This is one of many Conservation Designations, all used in the Planning processes to help conserve wildlife. The IUCN Red List is the most useful and informative one for us. A whole bunch of people have spent a lot of time putting together the lists for Diptera over the past years. They didn’t use actual recorded data much though, just published papers, which meant that all the categories had to be prefixed with “provisional”. In Bulletin 83 (p8) I gave a thumbnail method for using actual records to reassess their IUCN status. They are scheduled for reassessment in 2022, the plan being to redo them every 10 years.?
The actual detail of how the categories are assigned are in a book: ?IUCN, 2012. IUCN Red List Categories and Criteria. Gland, Switzerland. (DOI 10.9782-8317-0633-5) ?which I guess was pored over when Steve Falk and others compiled our own Diptera Red Lists.
You’ll find all of them listed under Conservation Designations for UK taxa on the JNCC website at https://tinyurl.com/y2shz72q where they are listed in chronological order, just scroll down and download each one, they are packed with useful information about all our scarce species.?
Before I get lynched by all those authors at the suggestion that they’ve got to start thinking about doing them all over again, let me point out that at the time the original Red Lists were drawn up, there was little in the way of published species occurrences on GBGs (NBN Atlas as it is now) but ten or more years has seen an enormous increase in the quantity and quality of this data. It seems likely therefore that any amendments and updates may be achieved by using this data.?As yet the mechanism for producing such updates is unclear.
What is clear however is that Recording Schemes have a strong role and that by ensuring that their datasets are brought up to date (2020) and, ideally, uploaded to the NBN Atlas, their contribution to conservation will be assured.