The broadcaster and naturalist is fronting a TV appeal to help save the conservation charity, which runs London and Whipsnade zoos.
The financial impact of coronavirus has left ZSL facing its biggest challenge in its near 200-year history, according to the organisation’s director general Dominic Jermey.
In the video appeal, Sir David said: “The Zoological Society of London has made an outstanding contribution to conservation and to our understanding of wildlife for 200 years.
“Today, ZSL’s work is vital in driving forward the vision of a world where wildlife thrives.
“Its two zoos, London and Whipsnade, are home to over 20,000 animals, many of which are endangered in the wild, from tiny dart frogs to majestic tigers and everything in between.
“ZSL now faces its toughest challenge to date. Put bluntly, the national institution is now itself at risk of extinction.”
The society, which was founded in 1826, has been forced to close its zoos to the public since the end of March, meaning it has lost income.
It marked the first time the zoos had closed since the Second World War.
Sir David 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 interactions with animals.
“Now, more than ever, we must support the work of this global conservation charity.”
The appeal will be shown on Sky channels from Thursday.
Mr Jermey said: “The closure of London and Whipsnade zoos put us under immense financial pressure.
“Our zoos may have been able to reopen their gates, but with strict social distancing measures and heavily restricted visitor numbers, we have no way of recouping what was lost; we’re fighting our biggest challenge in our 200-year history.”
He added: “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, 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.”
Zoos were able to reopen last month as lockdown restrictions were eased.
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