Researchers revealed that more than 96% of people have never seen a nightjar in the wild, and sightings of the nocturnal, silent flying, camouflaged birds are so rare that 5% of Britons believe them to be extinct.
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The 'Natural Curiosities Report' shines a spotlight on the native British species, which are rarely seen beyond the confines of animal sanctuaries and zoos.
Around 70% of British adults have never seen an adder in the wild, while 66% have never seen a dormouse and 61% a badger in the wild.
A quarter of British adults have never seen a wild hedgehog, and even the celebrated conservationist David Attenborough has never seen a pine marten in the wild.
The study was specially commissioned to mark the launch of the new television series of Mr Attenborough's Natural Curiosities on the digital channel Watch, which starts next Tuesday.
The presenter said: "This report shines a spotlight on some of the most curious and interesting species at large in the UK today. I have been lucky enough to see most of the animals listed in the wild, except for the pine marten, which are exceptionally hard to spot as they live up in the treetops.
"It is interesting to note that many of our supposedly common species are also hard to spot in the wild. The fact that a quarter of British adults have never seen a wild hedgehog suggests that we are witnessing rapidly dwindling numbers."
The research team, led by Dr Toni Bunnell, spent a month analysing reported animal sightings in order to collate a list of the 20 most elusive indigenous species, before 2000 British adults were asked whether they had ever seen any of them in their natural environment.
It is estimated there are 4606 pairs of nightjars in the UK, 3300 pine martens, and 442 pairs of golden eagles.
According to the RSPB, there are 431 pairs of golden eagles in Scotland but persecution means that they are confined to more remote areas of the country.