The impact of ecological survey seasons on project timescales

16th December 2015

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  • Natural resources ,
  • Biodiversity ,
  • Ecosystems


Lee Daniels

Christopher Slater, environmental planner at TEP, clarifies when ecological surveys are required to inform EIA and what constraints can lead to delay.

EIA delivery can be significantly hampered if tight timescales prevent adequate ecological survey at the correct time of year for different types of wildlife. This article aims to provide more clarity on when surveys are required so that EIA managers are better informed and can discuss realistic timescales with clients.

The table below summarises the optimum survey periods for habitats and the most commonly encountered fauna for which surveys are undertaken. It is based on published guidelines for each survey type. It is easy to see that there is the possibility for ecological surveys to pose significant constraints on EIA and project timescales. The only exception are otters and badgers which can be surveyed year-round.

There can be some flexibility for surveying outside these periods and it is agreed with statutory consultees. For instance, a warm spring could mean that habitat, great crested newt or reptile surveys can be undertaken earlier than normal, or a warm autumn could extend the survey period for habitats, water voles and bat activity or roost surveys without damaging the quality of the survey data.

Surveying outside the optimal time could also be justified when aerial imagery indicates that the site contains habitats of low structural and species diversity with few features that could be used by protected species.

This can often be the case in urban areas. A justification for this has to be included within the resulting report and there is still a risk that planning consultees may request a repeat visit within the appropriate season.

Any change from standard survey guidelines must be justified by a clearly articulated reasoned professional judgement. This was shown in the recent Thornhill Estates case in Leeds (Bagley Lane/Calverley Lane, Farsley, Leeds application Ref: 12/04046/OT) with respect to bat survey intensity and interpretation of the Bat Conservation Trust's good practice guidelines on bat surveys.

When specific detailed habitat surveys are required there may be further seasonal constraints. For instance, if an area of woodland or potentially important hedgerows are likely to be affected by a development and require a detailed survey this can only be undertaken in April to June in order to record spring-flowering ground flora.

Conversely, detailed vegetation surveys for the majority of other habitats including heathland, uplands and saltmarsh are best undertaken in mid to late summer when the majority of the species assemblage is readily identifiable. There is a similar situation with invertebrate surveys, since many species are only active for short periods during spring to late summer. If a survey is required for a specific species, this will have to be timed to coincide with its active period. For example, this would be mid-April to late June for the grizzled skipper butterfly, a section 41 species of principal importance under the Natural Environment and Rural Communities Act 2006.

Even within the optimal survey period for particular types of wildlife, delays can occur due to poor weather, for example, nocturnal bat surveys are not advisable in rain and high winds. Warm, dry and calm weather is best for butterflies and reptiles.

Pond surveys for great crested newts previously have been constrained by the need to undertake four surveys between mid-April and June. The advent of eDNA testing now provides more flexibility since only one sampling survey is required within this time period. This can be useful if it has not been possible to complete surveys during the core mid-April to mid-May period, for example, due to a late commission, or where impacts are expected to be low, for instance, where ponds are distant from the development site. eDNA sampling can reduce the delays and financial burdens that can sometimes result from the seasonal restrictions of great crested newt surveys.

It is also important to bear in mind that some initial surveys often lead to the need for further detailed surveys. This is particularly the case with bats when for example, a roost assessment of trees or buildings undertaken in the spring leads to the need for three dusk emergence or dawn re-entry surveys which have to be undertaken between April and September.

Occasionally there is a requirement from statutory consultees for more than one season's data to be gathered, which can lead to significant extension to the timescales for surveys. This is most likely with winter bird surveys when a proposed development has the potential to affect species in special protection areas, a European designation.

These issues, combined with the constraints of specific survey periods for different types of wildlife, have the potential to delay the EIA process and the submission of planning applications. The best way to avoid this is to commission an ecological consultant to the project or EIA team as soon in the design process as possible. As EIA is an iterative process, ecological survey results can help inform the design of a development early on and avoid expensive and untimely redesign or mitigation later in the process.


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