Naturalist and broadcaster David Attenborough on Thursday warned the coronavirus crisis could kill off the world's oldest zoological society, along with the London Zoo and the animal conservation projects it supports worldwide.
The Zoological Society of London (ZSL) was founded in 1826, runs both London Zoo and Whipsnade Zoo north of the capital, and supports conservation projects in more than 50 countries.
But the zoos, home to some 20,000 animals, were shut for three months under a nationwide lockdown, and visitor numbers are now restricted because of social distancing guidelines.
Attenborough, 94, praised ZSL's "outstanding contribution to conservation and to our understanding of wildlife", and said many of its animals, from dart frogs to tigers, are endangered.
"ZSL now faces its toughest challenge to date. Put bluntly, the national institution is now itself at risk of extinction," he warned in a new campaign appeal video.
He added: "Without your help we could see the closure of the world's oldest scientific zoo, the place where generations of people have forged a love of wildlife through their joyful encounters with animals."
ZSL director general Dominic Jermey said the closure of the zoos "put us under immense financial pressure" at a time when its research could be vital.
"As well as educating and inspiring millions of people to make a difference for wildlife, we're at the forefront of research to understand how diseases such as coronaviruses transfer from wildlife to humans," he said.
"And we're using our expertise to help find new ways for humans and wildlife to peacefully co-exist. The world cannot afford for our work to be stopped; but we need help to keep going."
London zoo had 1,133,952 visitors in 2018, the 28th most popular British visitor attraction, according to ALVA, a tourism industry body.
Whipsnade received 608,416 visitors in 2018, the 61st most visited attraction.