UKBMS Transects

Are you thinking about becoming a Transect walker?

Below is a series of questions from someone who might be interested in contributing and curious to find out more and what is involved in this most rewarding role.

Did you know on a good summer day up to 60 or more Yorkshire volunteers can be doing transect walks? Transect recorders form a small army of rarely mentioned conservation heroes working between them about 3000 hours a year in Yorkshire. A sole recorder on one transect who walking every available week (see later) might over a year spend time equivalent to a full working week.

Why do we record?

Butterflies are the most recorded taxonomic group globally and particularly in the UK. They are also some of the most sensitive species to changes in our climate and their natural environment and typically undergo large year-year variations and movements as a result. Butterflies (and moths) occupy key positions in ecological communities because their larvae are mostly herbivorous and in turn they are food for other organisms especially birds, provide hosts for invertebrate parasites and act as pollinators. The large dataset we help produce allows scientists internationally, who regard our data as of the highest quality, to pick out the effects on abundance and species richness across the UK because of the fine-grained geographic coverage over nearly 40 years of recording.

The United Kingdom Butterfly Monitoring Scheme (UKBMS) is regarded as the most credible ‘canary in the cage’ of the health of our environment. This subject is now at the heart of topical debate with governments declaring we are now in a biodiversity as well as climate emergency. Each generation ‘resets’ to a much lower ‘norm’ and only the oldest of us now remember the moth snowstorms in our car headlights or our insect-splattered windshields of summers gone. Our data therefore has an important role to play, and even more so in the future

Where does our data actually come from?

Yorkshire produces about 50,000 records excluding the Big Butterfly Count BBC of about 25000. Data is gathered through its network of county recorders who verify and compile records from a variety of sources. Typically a county’s transects would be one-half to two-thirds of total records. Then 10% each from website, casual records, BBC, and irecord with 5% from the Wider Countryside Butterfly recording Scheme (WCBS) and a few percent from the Garden Butterfly Scheme. In Yorkshire about 30% come from our transects and a disproportionate one-third from BBC and the rest from iRecord and casual records. This does prompt some questions about how representative our data is? Does BBC skew the whole, not only because it might inflate common species but is sensitive to earliness versus lateness of seasons in different years. Does a heavy reliance on casual recording mean it is more a record of the recorder activity skewing the data by seeking out our rare species or are these two approaches actually helping in restoring a balance? Each is for different purposes and together they provide a better overview of the county’s butterflies than either would alone. Casual recording is better at picking out species movement while transects recording is superior at measuring changes longer term but does require much more organising and volunteer effort in forming the majority of a counties records

Where does the data go?

Our records provide the essential foundation for conservation work to help the UK’s declining butterflies. Records show how butterflies are faring so conservation efforts can be targeted at those most at risk of extinction. They can help reveal the impact of climate change and other environmental issues on our butterfly populations. They underpin the management of important butterfly sites, help protect habitats through the planning system and enable Butterfly Conservation to produce regular State of the UK’s Butterflies reports, local and national atlases and Red Lists of priority species.

Why walk transects?

Transect data has much more scientific validity than casual recording, as the results are more comparable year on year because of the rules under which they are undertaken, which attempt to iron out changes in numbers due to different people recording in different ways. It also takes account of changing weather conditions during a walk. Casual recording or targeted surveys win hands down every time if you want to detect and track rapidly expanding species, However, they are very poor ways to detect declines which the transect methodology tends to pick up better Transects actually started in Yorkshire with Deepdale and Peter Robinson doing the very first in the UK. Some of our transects date back to1970 although I've only looked at the current UKBMS which dates back to 1995. This heritage means some routes have 20 plus years of uninterrupted recording which greatly adds to their value.

What's involved in doing a transect?

The Pollard walk is accepted scientifically as producing the most comparable valid indicators. A fixed route is walked each week from 1st April till end of September, 26 weeks in all, providing suitable weather conditions are met during the middle hours of the day 10:45-15:45. Counting takes place within a 5m by 5m cube immediately in front of the walker. On occasion recorders walk when the minimum weather conditions are not met. In fact, one of the main issues for recorders is with finding a weather slot. You may walk at 13’C providing it is sunny, and walks are not undertaken if overcast unless temperature is above 17’C. Each transect has 5-15 sections reflecting changes in habitat. Most are around 2km and take about an hour to walk. Sunshine is recorded as a percent of time a shadow is cast on the ground for each section. These same rules apply to WCBS and single-species transects.

Would you like to know more?

Take a look at our video which covers identification skills as well as the transect walking technique called the Pollard walk HERE or watch here:

Find the official guide HERE . How to input data HERE and the Recording Form HERE

To start your journey go to UKBMS .

There is an annual get together of all recorders get a chance to talk about their transects and share experience see HERE

If you want to know more about where our transects are and where we are short see below.

Where do we walk?

Many of our scarcer species are habitat specialists and are only found in certain woodlands or unimproved grasslands, often on nature reserves, and a transect provides a proven method of monitoring the health of these populations. More than half of the Yorkshire transect sites are managed by YWT plus others from RSPB, LNR’s, NNR’s and NT. These organisations are instrumental in most of our transects because they want to know how well they are managing their sites. It is often their own volunteers whom we have helped train who carry out the surveys. Transects are also adopted by biodiversity sites but there are many transects in Green spaces and the wider countryside even verges.


Coverage is displayed in a interactive map below with active transects ticked in green; those not monitored since 2020 in orange and 2019 or older in red.

Is there more than one type of Transect?

There are different types of transects for different purposes. All follow a defined route and all species are counted through the flight season on our traditional transects. However there are species like Pearl Bordered Fritillary, Northern Brown Argus and Large Heath in a particular habitat which often has little interest outside of its flight period. So to save volunteer effort in often quite difficult terrain single species transects are undertaken, usually weekly, for just the flight season. The third type of transect is the timed count where only a single species is counted for a specified time. These are useful in monitoring some of our more tricky tree canopy species such as Purple or White-letter Hairstreaks which are best recorded by spending 5-10 minutes observing. Short timed counts beneath suitable trees or in glades on woodland transects would be a useful ‘bolt on’ during these species flight seasons greatly adding value.

How many do we walk?

There are 90 transects across Yorkshire registered on the current version of UKBMS shown below.

Nearly 70 had more than a single walk in 2021. In 2020, during the pandemic 55 transects were walked, while in 2019 62.

Transect web copy

Where are the priorities?

The map below shows areas of Yorkshire where we really need more transects. They include the North York Moors and Clevelands Hills, the Wolds , the Magnesian limestone ridge, the Aire, Wharfe and Nidd Valleys , the coal measures and the Dark Peak. The priority areas contain suggestions for sites. have a look and see if there is one near you or maybe you know somewhere interesting close by where you live which is within one of the priority area shown. In which case do please be in contact our transect co-ordinator

NB Volunteers are always needed on the Yorkshire Dales National Park