Yorkshire Water planned to demolish the former dam-keeper's lodge at Linley Wood Reservoir, in North Yorkshire.

However, the proposals were abandoned when the pipistrelle and brown long-eared bats were discovered roosting in the roof.

The company now plans to fill in the ground floor of the cottage and keep the bats' base intact above water level.

Bat facts

Bats can live up to 30 years Of 4,500 mammal species in the world, nearly 1,000 are bats The pipistrelle is Britain's most common bat and weighs less than a two-pence coin Bats are not blind, but can "see" in the dark via high frequency calls

Engineers working at the reservoir at Otley discovered the bats when work started to raise the dam.

A spokesman for Yorkshire Water said: "When the bats were found, we applied for a bat licence to the government, because bats are a protected species.

"We are not allowed to disturb the bats more than necessary during the work. The work that we will have to do will be carried out through a small 'window'."

All bats in Britain are protected, but the pipistrelle and brown long-eared are not threatened.

The pipistrelle is the smallest bat in Britain and can catch up to 300 insects a night.

Woodland roost

The Bat Conservation Trust has praised Yorkshire Water's efforts to keep the colony's home safe.

A spokesman said: "It is great that the bats' interests are being taken into account on the reservoir.

"They like to roost near woodland and where there are plenty insects. It is difficult to say how long the bats have been there - or how long they will stay.

"Sometimes a colony will keep using the same place to nest."