Ecological survey work is governed by seasons more than by capacity. Species are surveyable when they are active, and outside those windows a survey either cannot be done or cannot be relied on. Planning around that is most of the discipline.
The windows, survey by survey
The periods below are the ones generally recognised in UK survey guidance. They are indicative: optimal windows are narrower than possible ones, weather matters as much as the calendar, and the right answer for a particular site always depends on the site.
| Survey | J | F | M | A | M | J | J | A | S | O | N | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Preliminary Ecological AppraisalYear-round. Botanical detail strongest Apr–Sep. | January: yes | February: yes | March: yes | April: yes | May: yes | June: yes | July: yes | August: yes | September: yes | October: yes | November: yes | December: yes |
| Preliminary Roost Assessment (bats)Year-round. | January: yes | February: yes | March: yes | April: yes | May: yes | June: yes | July: yes | August: yes | September: yes | October: yes | November: yes | December: yes |
| Bat emergence / re-entryOptimal May–Aug. Suitable weather required. | January: no | February: no | March: no | April: no | May: yes | June: yes | July: yes | August: yes | September: yes | October: no | November: no | December: no |
| Bat activity transectsApr–Oct, weighted to the summer months. | January: no | February: no | March: no | April: yes | May: yes | June: yes | July: yes | August: yes | September: yes | October: yes | November: no | December: no |
| Great crested newt — eDNAMid-Apr to end Jun only. | January: no | February: no | March: no | April: yes | May: yes | June: yes | July: no | August: no | September: no | October: no | November: no | December: no |
| Great crested newt — presenceMid-Mar to mid-Jun, half of visits by mid-May. | January: no | February: no | March: yes | April: yes | May: yes | June: yes | July: no | August: no | September: no | October: no | November: no | December: no |
| ReptilesApr–Jun and Sep. Avoid the hottest weeks. | January: no | February: no | March: no | April: yes | May: yes | June: yes | July: yes | August: yes | September: yes | October: no | November: no | December: no |
| DormiceApr–Nov, with effort weighted to Sep–Oct. | January: no | February: no | March: no | April: yes | May: yes | June: yes | July: yes | August: yes | September: yes | October: yes | November: yes | December: no |
| Breeding birdsMar–Jul, early morning visits. | January: no | February: no | March: yes | April: yes | May: yes | June: yes | July: yes | August: no | September: no | October: no | November: no | December: no |
| Wintering birdsOct–Mar. | January: yes | February: yes | March: yes | April: no | May: no | June: no | July: no | August: no | September: no | October: yes | November: yes | December: yes |
| Botanical / UKHab conditionApr–Sep. Grassland is hard to assess in winter. | January: no | February: no | March: no | April: yes | May: yes | June: yes | July: yes | August: yes | September: yes | October: no | November: no | December: no |
| Badger sett surveyYear-round; easiest when vegetation has died back. | January: yes | February: yes | March: yes | April: yes | May: yes | June: yes | July: yes | August: yes | September: yes | October: yes | November: yes | December: yes |
| Otter and water voleApr–Sep for water vole; otter year-round. | January: no | February: no | March: no | April: yes | May: yes | June: yes | July: yes | August: yes | September: yes | October: no | November: no | December: no |
Indicative periods based on standard UK survey guidance. Not site-specific advice — for a particular site, ask.
Where a survey sits at the very edge of its window, it is usually better to say so and plan for the following season than to produce a report with caveats a planning officer will pick up.
Planning around it
Three habits make the difference on most projects:
- Get the appraisal done before the design is fixed, not after the application is validated
- Treat survey seasons as fixed points in the programme, like a planning determination period
- Where a window is about to close, say so early — a fortnight of notice is often the difference between this season and next
If a window has been missed
It is not always fatal. Depending on the species and the proposal, there may be options: a precautionary approach, a revised scope, or works phased around the constraint. It is worth a conversation before assuming a year has been lost.
General guidance only. Ecological requirements depend on the site, the proposal and the local planning authority — for advice on a specific project, get in touch.
