Wales and England

Ecological survey calendar

When to survey for protected species and habitats, when wildlife is most sensitive to works, and the best windows for clearance and mitigation. Turn the wheel to any month, or pick a species group for the detail.

In season

The year at a glance

Every survey season, sensitive period and works window, in half-month steps.

Optimal survey season Survey possible, not ideal Sensitive period Works window

Species guides

Background, key dates, legal protection and licensing for each group, with practical tips for programming works.

Bats

Order Chiroptera

Bats move between different roosts through the year: maternity roosts in summer, mating sites in autumn and cool, stable hibernation sites in winter. A building, bridge or tree can matter in one season and be empty in another, which is why survey timing matters so much.

Key dates, protection and tips

Key dates

  • Roost surveys (emergence and re-entry)Survey: May to Aug; Sep (not ideal)The number of surveys depends on roost suitability. At least one should fall between May and August.Source: Collins (2023)
  • Activity surveys (transects and static detectors)Survey: Apr to OctVisits spread across spring, summer and autumn. The number depends on how suitable the habitat is for bats.Source: Collins (2023)
  • Preliminary roost assessmentSurvey: All yearCan be done in any month. Droppings and staining are easiest to find in summer.Source: Collins (2023)
  • Hibernation surveysSurvey: Dec to FebChecks of known or potential hibernation sites while bats are torpid. Natural England's standing advice gives November to mid-March.Source: Collins (2023); Natural England standing advice
  • Maternity seasonSensitive period: May to AugFemales gather to give birth and raise young. Avoid disturbing roosts.Source: Collins (2023)
  • Hibernation seasonSensitive period: Nov to MarBats are torpid and easily harmed if disturbed.Source: Collins (2023)
  • Tree felling and roost worksWorks window: Sep to OctBetween the maternity and hibernation seasons. Late March to April is also used, but clashes with bird nesting. Exact timing is set by survey results and any licence.Source: BCT woodland guidance

Legal protection

All UK bat species are European protected species under the Conservation of Habitats and Species Regulations 2017. They are also protected by the Wildlife and Countryside Act 1981.

Licensing

Wales: Works affecting a roost need a European protected species licence from Natural Resources Wales, normally applied for after planning permission is granted.

England: Works affecting a roost need a Natural England mitigation licence, or registration under the Bat Mitigation Class Licence for qualifying low-impact cases.

Practical tips

  • Book emergence surveys early. The May to August window fills fast, and missing it can delay a planning decision by most of a year.
  • A preliminary roost assessment can be done in winter, so the right number of summer surveys can be planned in good time.
  • External lighting can affect bats as much as demolition. Plan it to ILP and BCT Guidance Note 08/23.

Badger

Meles meles

Badgers live in social groups in setts dug into banks, woodland edges and hedgerows. Cubs are born underground in late winter and stay below ground until spring.

Key dates, protection and tips

Key dates

  • Sett surveysSurvey: Feb to Apr; May to Sep (not ideal); Oct to Nov; Dec to Jan (not ideal)Possible all year. Easiest when vegetation is low and badgers are active.Source: Harris et al. (1989)
  • Breeding seasonSensitive period: Dec to JunCubs are underground. Sett interference is not normally licensed in this period.Source: NE and NRW badger licensing guidance
  • Licensed sett closureWorks window: Jul to NovThe period in which licences for sett closure are normally issued.Source: NE and NRW badger licensing guidance

Legal protection

Badgers and their setts are protected under the Protection of Badgers Act 1992.

Licensing

Wales: Interference with a sett needs a licence from Natural Resources Wales.

England: Interference with a sett needs a licence from Natural England.

Practical tips

  • Find setts before fixing a site layout. Buffers around active setts can shape a scheme.
  • Use trail cameras to show which entrances are in use before applying for a licence.

Birds

Class Aves

Most nesting happens in spring and early summer, but some species start in February and others carry on into September. A nest check by an ecologist is the safeguard whenever vegetation or structures are cleared.

Key dates, protection and tips

Key dates

  • Breeding bird surveysSurvey: mid-Mar to mid-Jul; mid-Jul to Aug (not ideal)Six visits spread evenly from late March to early July, starting around dawn, with at least one evening visit. Later visits suit some species.Source: Bird Survey Guidelines (2022)
  • Wintering bird surveysSurvey: Oct (not ideal); Nov to Feb; Mar (not ideal)At least monthly visits November to February, adding October and March where passage birds matter. Time coastal visits to the tides.Source: Bird Survey Guidelines (2022)
  • Nesting seasonSensitive period: Mar to AugSome species nest outside these months, so a nest check is needed before clearance at any time of year.Source: Ecoleg house standard
  • Vegetation clearanceWorks window: Sep to FebOutside the main nesting season, with a nest check within 48 hours before works.Source: Ecoleg house standard

Legal protection

All wild birds, their active nests and eggs are protected under section 1 of the Wildlife and Countryside Act 1981. Schedule 1 species are also protected from disturbance while nesting.

Licensing

Wales: No licence is available to remove active nests for development. Survey work near Schedule 1 nests needs a licence from Natural Resources Wales.

England: No licence is available to remove active nests for development. Survey work near Schedule 1 nests needs a licence from Natural England.

Practical tips

  • Clear vegetation between September and February wherever you can.
  • Ecoleg's standard is a nest check no more than 48 hours before clearance. An active nest stops work nearby until the young have fledged.

Great crested newt

Triturus cristatus

Britain's largest newt breeds in ponds in spring and spends most of the year on land, sheltering and hibernating in grassland, scrub, woodland and rubble. Surveys happen at the pond, but impacts often happen on land.

Key dates, protection and tips

Key dates

  • Pond surveys (presence or absence)Survey: mid-Mar to mid-Apr (not ideal); mid-Apr to mid-May; mid-May to mid-Jun (not ideal)Four visits for presence or absence, six for a population estimate. At least half between mid-April and mid-May, on nights above 5°C.Source: English Nature (2001)
  • eDNA water samplingSurvey: mid-Apr to JunSamples are taken between 15 April and 30 June. In Wales a negative result may not be accepted on its own, for example near known records or in pond-rich areas.Source: Biggs et al. (2014); NRW eDNA guidance
  • Habitat Suitability IndexSurvey: Mar to Jun; Jul to Feb (not ideal)Possible all year. Easiest to judge in spring when ponds are full.Source: ARG UK (2010)
  • Breeding season in pondsSensitive period: Mar to JunAdults and eggs are in ponds. Avoid pond works.Source: English Nature (2001)
  • Hibernation on landSensitive period: Nov to FebNewts shelter underground. Avoid ground disturbance in terrestrial habitat.Source: English Nature (2001)
  • Trapping and exclusion fencing (licensed)Works window: Mar to OctCapture only when night temperatures are above 5°C, under licence.Source: English Nature (2001)

Legal protection

European protected species under the Conservation of Habitats and Species Regulations 2017.

Licensing

Wales: Works likely to affect newts or their habitat need a European protected species licence from Natural Resources Wales.

England: Works need a Natural England licence, or can use District Level Licensing where the local authority runs a scheme.

Practical tips

  • eDNA sampling is quick but only valid from mid-April to the end of June. In Wales, NRW may still want traditional surveys behind a negative result, for example near known records or where there are many ponds.
  • Plan pond surveys before March so the season is not missed.

Reptiles

Common lizard Zootoca vivipara, slow-worm Anguis fragilis, grass snake Natrix helvetica, adder Vipera berus

Reptiles bask on sunny, sheltered edges such as rough grassland, scrub margins, banks and railway corridors, and hibernate underground through the winter.

Key dates, protection and tips

Key dates

  • Presence or absence surveys (refugia)Survey: Mar (not ideal); Apr to May; Jun to Aug (not ideal); Sep; early Oct (not ideal)Seven visits in suitable weather, roughly 9 to 18°C, avoiding hot midday sun. Natural England's season ends in mid-October.Source: Froglife (1999); Natural England standing advice
  • HibernationSensitive period: Nov to FebAvoid ground works in banks, rubble and tree roots that could hold hibernating reptiles.Source: Froglife (1999)
  • Two-stage habitat clearanceWorks window: Apr; Sep to mid-OctWhile reptiles are active and can move away. Spring clearance must also allow for nesting birds.Source: common professional practice

Legal protection

The four widespread reptiles are protected from killing and injury under Schedule 5 of the Wildlife and Countryside Act 1981. Sand lizard and smooth snake are European protected species.

Licensing

Wales: No licence is needed for the four widespread species, but works must be planned to avoid killing or injury. Sand lizard needs a licence from Natural Resources Wales.

England: No licence is needed for the four widespread species, but works must be planned to avoid killing or injury. Sand lizard and smooth snake need a Natural England licence.

Practical tips

  • Lay survey refugia a week or two before the first check so they can settle.
  • Avoid checks in hot midday sun in July and August, when reptiles are hard to find.

Hazel dormouse

Muscardinus avellanarius

A nocturnal, tree-dwelling mammal of woodland, scrub and species-rich hedgerows. It hibernates in nests on or near the ground from late autumn to spring and is rarely seen, so surveys rely on nest tubes and gnawed hazelnuts.

Key dates, protection and tips

Key dates

  • Nest tube surveysSurvey: mid-Apr to Nov50 tubes in scrub, hedgerow and dense coppice, or 100 in high canopy woodland or poorer habitat, checked monthly for a full season (April or May to November). Adding tubes does not shorten the survey.Source: Bullion et al. (2025); Wells et al. (2025); PTES survey guidance
  • Footprint tunnel surveysSurvey: May to Oct50 tunnels checked and re-inked every two weeks for three consecutive months between May and October, put up two weeks before the survey starts.Source: Bullion et al. (2025); PTES survey guidance
  • Nut searchesSurvey: Sep to DecSearch for hazelnuts opened by dormice after nut fall. Shows presence only.Source: common professional practice
  • HibernationSensitive period: Nov to AprDormice hibernate on or near the ground and may not emerge until April or May. NRW asks for no ground preparation near good habitat from 1 November to 31 March.Source: NRW dormouse good practice guide (2026)
  • Breeding season (dependent young)Sensitive period: Jun to mid-SepNo felling or scrub clearance from 1 June to 31 August, and ideally not in early September.Source: NRW dormouse good practice guide (2026)
  • Above-ground cutting by hand (licensed)Works window: Nov to FebFirst stage of a two-stage clearance. Guidance allows November to March; ending in February avoids the bird nesting season. Stumps and roots stay until dormice are active again.Source: common professional practice
  • Ground clearance (licensed)Works window: May; mid-Sep to OctSecond stage, once dormice are active: May, before females have young, or from mid-September. Check for nesting birds.Source: NRW dormouse good practice guide (2026); common professional practice

Legal protection

European protected species under the Conservation of Habitats and Species Regulations 2017.

Licensing

Wales: Vegetation removal in occupied habitat needs a European protected species licence from Natural Resources Wales.

England: Vegetation removal in occupied habitat needs a Natural England licence.

Practical tips

  • Plan dormouse surveys early. A nest tube survey to show likely absence runs for a full season, so tubes need to be up by April or May.
  • Design mitigation using the Hazel Dormouse Mitigation Handbook (Wells, Chanin and Gubert, 2025).

Plants and habitats

Habitat survey, hedgerows and botany

Habitat surveys map and classify vegetation using UKHab and record its condition. That baseline drives biodiversity net gain in England and the net benefit for biodiversity case in Wales.

Key dates, protection and tips

Key dates

  • Habitat survey and condition assessment (UKHab)Survey: Apr to Sep; Oct (not ideal)April to September is the accepted window for condition assessment. Outside it, condition is scored cautiously and a return visit may be needed.Source: UKHab (2023); common professional practice
  • Hedgerow surveySurvey: Apr to Jul; Aug to Oct (not ideal)Possible April to October, but April and May are best for woodland ground flora.Source: Defra (2007); common professional practice
  • Detailed botanical survey (grassland, wetland)Survey: late Apr (not ideal); May to Jul; Aug to Sep (not ideal)Timed to the flowering of the plant community concerned.Source: common professional practice

Legal protection

Habitats and species of principal importance are listed under section 7 of the Environment (Wales) Act 2016 and section 41 of the NERC Act 2006 in England. Rare plants are protected under Schedule 8 of the Wildlife and Countryside Act 1981. Important hedgerows are protected by the Hedgerows Regulations 1997.

Licensing

Wales: No licence is needed for survey. Removing a countryside hedgerow outside planning permission needs a hedgerow removal notice to the council.

England: No licence is needed for survey. Removing a countryside hedgerow outside planning permission needs a hedgerow removal notice to the council.

Practical tips

  • Book habitat condition surveys in the growing season. A winter visit often means a return visit.
  • Deciding whether a hedgerow is 'important' needs a spring visit to record woodland ground flora.

Invertebrates

Insects, spiders, molluscs and aquatic invertebrates

Invertebrates make up most of the biodiversity on most sites. Specialist surveys target habitats such as brownfield land, deadwood, wetlands and species-rich grassland.

Key dates, protection and tips

Key dates

  • Terrestrial invertebrate surveysSurvey: Apr to SepUsually three to five visits spread from April to September to cover spring, summer and autumn species.Source: Drake et al. (2007); Natural England standing advice
  • Aquatic invertebrate samplingSurvey: Mar to May; Sep to NovSpring (March to May) and autumn (September to November) are the standard river sampling seasons.Source: Environment Agency river sampling method

Legal protection

Some invertebrates are protected under Schedule 5 of the Wildlife and Countryside Act 1981 or the Habitats Regulations, for example marsh fritillary. Many more are species of principal importance.

Licensing

Wales: A licence is needed only for specially protected species.

England: A licence is needed only for specially protected species.

Practical tips

  • Plan several visits across spring, summer and autumn, as different groups peak at different times.
  • Aquatic samples are taken in standard spring and autumn seasons so results can be compared.

Otter and water vole

Otter Lutra lutra, water vole Arvicola amphibius

Otters range widely along rivers, coasts and wetlands and can breed in any month. Water voles live in burrows in steep, well-vegetated banks of slow-flowing water and are active by day.

Key dates, protection and tips

Key dates

  • Otter surveysSurvey: All yearPossible all year. Avoid surveys straight after high flows.Source: Chanin (2003)
  • Water vole surveysSurvey: mid-Apr to SepTwo visits: one between mid-April and the end of June, one between July and September.Source: Dean et al. (2016); Natural England standing advice
  • Water vole breeding seasonSensitive period: Apr to SepAvoid works to occupied banks.Source: Dean et al. (2016)
  • Water vole displacement (licensed)Works window: mid-Feb to mid-AprDisplacement by vegetation removal between 15 February and 15 April, before breeding. Suited to short lengths of bank only (up to 50 m in the handbook), under licence.Source: Dean et al. (2016)

Legal protection

Otter is a European protected species. Water vole is fully protected under Schedule 5 of the Wildlife and Countryside Act 1981.

Licensing

Wales: Works affecting otter resting sites need a licence from Natural Resources Wales, as does water vole displacement or capture.

England: Works affecting otter resting sites need a Natural England licence. Water vole displacement can be done under a Natural England class licence by a registered ecologist.

Practical tips

  • Otters can breed at any time of year, so check for holts and resting sites whenever riverside works are planned.
  • Note river levels on each visit. High flows wash away spraint and latrines and can make an absence result unreliable.

Invasive plants

Japanese knotweed Reynoutria japonica, Himalayan balsam Impatiens glandulifera

Invasive plants found late can stop a construction programme and add cost. Mapping them early means treatment can start in the right season, often a year or more before works.

Key dates, protection and tips

Key dates

  • Japanese knotweed surveySurvey: Apr (not ideal); May to Sep; Oct (not ideal)Dead canes can be found in winter, but the extent is easiest to map in growth.Source: EA and NRW invasive plant guidance
  • Himalayan balsam surveySurvey: Jun to AugEasiest to find in flower.Source: EA and NRW invasive plant guidance
  • Japanese knotweed herbicide treatmentWorks window: Aug to OctGlyphosate works only from late summer into autumn, after flowering. Large stands need two or three years of treatment.Source: NRW knotweed guidance
  • Himalayan balsam pullingWorks window: May to JulPull or cut before seed pods form, usually from July. Repeat visits through the season and for at least two years.Source: common professional practice

Legal protection

It is an offence to plant these species or cause them to grow in the wild (Wildlife and Countryside Act 1981, section 14 and Schedule 9). Soil containing knotweed is controlled waste.

Licensing

Wales: No licence is needed, but on-site burial, movement and disposal must follow Natural Resources Wales guidance and waste law.

England: No licence is needed, but on-site burial, movement and disposal must follow Environment Agency guidance and waste law.

Practical tips

  • Map knotweed in summer and treat it from late summer into autumn, after flowering.
  • Never strim or flail knotweed. Small fragments of stem and root can grow into new plants.

Planning works or a planning application?

Ecoleg programmes and delivers ecological surveys across Wales and England, so the right survey happens in the right season. Call 07356 123706.

Get in touch

How to use this calendar

This is general guidance. The right timing for any site depends on the species present, the habitat, the weather in a given year, the scale of the works and what the planning authority and licensing body require. The windows shown are typical for lowland Wales and England. Upland and northern sites can run later.

Always confirm survey and works timing with a suitably qualified ecologist before committing to a programme.

Updated November 2026.

Main sources

  1. Collins, J. (ed.) (2023) Bat Surveys for Professional Ecologists: Good Practice Guidelines, 4th edn. Bat Conservation Trust.
  2. ILP and BCT (2023) Guidance Note 08/23: Bats and Artificial Lighting at Night.
  3. English Nature (2001) Great Crested Newt Mitigation Guidelines.
  4. Biggs, J. et al. (2014) Analytical and methodological development for improved surveillance of the great crested newt (eDNA). Defra WC1067.
  5. Natural Resources Wales, The use of environmental DNA test for great crested newt licensing purposes (accessed November 2026).
  6. Natural England (2025) Protected species and development: advice for local planning authorities, survey timings table (accessed November 2026).
  7. ARG UK (2010) Advice Note 5: Great Crested Newt Habitat Suitability Index.
  8. Froglife (1999) Reptile Survey: Advice Sheet 10.
  9. Bullion, S., Wolton, R. and White, I. (2025) Hazel Dormouse Conservation Handbook, 3rd edn. Mammal Society.
  10. Wells, D., Chanin, P. and Gubert, L. (2025) Hazel Dormouse Mitigation Handbook. Mammal Society.
  11. People's Trust for Endangered Species, hazel dormouse nest tube and footprint tunnel survey guidance (accessed November 2026).
  12. Harris, S., Cresswell, P. and Jefferies, D. (1989) Surveying Badgers. Mammal Society.
  13. Natural England and Natural Resources Wales badger licensing guidance (current).
  14. Dean, M., Strachan, R., Gow, D. and Andrews, R. (2016) The Water Vole Mitigation Handbook. Mammal Society.
  15. Chanin, P. (2003) Monitoring the Otter. Conserving Natura 2000 Rivers Monitoring Series No. 10.
  16. Bird Survey & Assessment Steering Group (2022) Bird Survey Guidelines for assessing ecological impacts.
  17. Bibby, C.J. et al. (2000) Bird Census Techniques, 2nd edn. Academic Press.
  18. UKHab Ltd (2023) UK Habitat Classification, version 2.0.
  19. Defra (2007) Hedgerow Survey Handbook, 2nd edn.
  20. Ecoleg house standard (2026): nesting season March to August inclusive; nest check within 48 hours before works.
  21. Environment Agency and Natural Resources Wales guidance on managing Japanese knotweed and other invasive non-native plants (current).
  22. Natural Resources Wales (2026) Good Practice Guide: protecting hazel dormice during woodland management and forestry operations, version 1.0.
  23. Environment Agency (2017) Freshwater macro-invertebrate sampling in rivers, operational instruction 018_08.
  24. Drake, C.M., Lott, D.A., Alexander, K.N.A. and Webb, J. (2007) Surveying terrestrial and freshwater invertebrates for conservation evaluation. Natural England Research Report NERR005.
  25. Natural Resources Wales, Japanese knotweed: what you need to know (accessed November 2026).
  26. Bat Conservation Trust guidance on trees, woodland and bats: March to April and September to October are the least vulnerable times (accessed November 2026).
  27. Common professional practice; confirm for each site.