I have been trying to make sense of this year's drought in the UK. Can we use the numbers of records? For this exercise I looked at the numbers of hoverfly records extracted from social media per week in the preceding 5 years and produced two graphs. One compares the years (Figure 1) and the other compares 2018 against the average for the preceding 5 years (Figure 2). It is clear from Figure 1 that each year is so different that it is almost impossible to make any comparison. It should be noted that the numbers of records in 2013 and 2014 were small in comparison with 2016, and that the numbers of records in late summer and Autumn 2016 were much greater than in any of the other 4 years. 2016 was the peak year for data extraction direct from the UK Hoverflies Facebook page, since when many of the most active recorders of the time have switched to maintaining their own spreadsheets. In addition, the autumn of 2016 was unusually warm and saw recording extend far longer than normal (into early November).
|Figure 1. Numbers of hoverfly records extracted from social media between 2013 and 2018|
There is more to be made of Figure 2 in so far as it is clear that the general trend is similar with peak numbers occurring in August. A clear drop in the numbers of records during the drought is also apparent, as is the approximate 2-week difference in the start of the season as a result of the length of the last winter. Nevertheless, the range in numbers of records between 2013 and 2017 is substantially skewed by the first year when the UK Hoverflies Facebook group was launched (mid summer 2013). In that year, there was relatively little activity if one bears in mind the levels of activity in 2016.
|Figure 2. Numbers of hoverfly records extracted from social media in 2018 against an average for the previous 5 years (2013 to 2017)|
|Figure 3. Numbers of species recorded from social media in the years 2013 to 2018. Note that whilst the totals for 2013 and 2014 are lower than those for later years, the disparity is not as great as in the numbers of records (Figure 1). |