Butterfly transect summary 2016

We reached a significant milestone this year, having completed 10 years of monitoring on both Fleam Dyke and the Roman Road.

Because of poor weather, 2016 got off to a slow start but conditions were much better later in the summer.  For the first time, we covered every week of the season but unfortunately, in week 4, weather conditions were so poor that no butterflies were seen. A total of 24 species were recorded on Fleam Dyke and 23 on the Roman Road.  In terms of total sightings, 2016 was the poorest season since 2012, but numbers were higher than in that particularly bad year.  Compared with 2015, both sites showed a 31% reduction in butterfly numbers.  However, it was not all bad news.  Combining numbers of Small and Essex Skippers, and ignoring the magnitude of changes, 10 species on Fleam Dyke and 7 on the Roman Road showed increased indices relative to 2015.

Sadly, after an excellent season last year, the index for the Chalkhill Blue on Fleam Dyke dropped by 57%, from 2215 to 951, the lowest since 2012.  On the Roman Road, the population of this species is much smaller and the index dropped from 50 in 2015 to just 19 this year.

Our second habitat specialist on Fleam Dyke, the Green Hairstreak, also showed a significant reduction, the index falling from 21 in 2015 to 11 this year but the weather was particularly bad during its flight season.

The Dark Green Fritillary, which appeared on Fleam Dyke for the first time in 2010 with one sighting and showed modest increases to an index of 13 in 2013, has not been recorded in transect counts for the last three years.

On Fleam Dyke, Small/Essex Skippers had a good year, the index equalling the previous record year of 2014.  On the Roman Road, there was a 68% reduction in these species compared with 2015. Similarly, numbers of Large Skipper on Fleam Dyke were very close to those recorded last year but showed a big reduction on the Roman Road.

The Brimstone had a relatively poor season compared with the last 3 years, particularly on the Roman Road where there was more than a 50% reduction compared with last year.  There were mixed fortunes for the whites.  Lower numbers were recorded for Large White, similar numbers for the Small White while the Green-veined White increased on both sites, particularly on Fleam Dyke. The Orange-tip was down in numbers on both sites for the second year in succession.  No Clouded Yellows were recorded this year.

The Common Blue had a very poor year on both sites.  The Brown Argus had another poor season on Fleam Dyke but the index showed an increase from a very low level on the Roman Road.  The Holly Blue had an excellent year, the best since 2013 on Fleam Dyke and on the Roman Road we had by far the highest number recorded in 10 years of monitoring.  No Small Coppers were recorded this year.

It was a mixed year for the vanessids.  Both the Small Tortoiseshell and the Peacock showed a reduction on both sites but numbers were still well above those recorded when these species were at their lowest levels in 2011 and 2012.  The Comma occurs in very low numbers but showed an increase on both sites.  It was an excellent season for the Red Admiral with the highest number we have ever recorded on Fleam Dyke and the best year since 2007 on the Roman Road.  Three Painted Ladies were recorded on the Roman Road and five on Fleam Dyke.  The only year with significant numbers of this migrant species was 2009.

The Ringlet had an average year with a slight increase on Fleam Dyke and a reduction on the Roman Road.  For the Meadow Brown it was the worst year since 2011, with reductions on both sites.  The Gatekeeper indices were also down compared with 2014 and 2015 but were higher than in the previous 4 years. The Speckled Wood had a good year, showing increased numbers relative to 2015.  Although numbers are very small, the Marbled White was again recorded on both sites with indices of 5 and 3 on Fleam Dyke and the Roman Road respectively.  Only one Small Heath was recorded on the Roman Road this year and on Fleam Dyke there was almost a 50% reduction compared with 2015, with an index of 21.

Chalkhill Blue on Fleam Dyke

Chalkhill Blue on Fleam Dyke