Which dates matter?
What can be done with the data?
The data largely show this. Hitherto, hoverflies have been the preserve of a relatively small body of recorders. For forty years, about 20 people supplied 50% of the data assembled by the Hoverfly Recording Sscheme (HRS), very few of whom would have made much effort until the spring had fully arrived. The dynamics have changed, and although we still have a nucleus of about 25-30 highly productive specialist recorders (above 500 records a year), we have many more whose combined efforts are really helping to develop a valuable picture (several of whom now contribute many hundreds, or in one case thousands, of records). The new recruits start from a very different perspective and want to get out.To illustrate this, I offer two brief analyses relating to patterns of spring emergence.
Composition of the early spring faunaIf one starts with the question 'how does spring 2016 compare with previous years?' We can break the data into the numbers of records of individual species, but this does not take account of variations in the numbers of recorders. So, presenting data as a proportion of all records received for a given timescale is one option.
|Figure 1. Records of hoverfly species in March 2014 to 2016 presented as the proportion of all photographic records covering the period 01-25 March.|
What is very clear is that the composition of the fauna in different years can vary considerably amongst the more abundant species. As might be expected about a quarter of the total species list makes up the bulk of the records, but within this there are two obvious trends. In 2014 and 2016, Eristalis pertinax is far more prevalent in the data than in 2015. There is an obvious reason when you look at the composition of 2015 data: In 2015, Episyrphus balteatus, Eristalis tenax and Meliscaeva auricollis make up far more of the dataset. These three species are typical of winter months and E. balteatus and E. tenax predominantly over-winter. Thus it seems that 2015 was a later year than either 2014 or 2016 where Eristalis pertinax was much more abundant. E. pertinax, in contrast does not generally over-winter and thus the dominance of this species in the dataset tends to suggest that spring has arrived a little earlier.
And at species level?
|Figure 2. Phenology of Epistrophe eligans in 2014 based on photographic records.|
|Figure 3. Phenology of Epistrophe eligans in 2015 based on photographic records.|
And the moral of the story?
And, for that splendid band of photographic recorders? I hope these brief examples show just how important your contributions are. This level of activity starts to elevate the hoverflies from the margins to the mainstream of insect recording.