Bat Roost Emergence/Re-Entry Surveys

When are Bat Roost Emergence/Re-entry Surveys Required?

Where the Bat Roost Potential Survey finds no potential for roosting bats, no further surveys will be necessary. However, where the Bat Roost Potential Survey identifies low, moderate or high potential/suitability for roosting bats further emergence/re-entry surveys will be required to confirm the presence or likely absence.

What is a Bat Roost Emergence/Re-entry Survey?

Bat Roost Emergence/Re-entry Surveys, sometimes referred to as ‘full’ bat surveys, involve the surveillance of all aspects of the building(s) or tree(s) according to the standard methods described by the Northern Ireland Environment Agency (NIEA) (available here) and the Bat Conservation Trust (BCT). This will normally involve a number of bat ecologists observing the building(s) or tree(s) for approximately 2hrs at dusk (a dusk survey) and/or for approximately 2hrs prior to dawn (a pre-dawn survey). A dusk and pre-dawn survey carried out within 24hrs counts as one survey visit.

To ensure complete surveillance coverage of the study building or tree a number of surveyors or viewpoints will be required. “Surveyors must be stationary to avoid bats being missed” (BCT Guidelines). For a small, square/rectangular building 2 surveyors or viewpoints should, therefore, be sufficient. However, where the building is larger or has a more complicated layout, additional surveyors or viewpoints are likely to be necessary to ensure complete surveillance coverage.

For trees, Potential Roost Features (PRFs) can be inspected by climbing the tree prior to further emergence/re-entry surveys. The benefit of this is that the number of emergence/re-entry surveys can potentially be reduced as many PRFs that appeared to have moderate or high suitability from the ground may, in fact, hold low or no potential, upon closer inspection. BCT also state that emergence/re-entry surveys are unlikely to give confidence in a negative result and tree-climbing bat surveys to inspect PRFs will be required in any case prior to felling or pruning works on trees.

The minimum survey effort required to establish an acceptable level of confidence in results relates to the overall bat roosting potential identified by the Bat Roost Potential Survey and is specified in the BCT Guidelines:

Cost: From £1,100*

Low Bat Roosting Potential:

1 Survey Visit for buildings (none required for trees) with sufficient surveyors or viewpoints employed to ensure complete surveillance coverage.

Cost: From £1,100*

Moderate Bat Roosting Potential:

2 Survey Visits for buildings and trees with sufficient surveyors or viewpoints employed to ensure complete surveillance coverage.

Cost: From £1,700*

High Bat Roosting Potential:

3 Survey Visits for buildings and trees with sufficient surveyors or viewpoints employed to ensure complete surveillance coverage.

Cost: From £2,400*

*NOTE: The costs quoted above may vary for larger or more complex sites or for greater travelling distances. All quoted figures are exclusive of and are subject to VAT.

The costs quoted above are based upon 2 surveyors providing sufficient surveillance coverage. Where more than 1 building is being surveyed or more than 2 viewpoints are required there may be savings in costs if visibility overlap can be achieved.

How long does a Bat Roost Emergence/Re-entry Survey take?

When considering the completion time required for Bat Roost Emergence/Re-entry Surveys it is important to bear in mind the following NIEA and BCT survey stipulations:

• All surveys must take place during the bat active season (May-Sep inclusive)
• At least one survey must take place during the peak of activity (May-Aug inclusive)
• Surveys must be distributed as far throughout the active season as possible.
• All surveys must be conducted during suitable weather conditions (not wet, windy or cold)

Upon appointment, we will provide you with a booking for a particular week but please remember that the specific date of your surveys will depend upon the weather! Final reports are usually available in approximately 2 weeks following the last survey. However, this may vary depending on how big the site is, how complex the layout is, the level of bat activity recorded and how busy we are.

What if roosting bats are found?

If roosting bats are found the proposed works may well have no impact upon them. However, if the impact assessment indicates that impacts are likely, an appropriate mitigation plan will need to be developed. This is very site-specific and the details will depend upon what is found on site and the specifics of the proposed works. Our ecologists will advise on the most appropriate, pragmatic and cost-saving solutions available.