Butterfly Transect

I find co-ordinating the local butterfly records really interesting. I hear first-hand about rare species that have been spotted and occasionally about something new. However, because more people are sending in records each year, I wonder if I am getting a false impression about how well the butterflies are doing here.
The UK Butterfly Monitoring Scheme operates a system of butterfly transects, which give a much better picture of how the local butterflies are doing. Each week between April and September I walk a set route near where I work and I count the number of butterflies I see within an area five metres in front of me and two and a half metres to either side.
I started my transect four years ago after noticing how many butterflies there were in a meadow where I often walk during my lunch break. I was a little disappointed when half way through the year the weather took a turn for the worse and the number of butterflies reduced accordingly. The following year it was even worse!
Last week I plotted the results of the last four years transects onto graphs and I noticed an interesting correlation between the number of butterflies and the weather at the time.
On the graphs below, week 1 is the first week in April and week 26 is the last week in September. Normally butterflies will start flying in April and peak about in the middle of May, there is a quiet period in June and then the summer species come out peaking again about the end of July.

In 2011 we had a great spring, but a horrible cold, wet summer. You can see that the butterfly numbers picked up well, but then dropped off when the bad weather hit. I counted a total of 506 butterflies that year.

2012 was the worst year I can remember. It seemed to rain almost every day! I was surprised to see any butterflies on the few occasions when the sun came out. However, you can see that the number of butterflies was considerably down on normal. I only 361 butterflies on my transect that year.

In contrast 2013 was one of the best years I can remember. It is interesting to see that the spring populations were low as a result of the bad weather their parents had experienced in 2012. I still managed to count 523 butterflies on my transect, though.

This year the weather was great again, although it did cool down quite a bit in August and September. The graph above shows what I would consider to be close to a normal number of butterflies. I counted a total of 1175 butterflies on my transect this year. So this really confirms that 2014 has been a fantastic year for butterflies here.