More than 19,000 animals are stepping on the scales for their annual weigh-in at ZSL London Zoo as it warned of the “catastrophic” impact of the coronavirus crisis.

Penguins, squirrel monkeys and camels were among the creatures to have their height and weight recorded on Thursday, which allows zookeepers to monitor their health and wellbeing.

Forced to close for an unprecedented three months due to the pandemic, the Regent’s Park zoo says a loss of income from ticket sales has put a “huge financial pressure” on its operation.

Sir David Attenborough and comedians including Jonathan Ross and Catherine Tate have fronted videos aiming to raise funds for the Zoological Society of London, which runs London and Whipsnade zoos.

More than £1 million per month is needed to care for the animals and, while zoos were allowed to reopen on June 15, social distancing means visitor numbers have been limited.

Dominic Jermey, ZSL director general, said: “The impact of coronavirus on ZSL cannot be understated.

“Lockdown saw us closed for longer than any time in our history with fixed costs of more than £1 million a month just on food and care for our animals, let alone our conservation and science and almost no income.

“Being back open is really positive. But with social distancing limiting visitor numbers, we are nowhere near able to make up the shortfall.

“This has been catastrophic for us and we are seeking funding from a range of places.”

Each year, zookeepers armed with clipboards and calculators tally up every mammal, bird, reptile, fish and invertebrate at the zoo – home to more than 600 different species.

Four-month-old otter pups Bubble and Squeak took to the scales for the first time, while pregnant okapi Oni tipped the scales at 288kg, a few kilos heavier than her pre-pregnancy weight of 250kg.

A troop of ring-tailed lemurs were encouraged on to the scales by the offering of tasty treats, just one of the tactics used by zookeepers to entice the animals into being weighed and measured.

Each measurement is added to the Zoological Information Management System (ZIMS), a database shared with zoos all over the world.

Teague Stubbington, ZSL’s assistant curator of mammals, said: “We have to know the vital statistics of every animal at the zoo – from the tallest giraffe to the tiniest ant.

“It helps to ensure that every animal we look after is healthy, eating well, and growing at the rate they should – weight is a particularly important indicator of health and wellbeing.

“A growing waistline can also help us to detect and monitor pregnancies, which is so important as many of the species at ZSL London Zoo are endangered and part of international breeding programmes, such as Oni the okapi who is currently pregnant with her second calf.

“By sharing information with other zoos and conservationists worldwide, we can all use this knowledge to better care for the species we’re striving to protect.”