Marsh fritillary, dormice and the survey calendar

A protected species survey calendar is the single most useful page in an ecology brief, and most schemes are programmed without one. Great crested newt environmental DNA sampling runs from the middle of April to the end of June. Marsh fritillary larval webs are counted in late summer. Dormouse nut searches want the autumn and winter. Wintering bird surveys run October to March and breeding bird surveys run March to August, so those two alone occupy the whole year.

Miss a window and the answer is not a shorter survey. It is next year.

Why the windows differ so much

Each method depends on the animal doing something detectable, and animals do different things at different times.

Bats have to be flying out of a roost to be counted leaving it, so emergence surveys need warm evenings in the active season. Newts have to be in the pond for their DNA to be in the water. Dormice have to be building nests for nest tubes to record them, and have to have eaten hazelnuts for a nut search to find the characteristic opening. Marsh fritillary larvae spin conspicuous webs on devil's-bit scabious in late summer, which is far easier to find than a single adult butterfly in a brief flight period.

The survey window is therefore a biological fact, not a convention that a fee or a deadline can move. This is the part clients find hardest to accept, and it is worth saying plainly at the first meeting.

The calendar

Treat these as the generally accepted periods used in England. The optimal period inside each window is usually narrower, and the local ecologist's judgement on a specific site governs.

The habitat survey row matters more than it used to. The biodiversity baseline is taken from habitat condition assessed in the field, and a baseline recorded in February is not defensible, so the Biodiversity Net Gain Assessment is now tied to the botanical season as firmly as any species survey.

Windows that barely overlap

Three combinations cause most of the programme pain.

Wintering birds and breeding birds between them cover the calendar. A site needing both has a 12 month ecology programme before anything else is considered.

Dormouse nut searches and nest tube surveys sit on opposite sides of the year, and a nest tube survey is not a single visit. The recognised approach scores monthly visits across the season, with different months weighted differently, so a tube survey started in August cannot reach the required score before the tubes come down in November.

Marsh fritillary larval webs and great crested newt sampling are three months apart, which means a site with both has to be visited in spring and again in late summer, with the design frozen in between or redone after.

The risk of committing to one season

Clients ask whether a single season will do. Sometimes it will. Often the honest answer is that a single season gives you a result for that season, and if conditions were poor, if the weather closed the window, or if the result is equivocal, you have no fallback.

Two specific risks are worth naming. A negative result from a sub-optimal visit is weak evidence, and a case officer or an objector will say so. And a result that triggers further work, such as a presence survey following a positive water sample, has to happen inside the same season or it slips a year.

Build contingency visits into the brief rather than bolting them on later. The marginal cost of a planned extra visit is a fraction of the cost of a missed year.

Where a desk study narrows the list

The Preliminary Ecological Appraisal exists to stop you surveying for things that cannot be there. A record search from the local environmental records centre, the statutory designations, aerial imagery, habitat suitability on and adjacent to the site, and a walkover will usually remove half the candidate species list.

Marsh fritillary is a good example. It needs damp grassland with devil's-bit scabious and it has a restricted distribution, so on most development sites the appraisal rules it out in a paragraph. Dormice need connected woodland or hedgerow and are absent from large parts of England. Crayfish need the right watercourse.

What the appraisal cannot do is rule things in from the desk. It tells you what to survey and when, which is exactly what the calendar needs.

Any survey or licence work for European protected species requires a suitably licensed ecologist under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017. A drafted Protected Species Survey document can carry the reporting structure, and the fieldwork, the judgement and the licence application stay with that ecologist. Survey effort for bats is the most commonly disputed element, and our note on bat emergence survey effort and roost suitability explains how it is set.

Programme consequences for a land purchase

On an option or a conditional contract, the ecology calendar often sets the longstop date, and nobody notices until the survey report lands.

Three practical moves:

1. Commission the preliminary appraisal before exchange, not after, so the species list and the seasons are known when the dates are negotiated.
2. Write the survey programme into the conditional contract, with the longstop set after the last available window plus a margin.
3. Protect the baseline. Clearance, grazing changes or mowing between exchange and survey can alter the habitat and the biodiversity baseline, and a vendor tidying up a site has cost buyers real money. Vegetation clearance also carries its own timing duty, which we cover in nesting bird checks before vegetation clearance.

Recording the calendar for the client

Produce it as a one page Gantt chart with the months across the top, one row per survey, the optimal period shown darker, and the decision points marked: appraisal complete, species list fixed, baseline recorded, licence applied for, clearance window open.

Add two columns that get missed. Who holds the licence for each piece of work. And what happens if the result is positive, because the follow-on survey has its own window.

An illustrative case: a 4 hectare former smallholding with ponds, hedgerows and rough grassland, bought with a 12 month option. The appraisal in November identified newts, reptiles, nesting birds, bats in two outbuildings and a dormouse possibility in the boundary hedge. The surveys ran from March to October, the metric baseline was recorded in June, and the application went in the following January. Fourteen months from option to submission, none of it recoverable, and all of it foreseeable from the first site visit.

Enter your postcode on PlanScope to see which ecology reports a site is likely to need before you fix the programme.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.