Friday, 14 July 2017

updated hoverfly records

All of the data extracted and received for 2016 have now been uploaded into the HRS database. They largely speak for themselves but I thought it was worth doing a short piece to explain the graph and maps. Almost 52,000 records were added this week, mostly covering records from 2016 but also a few dating as far back as 2005.

The headline really should real HRS reaches 1 million records, but we fall a bit short of it officially (there are about 5,000 2016 personal records on my database still to go in). As it stands, the database currently holds 994,838 records. There is about 10% duplication within the dataset so the true number of 'unique' records is probably about 900,000. That leaves us a bit short of the million in strict terms but at the current rate 1 million 'unique' records should be achieved within the next two years, and 1 million records in total will be reached very soon – just as soon as I sort myself out and download my data to Stuart (just over 5,000 records for 2016 and a further 3,000 for 2017). I will also pass on the data I hold for 2017 so I suspect the total will reach 1,010,000 records in a few weeks time. The other big omission from these data is records submitted to LRCs - at some point Stuart will do a trawl of new data on the NBN.

This upload included MapMate synchs but not data on iRecord which we have still to work out what to do with. iRecord data cause us a bit of a problem because a LRC that shall be nameless uploaded its entire dataset and flooded it with data that we already have but that now we are not sure which to use – there is an awful lot of cross-checking to do before we can extract those data that are genuinely new and those that are re-determinations and queries. Even so, I think there are probably around 12,000 further records within iRecord to incorporate.

The most obvious feature of the data is the dramatic rise in the number of records received since 2013. The top four peaks for the most records received fall into the years 2016 (53,669); 2015 (48,708); 2014 (41,917); 1987 (39,442) respectively. We know the 1987 peak was stimulated by a 'call for records' in advance of atlas production that took a further 13 years to materialise!
Figure 1. Total yearly records within the database. The HRS was launched in 1976 and a major boost to recording occurred with the publication of Stubbs & Falk in 1983.
The current peaks can be attributed entirely to the UK Hoverflies Facebook group. It really goes to show what can be done when schemes encourage participation by people who might not be traditional recorders. As I recall (without going back to data) data extracted from FB probably comprises about 60% of the data received in the last few years (I must get Stuart to do a chart). This is reflected in the numbers of contributors to the dataset, up from 8,482 in 2016 to 8,865 now.

Coverage in 2016 shows that there is much more to do, with most recording concentrated in England. To a great extent this reflects the centres of population which inevitably means that recording effort will be more concentrated. A lot of Central Wales is both sparsely populated and difficult to work because easily accessible sites are more scattered and the geology is unhelpful (very poor acid conditions that limit species diversity). The same holds for much of Scotland, but it does surprise me just how few records we get, comparatively speaking.

The coverage maps are, however, simply a snap-shot of one year's effort and over a series of years the gaps do get filled in to a large extent. Nevertheless, there will be parts of the county where there will always be a shortfall in coverage without deliberate 'square-bashing' – something I have tried to do over the years, but I fear my efforts will be severely curtailed for the foreseeable future.
Figure 2. Record coverage (all sources) for 2016.
Figure 3. Number of species recorded from individual 10km squares in 2016.

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