Pipistrelle bat emergence

Bat active season has begun and our ecologists have turned nocturnal

Monday, June 3rd, 2019

May marked the start of bat active season and the recommended time window for dawn and dusk surveys. It’s time to contact our experts to book them in to visit your site.

The days are now noticeably longer, and the temperatures milder. As you’re drawn from your front room for an evening meal on the patio, bats too are emerging from their summer/maternity roosts for a night of foraging. As dusk and dawn surveys have begun our bat experts have put their 8 hours’ sleep behind them and have turned somewhat nocturnal themselves!

The period running from the beginning of May until the end of September is known in the industry as the ‘bat active season’ and is the optimal window for carrying out bat surveys to identify summer roosts and undertake bat activity surveys. The optimum period to identify maternity (breeding) roosts is mid-May to Mid-August.

If you have had your site assessed by a qualified ecologist and their assessment included one or more of the following:

  • a low, moderate or high potential for bat roosting
  • confirmed the presence of a summer bat roost in a tree or building
  • suitable habitat on the site and in the surrounding area for commuting and foraging

then you will require further surveys of your site to confirm the presence or likely absence of bats, characterise the activity and identify the type of roost and species. All with the aim of devising a mitigation strategy to help ensure your projects are a success as it navigates the planning system.

Now is the time for bat activity surveys

Emergence and re-entry – May to august

Shortly after sunset, bats begin to emerge from their roosts to feed before returning for the day shortly before sunrise. Bat roost emergence and re-entry surveys are therefore undertaken at dusk and dawn by suitably experienced bat ecologists who surround the structure in order to cover all possible exit and entrance points and record all emerging and re-entering bats, their flight paths, species and time of flight. The use of technology, such as infra-red or thermal imaging cameras can also assist the surveyors with pin-pointing bat emergence and re-entry locations.

The number of emergence/re-entry surveys required will be determined by the level the of assessed potential:

  • low: at least one survey;
  • moderate: two to three surveys spread out across the season;
  • high/confirmed: three spread out across the season.

Activity transect – April to October

Bats often use natural linear features such as edges of woodlands, hedgerows and rivers as corridors to commute from one location to another and reach their foraging areas from their roost sites. In order to provide a representative sample of bat activity within the project site, walked transect surveys can be utilised. These involve the surveyors following a transect route with a bat detector to evaluate if your proposed development may impact bat flight paths and identify key areas of bat activity which will inform the design of the development.

In order to supplement the “snapshot” of data collected during the transect surveys or emergence and re-entry surveys, automated ultrasound recording device bat detectors can be placed in various locations within the site and left for several days to gather information over time.

Advanced bat surveys – mid-May to mid-October

We have suitably qualified ecologists trained and licensed in harp-trapping and netting for bats to enable the capture of cryptic bat species and species that are woodland specialist and where standard survey techniques do not apply.

Harp trap set up for bats

We can also undertake radio-tagging and radio-tracking to identify bat roosts for species in complex areas such as woodland.

What level of mitigation is needed for your site and do you require a licence?

If as a result of these bat activity surveys it is concluded that bats are present a ‘mitigation strategy’ will need to be developed and included in the planning application. Our experienced and licensed ecologists can provide advice on mitigation methods. These may include the retention of bat roosts and foraging and commuting habitats, design modifications to building plans, advice on timing of works to minimise disturbance, and the provision of new habitats and roosts such as the erection of bat boxes/houses.

The results of the bat active surveys will inform which of the following levels of mitigation licence, if any, will be required for your site:

Mitigation class licence to allow low impact work on bat roosts (CL21)

To allow low impact work on bat roosts, a bat mitigation class licence will be required. This licence is held by a registered consultant and they must register the site before work starts. A number of our ecological consultants have this licence and can advise whether your site fits the bill.

Bat mitigation licence (A13)

If the development cannot avoid disturbance or other impacts to bats, a licence to carry out the proposed works must be obtained from the appropriate licensing body before development can take place. The work involved in this licence application is more complex than the low impact licence due to the higher impact on bats. Part of the process is ensuring appropriate mitigation measures have been designed and the project programme includes monitoring of the mitigation’s effectiveness. Our consultants have extensive experience of acting as the named ecologist on this type of licences and will do the application on your behalf.

Get in touch

Our experienced ecologists will work with you to help ensure your project can proceed in a way that complies with legal obligations, is cost and time effective, and minimises disturbance to bats and their habitats. We aim to make places better for people and wildlife.

Contact us now to book in your surveys and avoid any potentially costly delays to your development plans.

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