Hazel dormice are a predominately arboreal species that can be found in well-connected habitats including hedgerows, scrub, and woodlands. Hazel dormice and their habitats receive European protection under The Conservation of Habitats and Species Regulations 2017 (as amended), and further legal protection under the Wildlife and Countryside Act 1981 (as amended) and Regulation 41 of the Habitats Regulations 2010. Hazel dormice are also listed as a species of principle importance under Section 41 of the Natural Environment and Rural Communities Act 2006 and are considered a material consideration within the planning process in accordance with the National Planning Policy Framework 2023. Combined, this legislation makes it illegal to deliberately disturb, kill, injure, or capture hazel dormice, as well as damage, destroy or obstruct any hazel dormouse habitats.
A Hazel Dormouse Presence/Absence Survey (HDPAS) is an assessment to determine whether hazel dormice are present within the existing habitats on site. This survey is usually recommended following a Preliminary Ecological Assessment (PEA), if development works are likely to disturb or remove suitable hazel dormouse habitat, such as woodland, scrub, and hedgerows. The aim of a HDPAS is to search for evidence of hazel dormice and determine which habitats on site are being used by hazel dormice, so that the potential impacts of the proposed development on hazel dormice can be assessed. HDPASs are required to inform avoidance, mitigation, compensation, and enhancement measures and a European Protected Species Licence (EPSL), if required, as part of the planning process. For Natural England to grant an EPSL, the project must be granted full planning permission. The EPSL application will need to be accompanied by a Method Statement, detailing mitigation measures for hazel dormice, and must be informed by the HDPAS.
HDPAS is a three-part process: a desk study, field surveys, and an evaluation/impact assessment, which are often presented in an Ecology Surveys Report.
A desk study involves identifying the habitats in the wider landscape and assessing their quality and connectivity to the habitats on site, so that the ecologist can assess both the likelihood of hazel dormice being present on site and in the wider landscape. Identifying whether any EPSLs for hazel dormice have been granted in the wider landscape can be useful information as this highlights that hazel dormice are known to be present in the area.
Field surveys involve an ecologist, with at least a Class 1 Hazel Dormouse Survey Licence, visiting the site to search for evidence of hazel dormice. Permission from the landowner and a full risk assessment are required prior to field surveys.
A minimum of 50 nest tubes are deployed in suitable habitats at approximately 20 m intervals, in accordance with best practice guidelines (Chanin and Woods, 2003). For large sites, over 50 nest tubes may be necessary to competently cover the suitable habitats. Once deployed, the nest tubes need to remain in situ until all survey visits are completed. All management of the habitat where the nest tubes are situated, including flailing, coppicing, and felling, must cease until all survey visits are completed. This is because the management of the habitat could disturb or discourage hazel dormice from being present and therefore invalidate the findings of the survey. Once deployed, the nest tubes are not inspected for a least a month, to allow them to bed into the habitat.
The nest tubes are inspected monthly by a licenced ecologist to search for evidence of hazel dormice such as the nests and the hazel dormice themselves. Where any hazel dormice are found, the gender and life-stage are recorded, where possible. Nest tube inspections are undertaken using a torch or by sliding the trays open.
The number of visits (excluding the initial deployment visit) must abide by survey effort requirements, using an Index of Probability, in accordance with best practice guidance (Chanin and Woods, 2003) (Bright et al., 2006). The Index of Probability provides a score for each month assuming 50 nest tubes have been deployed at least 20 m apart. The scores for each month are based on how likely evidence of hazel dormice are found in the nest tube. The Survey Effort Score must add up to at least 20. If a minimum Survey Effort Score of 20 has been achieved and no evidence of hazel dormice has been recorded, then it can be reasonably assumed that hazel dormice are absent from the site.
Month | Index of Probability |
April | 1 |
May | 4 |
June | 2 |
July | 2 |
August | 5 |
September | 7 |
October | 2 |
November | 2 |
As well as inspecting the nest tubes, the ecologist will also carry out a nut hunt, where ecologists search for hazel nuts that have been chewed by hazel dormice. If a hazel nut chewed by a hazel dormouse is found this will be enough evidence to prove presence on site.
With the information from the desk study and field surveys, the ecologist will then carry out the evaluation assessment to assess the level of impact the development will likely have on hazel dormice and their habitats. The assessment will include any avoidance, mitigation, compensation, and enhancement measures and whether an EPSL is required. The reports are written in accordance with the up-to-date CIEEM guidelines for ecological report writing and are valid for 12 months. Updated surveys may be required if the report is not submitted as part of a planning application within 12 months.