The huge task is led by zoo registrar Debbie Pearson who is busy tallying up dozens of species including every mammal, bird, reptile, amphibian, fish and invertebrate.
The census, which last year saw more than 2,000 animals counted across more than 140 species, will feature the significant breeding successes of critically-endangered animals including addax calf Tamarisk, born in September.
The register shows how many animals were born or died at the Hampshire visitor attraction, or have been moved in or out within the last 12 months.
Debbie said: ‘Every year we complete the audit in accordance with zoo legislation.
‘It requires each animal collection to keep exact records of every animal species, births, deaths, arrivals into and departures out of the collection.
‘All of this information is then logged into the International Species Information System.
‘It’s a full-time job trying to keep track of all the animals over the course of the year, particularly the larger groups of small animals.
‘It’s a particularly busy year because we are welcoming new arrivals for the Tropical House opening in March.’
Every zoo must undertake the audit and produce a report as part of its licence. Marwell works with a number of endangered species and the annual inventory is designed to ensure the best possible management of worldwide conservation-breeding programmes.
Tiny creatures such as leaf-cutter ants are recorded in colonies, but all others are recorded individually.
Among the animals to be counted are giraffes, slender-tailed meerkats, white rhinos and pygmy hippos as well as the Humboldt penguins.