The persistent rain over the last few months has hit the animals hard. Unable to find enough insects, mothers have had to abandon their babies because they cannot produce the milk to feed them.

Dr Graham Hopkins, an insect expert and founder of the Norwich Bat Group, said the creatures were facing a tough time. The 37-year-old from Matlock Road said: "Bats only produce young once a year, so orphaned animals mean there won't be another baby from that mother this year. If this happens more than once, it could mean a problem for the population."

The group has been researching bats in the city and has found more than three species in Norwich. Lion Wood in Thorpe Hamlet is a favourite site for the creatures.

Despite common misconceptions, the animals are vital in the food chain to keep down the level of insects.

Dr Hopkins also said they cause no harm to properties if they live in roofs - although advances in cavity insulation mean bats are struggling to find new places to live.

He said: "New houses are so well sealed there is nowhere for them to go. Most live in houses from the 1970s or 80s."

Evidence is also mounting that wind turbines are killing bats.

Louise Oliver, of the Norfolk and Suffolk Government Team from Natural England, is working with the bat conservation group. Their research has found people with wind turbines often find dead bats near the machinery first thing in the morning.

She said: "It's possible because of the heat generated by wind turbines, insects fly near them to feed and are hit by blades. However, we don't yet understand why bats are the only animals affected.

"We are hoping to encourage people to turn them off at night to solve the problem, and also would like people to contact us if they find a dead bat."

# To contact the bat group, call Dr Hopkins on 01603 660300. Call Louise Oliver on 01603 598400.

# Have you started an animal group? Call Lucy Bolton on 01603 772429 or e-mail lucy.bolton@archant.co.uk