Five endangered monkeys were stolen from an East Sussex zoo over the weekend, the latest in a recent string of small-monkey thefts across England, police confirmed Monday.

A family of Silvery Marmosets — a male, female and 2-month-old baby — and a pair of Geoffrey Marmosets were pocketed late Saturday night after thieves smashed into their cages at Drusillas Park Zoo, snatching them out of their nesting boxes. The burglars tried but failed to break into a third small-monkey enclosure, zoo officials said.

Zoos in Devon and Suffolk have also had small monkeys pilfered in recent weeks.

"This is not a casual crime," said John Haywood, coordinator of the National Theft Register for Exotic Animals. "This is extremely well-organized, and is no doubt part of a series — these are specialist crimes."

Haywood, who is working with law enforcement to crack the cases, said that police believe the Sussex monkeys were stolen to feed into the international illegal pet trade, as the stolen marmosets were captured in breeding pairs.

"We think they may have been taken to an illegal breeding station somewhere, with the intent of selling them abroad, across Europe," he said.

Small monkeys in particular have been targeted, he said, with over 50 stolen in England and Scotland over the past few years.

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Drusillas Park Zoo spokesman Ian Flamank said the East Sussex marmosets were estimated to be worth between $3,700 and $5,500 each.

Because small monkeys can be successfully bred in captivity, their profit-garnering potential is great — but their quality as pets is not, he said.

"They're great — behind glass," he said. "But they wouldn't make great pets. They're not companion animals."

Adult Silvery Marmosets weigh less than a pound and rarely exceed a foot in length, while the Geoffrey variety are a little larger.

Jazz, the mother in the Silvery Marmoset family, has a serious jaw condition and could die without medication, Flamank said. Her baby Larkin is similarly unstable, having only just been weaned.

"There's always hope — we'd really like to hold out for them to come back," Flamank said.