February 25, 2017, BBCA
The ploughshare tortoises were handed to Chester Zoo in 2012 after being confiscated by Hong Kong customs officials in 2009.
Regarded as the most threatened species of tortoise, say zoo bosses, they are native to Madagascar.
Dr Gerardo Garcia, of the zoo, said they were the "jewel in the crown of the reptile world".
Prized for their distinctive gold and black shells, they fetch "exceptionally high prices on the international black market", a spokesman said.
Efforts to steal the animals are so relentless there may only be 500 left, making it one of the rarest animals in the world, he added.
Dr Garcia said there was a "very real possibility the species could be lost forever due to illegal trafficking for the exotic pet trade".
"Most of these illegally exported tortoises are sold in markets in South East Asia," he explained.
The quartet were part of a shipment of 13 being smuggled from Madagascar and will form part of the European Breeding Programme for the species.
They are going on display at the zoo to raise awareness of the illegal exotic pet trade.
Worth £15bn ($19bn) a year, it is the fourth biggest international crime after drugs, arms and human trafficking, a zoo spokesman said.
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