Keepers at Bristol Zoo say this year's annual census will be made more difficult because of the large number of births in the past 12 months.
The zoo has more than 450 species from tiny insects to gorillas and seals.
A spokesman said many small birds had to be logged as flocks as it was almost impossible to count them individually.
Data from the head count will be submitted to the British and Irish Association of Zoos and Aquariums and shared with other zoos worldwide.
The past year has seen the birth of four meerkat pups, 12 prairie dog pups, three endangered Malagasy giant jumping rats, seven penguin chicks, four flamingo chicks, dozens of seahorses, an okapi calf, a tapir baby and a ring-tailed lemur.
It also received six endangered Egyptian tortoises, which were rescued by customs officials, and was given six Annam leaf turtles from Chester Zoo.
Senior curator John Partridge said the count was needed because it acts as an audit to check that its computer records are accurate.
"Our collection records are far more than a simple count - we know precise information on individual animals and groups, which we share with colleagues around the world to help manage our animals," he added.