The myth of a grotesque vampiric beast – the chupacabra – said to terrorise the island of Puerto Rico in the Caribbean, and linked with UFO visitations and cover-ups, is exploded in a new book from Jonathan Downes, founder and director of the Devon-based Centre for Fortean Zoology.

Just how Jonathan, pictured below, achieves this – and comes up with a much more sinister explanation for happenings on the island over the past half-century (which I won't reveal for fear of spoiling the book for readers) – makes a compelling tale.

Puerto Rico has a long history of sightings of strange animals and Jonathan was first drawn there to investigate in 1998, returning in 2004, each time with film crews.

Attacks on farm animals had been attributed to the chupacabra – which translates as "goat-sucker" – since the mid-1990s. "The creature was described as being 4-5ft tall, walking semi-bipedally, and with a crest of strange spines down its back," said Jonathan, of Woolfardisworthy in North Devon.

"The whole thing got mixed up with the global alien mythos because Puerto Rico is a hotspot of UFO sightings and all sorts of other high strangeness. People put two and two together, as they always do, and came up with a number that certainly wasn't four.

"I think this book of mine is the first one to actually treat the chupacabra as a living, breathing creature. It isn't a vampire at all, but a species of animal that I believe is awaiting discovery in the high grassland plateau."

■The Island of Paradise: Chupacabra, UFO crash retrievals and accelerated evolution on the island of Puerto Rico is published by CFZ Press at £12.50.