoo, Thursday, Jan. 3, 2013. More than 17,500 animals including birds, fish, mammals, reptiles and amphibians are counted in the annual stock take at the zoo. (AP Photo/Kirsty Wigglesworth)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Diamond Python is held during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Red Kneed Spider is held during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: Penguins are fed in their enclosure during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: Jungle Nymphs rests on a zookeeper's hand during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Barn Owl is held during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: Otters are fed in their enclosure during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A zookeeper poses with Meerkats during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Bull Frog is held during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Bull Frog is held during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Jungle Nymph rests on a zookeeper's hand during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Diamond Python is held during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A Eurasian Eagle Owl is posed up in front of a clipboard during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: Otters are fed in their enclosure during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • London Zoo Conduct Their Annual Animal Stocktake

    LONDON, ENGLAND - JANUARY 03: A zookeeper poses with Meerkats during London Zoo's annual stocktake of animals on January 3, 2013 in London, England. The zoo's stocktake takes place annually, and gives keepers a chance to check on the numbers of every one of the animals from stick insects and frogs to tigers and camels. (Photo by Dan Kitwood/Getty Images)

  • Counting Creatures at London Zoo

    Keepers at London Zoo have begun the tricky task of the annual stock take, when they count up the many weird and wonderful animals that they care for.