Considering the Likley Presence of Bats

Surveys are needed to consider the likely presence of bats if there are structures on site that are likely to be affected by the development proposals.  The level of survey is still very much dependent upon the specific site conditions, development proposals and the Local Planning Authority. 

In most situations a bat habitat suitability assessment and survey is a minimum requirement.  This is a daytime survey that can generally be undertaken at any time of year.  The bat habitat assessment survey considers the suitability of structures to support bats based on the presence of suitable roosting opportunities (access, cracks, crevices etc); and, also the likely presence of bats based upon evidence of presence (droppings, feeding remains, staining, bats themselves etc) and the structures ecological context (proximity to suitable foraging and commuting habitat, lighting etc).

Further emergence and swarming bat surveys are likely to be required pre-planning in the following situations:

  1. Bat presence is confirmed
  2. There is medium/high likelihood of bats being present (despite no evidence)
  3. Access constraints during the bat habitat suitability assessment and survey


Where bat presence is confirmed the emergence and swarming bat surveys are required to confirm the species of bat using the roost and the number of bats present.  This information will then inform an assessment of the status of the roost.  The status of the roost and species present is required to assess the impacts of the proposal and determine specific mitigation requirements in order to maintain favourable conservation status of the bats.  Where bat presence has not already been confirmed these surveys enable further consideration of the likely presence.  Emergence and swarming surveys are weather dependent and can only be undertaken when bats are active, with the optimal survey season being between May and August (surveys at other times may be possible subject to specific site circumstances and weather conditions).

Where bat presence is unlikely or there is low likelihood of presence it is often possible to avoid further surveys  pre-planning (depending on the Local Planning Authority and specific site conditions).  In instances of low likelihood works may need to follow a Precautionary Method of Working, which may include further surveys immediately prior to works being undertaken that affect the structure.  It should be noted that identifying bats or evidence of bats shortly before or during construction can result in high expense as a result of works having to stop and potentially significant delays.  Therefore it is advisable to undertake some surveys in advance of works to minimise such risks. 

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