DOMINIC MITCHELL For the record

Rarities committees do a great job of assessing records based on evidence submitted by observers. In the case of national firsts, wonders Dominic Mitchell, should that always include a photo?

Autumn is prime time for rarities in Britain, and if anyone needs reminding of the exciting possibilities at this time of year, look no further than the report of the British Birds Rarities Committee. This is a comprehensive summary of all submitted records of national rarities from the preceding 12 months (plus a few older records).

The report should be required reading for all those with an interest in rarities – not just to see what has been accepted (or deemed not proven) and to digest the occurrence patterns and statistics, but also to gain insight into the evidence required for the assessment of such potentially difficult species as Iberian Chiffchaff, the subalpine warbler complex and Eastern Yellow Wagtail.

One aspect of this process that has become apparent over the years is the growing reliance on images. Aesthetically, of course, they always bring the report to life, and the latest is no exception, with photos of – to name just a few – first-winter male Steller’s Eider, a fly-by Common Nighthawk, Great Knot in breeding plumage and, more quirkily, that Tengmalm’s Owl on a toilet seat. But their real importance is in allowing committees to assess critical details that are often not discernible in the field.

Subtle subspecies

Two cases in point in this latest report both refer to first British records of subtle subspecies of more familiar birds. The Mandt’s Black Guillemot (subspecies mandtii) in Lincolnshire for four days in December 2017 would surely not have made the grade but for the photos scrutinised by the committee, which the report explains “enabled the precise extent of white in the primaries, wing coverts, scapulars and rump to be confirmed”. A written description based only on sight views is unlikely to have been enough for this level of forensic proof.

Similarly, the first British Taiga Merlin (of the nominate northern North American form columbarius) was seen just twice in Caithness in February 2018, but also photographed.

Again, the features are subtle, but Nearctic

Birdwatch and Scarce Bird Report,

Photos play an increasingly important role in rarity recording, enabling committees to assess not only the finer points of identification but also, in cases such as this much-discussed Dusky Thrush in Kent in May 2013, whether or not any subtle hybrid influence might be discernible.