Recording +



The branch magazine Argus is published regularly and details of both it and our other publications can be found on the publications page

What is the difference between formal recording UKBMS and Butterflies of the New Millenium (casual) recording? How do they work together?

This is a crucial thing to understand. Formal recording, or monitoring like UKBMS and WCBS allows an assessment of butterfly abundance by using a quite stringent set of rules often referred to as the Pollard Walk methodology. This allows scientific valid comparisons to be made . This data is highly priced as it allows trends to be analysed. It allows us to see what is happening to a species, its responses to climate change, or, to changes in its habitat. Casual records like those from your garden or 'out and about' go into the BNM (Butterflies for the New Millennium) which allows fine grained distribution mapping to be made and a 'clue' to abundance at individual sites. The branch works closely with the Yorkshire Naturalists' Union and promotes the jointly administered but independent recording scheme known as ButterflyNet Yorkshire, with a co-ordinator in each of Yorkshire's five vice counties and species co-ordinators for the county as a whole. It allows us to see if species are expanding or contracting and location of hotspots but it cannot be used to do any valid assessment of abundance as the data is not gathered in a systematic way.

So each, formal and casual 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 order to form the majority of records which most counties aspire too.

So how does Yorkshire measure up?

Yorkshire produces about 75,000 records per annum. Typically a county’s transects would be 50-70% of total records. In Yorkshire about 25% come from UKBMS, and less than 5% from the Wider Countryside Butterfly monitoring Scheme (WCBS) and Garden Butterfly Scheme. There is a somewhat disproportionate 33% from the Big Butterfly Count (BBC) and the rest are casual records with about 10% each from irecord, the website, and other means

This does prompt questions about how representative our data is? Does BBC by shear number skew the whole, not only because it might inflate common species but is sensitive to earliness versus lateness of seasons in different years as it is only taken over a fixed 3 week period. Is it sufficient to just monitor butterflies on nature reserves, where they can prosper, as in UKBMS so how representative are they? 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 only visiting popular sites? Although Yorkshire is out of balance the different approaches actually do helping in keeping some balance. However Although we might know fairly well the distribution of our species and a accurate knowledge of species trends we don't really know what is happening in the wider countryside outside of reserves and hotspots. The answer was to introduce the the wider countryside butterfly monitoring scheme that uses randomly chosen 1km squares throughout the UK. They require just two visits a year using the same systematic methodology as UKBMS thus allowing a meaningful assessment to be made from a small amount of data . Unfortunately the scheme has not had much take up in Yorkshire with just 5 of its allocated squares being visited in 2020

UK Butterfly Monitoring Scheme (UKBMS)

Transect Walkers

Transect Walkers help to monitor all the butterflies in selected sites throughout the summer. This provides information on changes in the abundance and status of butterflies throughout the UK and also helps guide the management of many nature reserves, not only our own but those of the National Trust, the Wildlife Trusts, the Woodland Trust, RSPB and others.

Butterflies are recorded along a fixed route (a transect) on a weekly basis from the beginning of April until the end of September. Transects are typically about 2 to 4 km long, taking between 45 minutes and two hours to walk. They have to be visited between 10.45am and 3.45pm and only when weather conditions are suitable for butterfly activity.

Due to the vagaries of the weather, it is rare in practice to achieve a full set of 26 weekly counts even if you have no other commitments and can visit the transect at any time in the week It is best to take on a transect as part of a team of several people. In fact, it may best to begin by helping an existing team, so as to learn the methods and develop the field skills required.

The UK Butterfly Monitoring Scheme is organised and funded by Butterfly Conservation (BC), the UK Centre for Ecology and Hydrology (CEH), the British Trust for Ornithology (BTO), and the Joint Nature Conservation Committee (JNCC)

Our Branch Transect Coordinator Nick Hall can be contacted by email if you have any questions or are interested in walking a Transect.

Transect recording forms and resources are available from the UKBMS website.

December 2020: Many thanks to all the branch Transect Walkers that monitored sixty sites across Yorkshire in 2020

Single species transect surveys

Single species transect surveys are especially useful on nature reserves with one or more uncommon species that are the direct object of management.

The transect must follow the standard method and be carried out at least once a week throughout the flight period and more frequently if possible. The focus on a single species of course reduces both the time required to walk the transect and, more significantly, the number of weekly counts that are needed.

Timed Count Monitoring

Unlike transects, timed counts need only be carried out once a year at a site to provide meaningful results which makes then a useful ‘reduced effort’ method for monitoring rare butterflies, especially those whose distributions change over time across large sites.

The count must be done as near as possible to the peak flight period of the species in question. As with transect walking, timed counts should ideally be made between 10:45 and 15:45 and suitable weather is essential.

First, quickly walk the site to identify the extent of the adult flight area. If adults are patchily spread over a large area, it is better to identify sub-populations and survey them separately. Then count adults by walking the site, either in a series of parallel lines or in a zigzag path, covering the flight area as thoroughly and evenly as possible. This usually takes between 5 and 60 minutes depending on the size of the colony area. It is important the walk passes through areas of high and low adult density: If only the best patches are visited, analysis may over-estimate abundance.

Please contact Nick, our Branch Transect Coordinator if you have any questions about Transects or other surveys mentioned on this page

Please ensure your data is submitted to the UKBMS by October 31st each year to allow your local co-ordinator time to verify records and ensure their inclusion in national/regional analyses. Please enter transect data online at