Avoiding damage to existing roosts is always the preferred option. This involves taking steps to avoid killing, injury or disturbance to bats and damage to or loss of their roosts.

Although not covered in detail here, please note that ecologist supervision and surveys immediately prior to development works are all essential parts of mitigation.

Timing of works

The most effective method of avoidance is to carry out the work at an appropriate time of the year when bats are absent.

The great majority of roosts are used only seasonally so there is usually some period when bats are not present and works can occur without adverse impacts on bats. For example, bats are particularly vulnerable in buildings during the summer when large numbers are gathered for breeding and rearing young. Works affecting known breeding sites, where baby bats are born or reared, should therefore be timed to avoid the summer months.

Generally, the best times for building or re-roofing operations will depend on how and when bats use a building.

Optimum season for works in different types of roosts:

  • Maternity roosts (where baby bats are born and reared): 1st October to 1st May
  • Summer roosts (where bats are present but without dependent young): 1st September to 1st May
  • Hibernation roosts (places which bats depend on during winter months): 1st May to 1st October
  • Mating/ swarming roosts (sites used by bats for important socialising and mating in late summer and autumn): 1st November to 1st August