Report on 2021 Butterfly Transect Season (1st April to 30th Sept)

Apart from the availability of members of the team, the week’s weather forecast is the next most important factor when choosing the day for the weekly transect – butterflies do not like the cold or wet. Even though the frequently poor weather of the spring caused us to miss three transect weeks, we found 23 sufficiently warm and/or dry days over the rest of the season’s 26 possible weeks for our transects (although one was abandoned half way round because of the onset of a heavy downpour).
Despite generally getting it right weather-wise, we were aware quite early in the season that our butterfly counts were on the low side this year, and it didn’t seem that the weather was entirely to blame. We were not alone in this finding: Bill Downey of BCT reported that butterfly numbers reported across the region had dropped this year.
To illustrate the situation: below are the average numbers of butterflies from our individual transects over each of the following years:

2021’s figure reflects a low count across many of the species we have recorded on our site since we started our transects in 2016. The major ‘losers’ on our patch were the Meadow Browns, Marbled Whites, Gatekeepers, Small Heaths, Common Blues and Chalkhill Blues, all of which we rely on to provide the large numbers to boost our annual totals. Even our flourishing area of Kidney Vetch on Hither Field only produced two Small Blues for us to record. There were, however, a few ‘gainers’: these were the Peacocks, Purple Hairstreaks and Clouded Yellows, which recorded higher counts than usual, although these are species seen in relatively small numbers that do not have a significant bearing on our annual tallies. 
Here is a spreadsheet showing the count details for each transect for this and previous years.
​Report by Brian Gardner

A beautiful day on the final transect of 2021, crossing the recently mown Hither Field. Spot the team!