Bats and NIRAS’ work in Denmark

Langøret Flagermus MHES 2
Noel Anthony Damholdt Bergin

Noel Anthony Damholdt Bergin


This insight article delves into how the species protection under the Habitats Directive influences the daily life of biologists and experts on nature at NIRAS.

March 13, 2024

The 1992 Habitats Directive (92/43/EEC) deals with the conservation of habitats for animals and plants. The aim of the directive is to protect species and habitats that were vulnerable and rare in the EU and to ensure the long-term thriving of protected species and habitats in the EU.

The Habitats Directive has two pillars: (1) Site protection through the Natura 2000 network and (2) strict species protection. This species protection covers, among other things, breeding and resting areas for the "Annex IV species" and was first implemented in Denmark in 2007 (Habitat Order BEK 408-2007). Since then, the species protection of the Habitats Directive has become increasingly important in the environmental assessment of plans and projects in Denmark and the rest of the EU.

Increase in demand for assessments

In NIRAS, we have seen a strong increase in demand for assessments and mitigation measures in relation to the Annex IV species, not least bats. Whenever a project can affect buildings, trees or other habitats for bats, it is relevant to assess the impact more closely. If you look at NIRAS' project database with > 7000 active projects, bats are mentioned three times more often in 2023 than in 2020.

The increase is based, among other things, on customers' desire to avoid delays in construction projects, due to missing or inadequate assessments and studies of Annex IV species such as bats.

In NIRAS' project database, bats are mentioned three times more often in 2023 than in 2020.

If insufficient studies have been carried out, there is a risk of allowing new barriers in the landscape separating the areas where females and males live.

The complicated behaviour of bats

One might then ask why bats are vulnerable to disturbance?

Well, due to their ­high metabolism and social demands, they will often use a variety of rest areas, including both buildings and trees. A good example is one of Denmark's rarest bats – the Barbastelle (Barbastella barbastellus).

This species exhibits pronounced sexual segregation for most of the year, with males living alone (or in groups), often in areas where females ­never come. Males and females meet only to mate at special swarm sites in the autumn.

If insufficient studies have been carried out, there is a risk of allowing new barriers in the landscape separating the areas where females and males live. In this situation, the project (e.g. a busy road) may mean that the two sexes no longer meet and the population's opportunities to breed are lost, thus reducing the ecological functionality of the species.

The complicated behaviour described for Barbastelle bats varies between the 17 different bat species in Denmark. Although all species are covered by the same protection, it is often crucial to know which species exist in an area affected by a project. Therefore, in order to obtain sufficient knowledge in order to assess the consequences of a project, it is necessary to understand which species are present in the area, their numbers, and behaviour.

How a projects impact on bats are assessed

At NIRAS, the following steps are usually followed when assessing the impact of projects on bats: 

  • Desktop study: This study identifies potential habitats for bats that may be affected by the current project.

  • Habitat assessment: The habitat assessment examines structures in buildings, trees and other habitats. The survey identifies and assesses potential breeding and resting places (often called Potential Roost Features - PRF). The habitat assessment can be made in all seasons. Often, climbing equipment and endoscopes are used to examine holes and hollows in trees or buildings. During the examination it is sometimes possible to collect droppings or even carcasses from bats, from which the species can be determined with the use of eDNA.

  • Studies of occurrence and activity. These studies use advanced equipment (ultrasonic recorders and, where appropriate, cameras). Activity studies are carried out in two periods during the summer, when the bats are active, and species identification is assisted using their ultrasonic calls.

  • Description and execution of mitigation measures. Mitigation measures are used to replace breeding and resting areas and dispersal corridors that may be affected by a project. The mitigation measures may include, for example; veteranization of trees, installation of bat boxes, protection of existing trees and forests, planting of new hedgerows, and measures that limit the impact of noise and light.

It can take a lot of time and effort to carry out the necessary investigations and remedial measures for bats. However, if these are carried out correctly and with due care, then most projects can be implemented within the Habitats Directives framework of species protection, and the ecological functionality of Denmark’s bat species can be safeguarded.

Get in touch

Noel Anthony Damholdt Bergin

Noel Anthony Damholdt Bergin


Aarhus, Denmark

+45 4299 5495

Martin Hesselsøe

Martin Hesselsøe

Market Director (Nature & Biodiversity)

Aalborg, Denmark

+45 4097 9503