Saturday, 16 September 2017

Autumn field meeting - Tarbet - some reflections

For more than 40 years there have been Autumnal field meetings organised, primarily, to survey the cranefly and fungus gnat faunas of the British Isles. Initially they were run by Alan Stubbs in his role as Head of Entomology at the Nature Conservancy Council. Upon Alan's retirement in 1991 there was no capacity to organise these meetings and they became a voluntary effort. Peter Chandler ran them for many years but decided to give up the role in 2003. I therefore stepped in and have run them in the subsequent years. My reason for doing so was not a great love of craneflies and fungus gnats, but instead a feeling that we would be losing a valuable event that has played a big part in our understanding of the autumnal fauna of the British Isles.

Initially, I followed the preceding model, which was a four-day event in mid to late October. The weather at this time is rather variable, so the dates have moved towards mid October starting on the second Saturday of the month or around 14 October (whichever is closer to the middle of the month). I also changed the format so that we spend a week in the field. My thinking is that there is that a lot of time is spent travelling and it is generally not practical to visit more northerly locations for just three or four day's fieldwork that might get rained off for part of the time. So, we now tend to go for a week, and often use two centres in order to improve coverage. Figures 1 & 2 show where we have been since 2004.

Figure 1. Autumn Field meeting coverage 2004 to 2012

Figure 2. Autumn field meeting coverage 2013 to 2017

Participants in the Autumn meeting are a fairly tight-knit group - very few people want to visit wet dank woods at the end of the season! So, in most years we only get six to eight participants. Also, we tend to attract people with interests in a wider range of disciplines; not just Diptera. I think this is very positive because the team makes a much broader contribution to the data on autumnal insects in far-flung parts of the country.

In a further change, I introduced the idea of supplementary meetings in late August or early September to cover Scotland where Autumn comes a lot earlier. Thus, in 2017 we found ourselves gathered at the Bay Tarbet Hotel on the west side of Loch Lomond. There were six of us: Peter Chandler (Fungus Gnat Recording Scheme), Alan Stubbs (Cranefly Recording Scheme), Andrew Halstead (Symphyta and many other Orders), Keith Alexander and Janet Lister (Saproxylic Coleoptera and Bark Bugs) plus me. On these trips I act as a parataxonomist and simply hoover vast numbers of Nematocera that I then sort into separate piles for Alan and Peter. I usually retain a residue of a few families such as Heliomyzids and Lauxaniidae and will of course log hoverflies when I come across them.

On this trip, hoverflies were comparatively abundant (figure 3) so I did assemble a reasonable number of records. Nevertheless, it is clear from the data that a small number of species made up the bulk of the records and that there was a comparative dearth of interesting species. That does not matter because coverage of common species can be useful and we did get a very good picture of what is flying at this time of year.
Figure 3. Numbers of records of hoverfly species recorded during the DF field meeting based at Tarbet from 8 to 15 September 2017.

In the course of six days (we lost one day to rain) we managed to visit 21 10km squares within a 50 mile radius of Loch Lomond (Figure 4)  and got a good feel for the fauna of the area. We visited a great many more 1km squares, often having to stop at two or more points within individual 10km squares in order to get anything like an adequate sample. Thus, the data I already have assembled covers more than 40 data points. Stopping points can rarely be considered to be sites; rather, they are points where it was possible to park the car and access suitable habitat. We tend to look for wooded streams and wetlands, as these are the most suitable for gnats and craneflies.

I think some of the ecological reflections are best left to a further post, as there is a need to try to interpret some of the results. Not all of the material has been worked-up and Peter has a large volume preserved in alcohol. Alan has done most of his specimens and tells me the species list is a bit over 50 species of cranefly and associates. There is one possible highlight - I took a specimen of a Tipula that Alan is unsure about. It may prove to be something that is already known but there is an outside chance that it is an addition to the British list - I wait in eager anticipation. Thankfully it is a male so it ought to be identifiable.

Figure 4. Locations visited during the 2017 DF meeting based at Tarbet. Note the three more southerly squares are visits made on the journey north on 7 September.

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