These are general principles on bat mitigation and compensation. They do not replace the need for using a suitably experienced ecological consultant and / or going through the relevant licensing procedures. Please consult the Bat Mitigation Guidelines for in-depth information.

Mitigation hierarchy

The overarching aim of ecological survey and assessment work used to ‘inform planning proposals is to minimize impacts, and to maximize benefits for biodiversity, as a result of the development’. The “mitigation hierarchy” is the accepted approach to enabling this to happen. Avoidance of any impacts should be the first consideration, the next step is then mitigation of any impacts that cannot be avoided, and lastly compensation should be used to off-set unavoidable remaining impacts.

Avoidance, Mitigation & Compensation

Definition and examples:

Avoidance refers to choosing options that avoid harm to bats or disturbance of their roost (for example, by retaining a roosting structure through the development design).

Mitigation refers to measures to protect the bat population from damaging activities and to reduce or remove the impact of development (for example. by carrying out works to a summer roost site when bats aren’t present in the winter).

Compensation refers to the offsetting of remaining impacts in the form of roost creation, restoration or enhancement as a result of loss of breeding or resting places (for example, by building a new roosting site when the original roosting site is lost through demolition of a building).

Enhancements refer to providing net benefits for biodiversity over and above requirements for avoidance, mitigation or compensation (for example, the creation of additional roosting sites above and beyond those required for mitigation and compensation purposes).

Mitigation and / or Compensation should allow conservation status of bats to be maintained or enhanced following development.

For clarity this site will use the term mitigation to encompass both mitigation and compensation.

Avoidance, Mitigation & Compensation

Hugh Clark


Avoidance is always the preferred form of mitigation. It involves steps taken to avoid deliberate killing, injury or disturbance to bats and to existing roosts.

Timing of works

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 impacting bats. Bats are their most vulnerable in buildings during the summer when large numbers are gathered for breeding and rearing young or in winter when they are hibernating. Evidence gathered through ecological assessment gauges species, type, size and seasonality of a roost to guide timing of works.

Retention of roosting site

By gathering ecological data about a bat roosting site at the start of development or maintenance works, it may be possible to ‘design out’ the impacts of a development by retaining the roosting site and building around it. Care should be given to ensure commuting routes to and from the roost are also retained and indirect impacts controlled for, such as the impact from the addition of artificial lighting.

Roost restored or created

If a roosting site cannot be retained in situ or will be modified by development or maintenance works, then the works must ensure the roost must be restored to its former roosting opportunities or recreated to mimic the roost lost.

Critical information should be gathered on the bat roost requirements to ensure this is possible, these include:

  • Access points
  • Roosting site, size and material
  • Temperature

Long-term habitat management and maintenance

Ecological data gathered on site will detail what habitats are being used by which bat species for a variety of essential behaviours; roosting, foraging and commuting.

These habitats should be maintained or recreated as part of the mitigation process, this will be guided by the ecological consultant and the data collected during surveys of the site.

Post-development population monitoring

This is an essential part of the mitigation process as it feeds back data into the system to assess firstly whether the mitigation is working and secondly if it isn’t, whether interventions are needed to adjust the mitigation implemented. This process should be guided by a suitably experienced ecological consultant using best practice guidance.

[1] BS 42020:2013 Biodiversity. Code of practice for planning and development (2013) British Standards