Warblers-Marmite birds?

I am always working on my website, my current project is to illustrate every bird on Category A of the British List. I am quite a long way in, and have come to "old world" warblers.  Like gulls, warblers, particularly Phyllosopus, seem to either provide great interest and a challenge, or are something to be ticked and then forgotten. I used to be somewhat in the latter group, but researching for my website has thrown up many interesting facts about vagrants to Britain. 

Many firsts for Britain in the 21st century have been warblers, including Eastern Crowned,  Pale Legged Leaf and Olive-tree. Several have been as a result of splits, and older records were rarely assigned to the relevant subspecies. This is rarely important since few records exist, and they can be re-examined, however in the case of Subalpine Warblers it really isn't possible. Adult male birds aren't too bad, but females and immatures can be impossible to assign to one or other taxa in the field. A recent case in point is a bird on Shetland, which I saw, but it was only ever quite distant and often elusive. It was always reported as an Western Subalp., despite being there for nearly two weeks no-one queried its identity. However, it seems DNA was obtained, I don't know how but after I had left it became more obliging. A couple of weeks later the DNA findings were reported- it was Eastern. I make no comment about this, I saw all three species long ago, but it does illustrate the point that they can be indistinguishable and older records may not be accurate except in the case of adult birds.

 What I find even more interesting is that we are obviously getting more records of warblers, and this is partly due to splits and improved methods of identifying them. Birds like Olivaceous Warblers are slowly building up records, probably due to increased observer coverage, but in this case the birds closer to home which migrate south are in the minority (one) with most records coming from the Eastern Mediterranean and beyond (nearly thirty). Obviously some older records weren't assigned to a taxon, but officially the first Western wasn't until 2023. Just glad I've seen both abroad. It seems to me that direction and time of migration obviously have a bearing, but also many species from further afield,  such as Yellow-browed Warbler, may be "prospecting" and could breed here one day. Pallas's Warbler was once a mega rarity in the same way that Pale-legged Leaf is now, and there are more species of Phyllosc. to come. You may think there won't be another Sulphur-bellied Warbler, but never say never.....

Many splits could potentially give rise to problems of assigning birds to a species, but thankfully in most cases only one of a complex is a likely migrant. I am thinking here of Arctic Warbler, which has two cryptic species, Japanese and Kamchatka Leaf Warblers. The only way to distinguish them is DNA or vocalisations, indeed I had a photograph of an Arctic Warbler labelled as such for years, but it was a breeding Kamchatka Leaf Warbler, taken in southern Kamchatka. I can't prove it, but the location is a clue! And are they really not likely migrants? I don't think so, but no-one really knows. At present several species have been initially identified as Arctic until the call is heard, so we really should check them all. Unfortunately I'm deaf (ish), but Apps can be used, providing the bird calls!

So I'm beginning to like Old World Warblers, it's only taken forty years! I've not even mentioned Zitting Cisticola, which used to be called Fan-tailed Warbler when I first saw one at Portland.