The rare Bechstein's bat is one of 13 bat species found in the New Forest
Experts and volunteers are undertaking a survey of the New Forest to record as much of the wildlife in the national park as they can in 24 hours.
Dubbed a BioBlitz, the event is being led by the National Park Authority and begins from 1500 BST on Friday.
The data collected will be used by the authority to decide how it can best look after the wildlife in the park.
Local residents and schoolchildren are taking part to find and record plants, fungi and animals.
'Rarer than rainforest'
Experts from the Natural History Museum, Hampshire County Council, Forestry Commission and the Hampshire Wildlife Trust will work with the park authority's tree officer, ecologist and bird expert.
Hilary Makin, spokeswoman for the national park authority, said: "The New Forest is a fascinating mosaic of habitats.
"It is primarily heathland which is more rare than rainforest, has some species which are only found in this area, has the highest concentration of protected wildlife sites of any of the English national parks and is home to 13 out of 17 of the UK bat species, so we are hoping to record some great results."
The BioBlitz includes a bat hunt, dawn chorus, beach safari, school bug hunt and live
so people can follow at home.
The New Forest has 61 sq miles (158 sq km) of heathland and about 700 species of wildflowers - nearly a third of the total found in Britain, Ian Barker, the authority's ecologist said.