There are more than 115 Barbastelle bats living in a single tree
The Isle of Wight is Europe's most important woodland bat habitat, the Forestry Commission has claimed.
Two of the UK's rarest species - the Bechstein's and Barbastelle bats - have been found in woodland areas including Parkhurst Forest, near Newport.
A study found more than 20 maternity roosts on the island, compared with one in the whole of the UK in 1998.
One split ancient oak in the forest is thought to be home to 115 Barbastelle bats.
It is thought to be the largest single maternity roost for the species in the country.
Forestry Commission ecologist Jay Doyle said: "It came as a pleasing surprise that this study found the bats to be much more widely distributed than was previously thought."
The Forestry Commission introduced its Woodscape programme in 2001, a scheme which aims to rejuvenate the island's woodlands.
Parkshurst Forest is also a haven for red squirrels and woodpeckers and is the last known habitat of the rare pearl-bordered fritillary butterfly on the island.