Why Are Ecological Surveys Seasonal? A Guide for Developers

If you are planning a development, you may be advised that an ecological survey needs to take place at a certain time of year. 

Why can’t an ecological survey simply be carried out whenever a planning application is ready to submit?

Different species and habitats are easier to detect or survey at different times of the year. Some protected species are only active during certain seasons, while vegetation and habitats can be much easier to identify during periods of active growth.

As a result, leaving ecological surveys until the last minute can sometimes delay a planning application.

Why are ecological surveys seasonal?

Ecological surveys are designed to collect reliable information about the habitats and species that could be affected by a development.

Many species change their behaviour throughout the year. For example, bats are active during the warmer months, great crested newts spend part of their annual cycle in ponds, and birds have distinct breeding and wintering periods.

Weather conditions can also affect whether a survey is suitable. Some surveys require particular conditions to ensure that species can be detected reliably.

Natural England’s guidance provides indicative survey periods for a range of protected species, but the appropriate timing depends on the species, the purpose of the survey and the conditions on site.

This is why an ecologist may recommend that a survey is carried out during a particular season rather than immediately.

Bat surveys

Bats can be relevant to developments where buildings, trees or other structures could provide potential roosting opportunities, or where habitats could be important for commuting and foraging.

Different types of bat survey have different timing requirements.

Natural England’s guidance indicates that:

• Preliminary roost assessments can be carried out at any time of year, although trees can be easier to assess when they are not covered by foliage. 
• Surveys for summer bat roosts are generally carried out between May and August.
• Surveys of bat activity, including commuting and foraging behaviour, are generally undertaken May – September. Depending on what the suitability class is (ie Low, Medium, High suitability)
  Low roost suitability (May – August).
  Moderate roost suitability (May – September) With at least one of the surveys carried out between May and August.
  High roost suitability (May – September) With at least two of the surveys carried out between May and August.
• September surveys are both weather and location-dependant.
• Surveys relating to hibernation roosts are generally carried out between November and mid-March.

The level and type of bat survey required will depend on the site and the potential for bats to be affected.

This means that a preliminary assessment can be particularly useful early in the planning process. It can identify buildings, trees or other features that may require further investigation before development begins.

GCN

Natural England currently gives an indicative survey period of mid-March to mid-June for great-crested newt surveys using bottle trapping techniques. Environmental DNA (eDNA) surveys have a slightly different window, generally mid-April to the end of June.

Breeding Birds

Wintering bird surveys and migration surveys have different timing requirements. Natural England’s guidance identifies October to March for winter behaviour.

The migratory bird survey window in the UK typically runs from August to November for autumn migration and from November to March for the core wintering period. During this time, bird populations are actively moving, and any potential impacts on these species must be carefully considered.

• Autumn Migration: Birds are arriving in the UK for winter, departing for warmer regions, dispersing after breeding, or passing through on longer journeys.
• Core Wintering Period: This period is crucial for assessing the impact of developments on bird populations and habitats.
  

It is essential to conduct surveys during these periods to ensure compliance with UK wildlife protections laws and to avoid legal breaches. Professional ecologists can provide bespoke survey programs that incorporate all necessary surveys types and methodologies, taking into account site-specific geography, bird populations, and habitats in the area

Reptile surveys

Reptile surveys are generally carried out during the warmer months when reptiles are active.

Natural England’s indicative survey period is April to September. The best months for reptile surveys are typically from April to September, with the most productive months being April and May when reptiles are most active. 

Suitable habitat can include areas such as rough grassland, scrub, field margins, heathland and woodland edges.

If a Preliminary Ecological Appraisal identifies suitable reptile habitat that could be affected by a development, further survey work may be recommended.

Why should developers start ecological work early?

One of the biggest problems with seasonal surveys is  timing.

A developer may be ready to submit a planning application, only to discover that a required protected species survey cannot be completed for several months.

Starting with an initial ecological assessment can help identify potential constraints at an early stage.

A Preliminary Ecological Appraisal (PEA) can assess the habitats present on or around a site and identify features that may require further investigation.

Depending on the findings, this could lead to recommendations for surveys such as:

• Bat surveys
• Great crested newt surveys
• Reptile surveys
• Badger surveys
• Habitat and botanical surveys

Not every development will require all of these surveys. The appropriate survey effort should be based on the individual site, the proposed development and the potential ecological impacts.

Planning ahead can help avoid delays

Ecological surveys are an important part of many development projects. Different species and habitats have different survey requirements, and suitable survey periods can be affected by weather and site conditions.

Starting the ecological assessment early gives developers more time to identify potential issues, arrange any necessary surveys and incorporate ecological considerations into the design of the development.

If you are planning a development, consider your ecological requirements as early as possible.

Early advice can help establish which surveys may be needed and whether any of them are subject to seasonal restrictions.

ACJ Ecology provides ecological surveys and assessments to support development and planning applications. Our team can help identify potential ecological constraints and advise on the surveys that may be required for your project.

Get in touch: Enquiries@acjecology.co.uk