If you're planning a development, the single biggest cause of delay is missing the survey window for a protected species.
Bat emergence surveys can only be done May to September. GCN eDNA has a window of mid-April to late June. Dormouse nest tube surveys need to run April through November. Miss the window and you're waiting until next year - potentially adding 12 months to your project timeline.
This guide covers the optimal and sub-optimal survey periods for every commonly surveyed protected species in the UK, so you can plan ahead and avoid costly delays.
Why Survey Timing Matters
Protected species surveys in the UK are seasonally constrained because the animals themselves are seasonal. Bats hibernate November to March. Great crested newts breed in spring. Reptiles bask in April and September but hide during peak summer heat.
Local planning authorities will not accept survey data collected outside the recommended survey period. If you submit a bat emergence survey done in March, it will be rejected. Your ecologist will tell you this - but by then you may have already lost the season.
The key principle: plan your ecology surveys before you need them, not after.
Preliminary Ecological Appraisal (PEA)
A PEA - also known as an Extended Phase 1 Habitat Survey - is the starting point for almost every ecological assessment. The good news is that the desk study component can be done at any time of year. The walkover survey is best done April to September when vegetation is identifiable, but can be undertaken year-round.
Optimal period: April - September
Sub-optimal: October - March (reduced ability to identify plant species and assess habitats)
Survey effort: 1 site visit for the walkover, plus a desk study
A PEA should always be done first, because it determines which Phase 2 species surveys are needed. Getting your PEA done in autumn or winter means you can schedule any required species surveys for the start of the following season - no time wasted.
Pro tip: Use EcoCheck to run the desk study component instantly. Enter your grid reference and get every SSSI, SAC, SPA, Ancient Woodland, Priority Habitat, GCN Risk Zone, and protected species record within your chosen buffer in seconds.
Bat Surveys
Bats are the most commonly encountered protected species on development sites and have some of the strictest survey timing requirements.
Preliminary Roost Assessment (PRA)
An internal and external inspection of buildings or trees to assess their potential to support roosting bats.
Can be done: Year-round
Best practice: Schedule early enough to allow Phase 2 surveys if needed. If a PRA in October identifies moderate bat roost potential, you'll need emergence surveys the following May-August.
Survey effort: 1 visit
Emergence and Re-entry Surveys
Dusk emergence and dawn re-entry surveys to determine whether bats are using a building or tree as a roost.
Optimal period: May - August
Sub-optimal: April (early season, lower activity) and September (late season)
Not possible: October - March (hibernation period)
Survey effort: 1-3 visits depending on roost potential. Low potential buildings need 1 survey. Moderate potential need 2 surveys (at least 1 dusk and 1 dawn). High potential or confirmed roosts need 3 surveys (at least 2 before end of August). Surveys must be at least 2 weeks apart.
BCT Guidelines: All bat surveys must follow the Bat Conservation Trust Good Practice Guidelines (4th edition, 2023).
Bat Activity Surveys
Transect surveys to assess bat foraging and commuting activity across a site. Typically required for larger sites.
Optimal period: April - October
Survey effort: Monthly visits throughout the active season (typically 3-7+ visits depending on site size)
Hibernation Surveys
Required where underground sites (mines, tunnels, cellars, ice houses) may support hibernating bats.
Optimal period: December - February
Survey effort: 1-2 visits during the hibernation period
Great Crested Newt (GCN) Surveys
Habitat Suitability Index (HSI)
An assessment of pond suitability for GCN based on 10 habitat criteria.
Can be done: Year-round (though some criteria like shade and macrophyte cover are best assessed April-September)
Survey effort: 1 visit per pond
GCN Presence/Absence Surveys (Traditional)
Torch surveys, bottle trapping, egg searching, and netting.
Optimal period: Mid-March to mid-June
Peak period: Mid-April to mid-May (at least half of survey visits must fall within this window)
Survey effort: 4-6 visits, with at least 2 visits during the peak period
eDNA Surveys
A water sample collected from a pond and sent for laboratory analysis to detect GCN DNA.
Survey window: 15 April - 30 June
Survey effort: 1 visit per pond (but timing is critical - samples taken outside the window are invalid)
Note: eDNA determines presence or absence only. If GCN are detected, further population class surveys may be required.
GCN District Level Licensing
In areas covered by Natural England's District Level Licensing scheme, traditional GCN surveys may not be required. Instead, the GCN Risk Zone map determines the approach. Check whether your site is in a Red, Amber, or Green zone using EcoCheck or Natural England's open data geoportal.
Reptile Surveys
Surveys for common reptile species (slow worm, common lizard, grass snake, adder) and rarer species (sand lizard, smooth snake).
Optimal period: April - May and September (when reptiles are basking most actively)
Sub-optimal: June - August (high temperatures mean less basking activity and lower detection rates)
Not possible: November - February (hibernation)
Survey effort: 7 visits for presence/absence. 20+ visits for population estimates. Artificial refugia (corrugated tin or roofing felt) should be deployed at least 2 weeks before surveys begin.
Dormouse Surveys
Nest Tube Surveys
Dormouse nest tubes are deployed on site and checked monthly.
Survey period: April - November
Optimal detection: August - November (when dormice are most likely to use tubes)
Survey effort: Monthly checks (minimum 5 visits). Tubes should be in place by April for best results. The longer tubes are deployed, the higher the chance of detection.
Nut Search
A search for characteristically gnawed hazel nuts.
Survey period: September - December (after nuts have fallen but before leaf litter covers them)
Survey effort: 1 visit
Water Vole Surveys
Optimal period: Mid-April to September
Best months: April-May (spring) and August-September (late summer), when signs are most visible
Sub-optimal: October - March (reduced activity, harder to detect)
Survey effort: 2 visits, ideally one in spring and one in late summer
Key signs: Latrines, burrows, feeding stations (characteristically angled-cut vegetation), footprints, and runways through bankside vegetation.
Otter Surveys
Can be done: Year-round
Best period: Spring (when bankside vegetation is low, improving visibility of spraints, holts, and slides)
Survey effort: Variable depending on watercourse length. Surveys involve searching for spraints, footprints, holts, couches, and slides along watercourses.
Badger Surveys
Can be done: Year-round
Best period: February - April (when setts are most active and vegetation is low) and October - November
Survey effort: 1-2 visits for sett surveys. Bait marking to determine territory boundaries requires extended monitoring (4+ weeks).
Breeding Bird Surveys
Survey period: March - August (varies by species)
Optimal period: April - June for most species. Some early nesters (e.g. raven, crossbill) start in February.
Survey effort: 3-4 dawn visits for a standard breeding bird survey. Wader surveys may require additional visits.
Wintering Bird Surveys
Survey period: October - March
Survey effort: Monthly visits (typically 3-6 visits across the winter period). Required for sites near estuaries, coasts, wetlands, and other areas supporting overwintering bird populations.
White-clawed Crayfish Surveys
Optimal period: July - October (when water temperatures are above 8 degrees C and crayfish are most active)
Not possible: December - March (water temperatures too low)
Survey effort: 1-3 visits using hand-searching, torch surveys, and/or trapping. eDNA is increasingly used as a screening tool.
Note: Surveyors need a specific licence to handle white-clawed crayfish.
Barn Owl Surveys
Optimal period: March - August (breeding season)
Can also be done: Year-round for building inspections and pellet analysis
Survey effort: 1-3 visits depending on site context
Planning Your Survey Programme
The golden rule is to commission your PEA as early as possible. A PEA done in winter gives you the full spring and summer to complete any required Phase 2 surveys. A PEA done in July might mean waiting until the following April for bat surveys.
Here's a practical timeline:
October - February: Commission PEA (desk study + walkover). Identify which Phase 2 surveys are needed. Book your ecologist for the coming season.
March - April: Badger surveys, early breeding bird surveys, HSI assessments for GCN ponds, reptile refugia deployment.
April - June: GCN surveys (traditional and eDNA), bat emergence surveys begin, dormouse tube deployment, water vole surveys, reptile surveys.
May - August: Peak bat survey season, breeding bird surveys, dormouse tube checks, invertebrate surveys.
September - November: Late reptile surveys, dormouse nut searches, badger surveys, wintering bird surveys begin.
December - February: Bat hibernation surveys, wintering bird surveys, desk study preparation for next season.
Start With the Desktop Study
Every survey programme begins with understanding what's already recorded at your site. Before commissioning any Phase 2 surveys, run a desktop study to identify which designated sites are nearby, which species have been recorded, and what the GCN risk zone classification is.
EcoCheck lets you do this instantly for any GB location - enter a grid reference, postcode, or coordinates and get the full constraints picture in seconds. Use it to scope your survey programme efficiently and avoid expensive surprises later.
Patrick O'Connor is a Freelance Ecologist at Kinterra Consulting and the developer of EcoCheck - an instant ecological desktop assessment tool for any GB location. Try it free for 3 days at ecocheck.co.