"He's gone," murmurs Chester Zoo vet Gabby Drake - holding a stethoscope to the feathered chest of a 28-year-old, bright red tropical parrot.
The bird is a chattering lory - an elderly resident at Chester Zoo, and a species listed by the International Union for the Conservation of Nature (IUCN) as vulnerable to extinction.
It is sad to see this striking, characterful bird having to be put to sleep. His small, clawed feet are gnarled with arthritis now too severe to treat.
It is not the end though for the unique genetic code contained in his cells. A few small pieces of his body will join samples taken from 100 species. They will be frozen - stored indefinitely - in the UK's largest biobank of living tissue, Nature's Safe.
In vials of a nutrient-rich, cell-friendly antifreeze, the samples are kept at -196C, at which point all the natural chemical processes in cells stop - they are suspended in animation.
The idea is that, at some point in the future - in decades, perhaps even centuries, they could be resurrected. This is a frozen backstop in case of extinction.
Life begins again
Conservationists say we're now losing species faster than ever. Amid a biodiversity crisis that, the UN estimates, threatens one million species of plants and animals with extinction, some scientists are now working out what to put in the freezer for the future.
"It's not going to stop extinction, but it'll certainly help," says Tullis Matson, founder of Nature's Safe.
Tullis is a tall, friendly and outspoken enthusiast for his charity's mission - preserving living tissue from wild animals.
"This is where life begins again," he beams, showing me an image of a vial of cheetah skin cells under the microscope.
The monitor is teeming with densely packed skin cells - a body's building blocks. The black dot in the middle of each spiky, connected cell is a nucleus containing a unique set of genetic instructions that made, in this case, a now deceased cheetah.
"This animal died in 2019," Tullis explains. "We woke up those cells a few days ago - and you can see now, they're all over the screen. They've multiplied and multiplied."
Skin cells are very good for this endeavour, particularly a type of connective tissue cell called a fibroblast. These are critical to healing and repair and - after being removed from the freezer and warmed to body temperature in a bath of necessary nutrients - will divide and multiply beautifully in a dish.
One of the possible future uses for these cells is cloning new animals, using these defrosted packages of DNA.
Cloning animals is not new. It was 1996 when scientists in Scotland cloned Dolly the sheep - fusing a cell from one ewe with the egg of another. It is reproductive technology, born in the realm of domestic animals and now being channelled into conservation.
US biotechnology company Revive and Restore recently produced a clone using skin cells from an endangered black-footed ferret that had been dead for decades. Its eggs were frozen in 1988.
Fusing a ferret fibroblast with an egg cell made an embryo, and a clone - Elizabeth Ann the black-footed ferret - was born in December of 2020.
They used same basic approach to clone a Przewalski's horse - a species considered the last living truly "wild" horse at a cost of $60,000 (about £48,000). The clone, named Kurt, lives at San Diego Zoo.
"It was actually cheaper for the zoo to clone a horse - to bring more genetic diversity into the American population of the species - than it would have been to ship a horse from a European zoo," explains Revive and Restore's lead scientist Dr Ben Novak.
What species should we freeze?
Genetic diversity is important. As the population of a species dwindles, it can lead to inbreeding. In mammals, offspring have a set of genetic instructions from each biological parent. And if those parents are related, any genetic diseases they have are much more likely to be passed on.
Banking cells though is not about the cheapest way to resurrect genes, says Dr Novak.
"Conservationists are fighting to save species, but we've been unable to save everything - the destruction is ongoing.
"Getting out ahead and getting things in the bank gives us the opportunity in the future to do restoration," he says. "If we don't do this, we'll regret it later."
There could be a danger that biobanking sends the message that we don't need to worry about saving species now "because we can freeze them for later," points out Prof Bill Sutherland, a conservation biologist from the University of Cambridge.
"And there's the issue of prioritising what is stored," he says. "It would be wonderful to get tissue from 20 snow leopards from 20 different locations, but that would be really difficult."
Instead, Nature's Safe works closely with zoos in Europe - particularly Chester Zoo.
Whenever an animal has to be put to sleep or dies unexpectedly, zoo vets will take some tissue for the bank.
"It's a ray of light," says Tullis. "That animal dying actually gives a bit of hope for the future of that species, because we can freeze those genetics."
While banking what is available is not a perfect approach, it has provided Nature's Safe with samples from species including the mountain chicken frog - a critically endangered amphibian almost wiped out by a fungal disease. And it has tissue from a Javan green magpie, a bird driven to the very brink of extinction by demand from the wild bird trade. (The almost garishly beautiful birds have remarkable, and highly sought after mimicry skills).
Head of science at Chester Zoo, Dr Sue Walker, says it's about saving as much genetic material as possible. "If we don't do it when that animal passes way, we've just lost it," she says.
Earlier this year at Chester, Goshi, a nine-year-old female jaguar, was found dead in her enclosure. Vet Gabby Drake carefully snipped off the big cat's left ear, put it in cold packaging and posted it to Nature's Safe, before sending Goshi for a post mortem.
"Jaguars are not the most critically endangered big cats, but they're in decline and they're facing the same human pressures as other big predators," says Gabby.
"She was quite a young animal and she never had any cubs, unfortunately. It's sad, but it's nice to know that her living tissue will carry on."
Now, a few pea-sized pieces of Goshi's black, velvety ear - cleaned, prepared and bathed in a protective nutrient solution - are in an increasingly biodiverse canister of liquid nitrogen.
Tullis is optimistic about what science might be possible in the future. "With gene editing technology, we might even be able to create new genetic diversity," he speculates.
Looking at the now solo male jaguar patrolling his enclosure, Chester Zoo's Dr Sue Walker says it might be "decades until we have the technology to do what we want to do with these samples".
Her hope, and the hope of most conservationists, is that using frozen cells from long-dead animals will never be necessary.
"But if we don't collect it, then those genetics are lost forever," she says. "We've lost all that unique biodiversity."
Hear more from Victoria's investigation into biobanking on Inside Science on BBC Sounds
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