Tuesday, 2 September 2014

Subalpine Surprises

Subalpine Warbler is a scarce migrant to Fair Isle with 85 records (including the five this year that await formal acceptance by the relevant committees). All bar four have been seen in the spring and there have been 50 males, 31 females and 3 left unsexed.
So far, so simple, but various papers have been published looking at the relationships of the differing subspecies found within the Subalpine Warbler complex, culminating in Lars Svensson (2013) proposing a three-way split, namely:

Western Subalpine Warbler Sylvia inornata, comprising S.i.inornata of northwest Africa and S.i.iberiae of Iberia and parts of southern France and northwest Italy. The males of this species are generally extensively orange-brown below and both sexes show a small, rounded white tip to the second outermost tail feather (T5).

Eastern Subalpine Warbler Sylvia cantillans, comprising S.c.cantillans of southern Italy and S.c.albistriata of northeast Italy, Greece, western Turkey and the Balkans. The males of this species are generally brick-red on the throat (more orange on S.c.cantillans) and upper breast, with usually a more distinct cut-off from the white breast than Western Subalpine Warbler. T5 shows a distinctive pointed white wedge.

Moltoni’s Warbler Sylvia subalpina Found in Corsica, Sardinia and northern Italy, the males are more salmon-pink below than the other species and both sexes show a similar tail pattern to Western Subalpine Warbler, making identification of females a somewhat unknown quantity.

Most of the Fair Isle records are currently unassigned to any of the three species (being accepted as ‘Subalpine Warbler’), but prior to this year, at least 13 had been attributed to Eastern Subalpine Warbler. [It’s worth noting that the recent taxonomic work has seen the various scientific names changed around a bit (cantillans previously being used for Western birds for example).]
Annual records of Subalpine Warbler on Fair Isle (there is also a record from 1908). The species is now a virtually expected scarce annual migrant on Fair Isle, with the last blank year back in 1999.
This year has been a very good one for Subalpine Warblers on Fair Isle, with five birds recorded. One of these (a male at Schoolton on 13th June), wasn’t trapped but was a fairly clear Western Subalpine Warbler based on the extent and tone of the colour of the underparts and the tail pattern.
The Schoolton bird showed very well (often alongside a Blyth's Reed Warbler!).
A bird at Burkle from 3rd May to 21st May also showed the underpart colour and tail pattern (and also call) of Western Subalpine Warbler.
The Burkle bird was heard singing on several occasions and was typical of the extended stay of several individuals of this species in recent years on Fair Isle (photo by Deryk Shaw).
DNA analysis of the other three birds has thrown up some surprising results:

First of all was a bird trapped late in the evening of 25th April, which lingered to 2nd May, although it was rather elusive as it toured the island and was seen on only three dates during this spell. It was largely lacking its tail when it was found, although the regrowing feathers appeared not to show any white wedge. The restricted pinky throat patch appeared a closer match to Eastern though and given the damage to the tail, it was provisionally identified as such, with the knowledge that a DNA sample would be able to confirm (or otherwise) the identification, allowing the bird (caught just before dusk and very light, presumably having just arrived on the island) to be released as quickly as possible. The DNA results have now come back and showed the bird to be a Western Subalpine Warbler after all.
Note the typical tail pattern of Western Subalpine Warbler, but the pinkish colour restrictedto the throat and upper breast, more typical of Eastern. The lighting in the ringing room may well have effected the apparent tone of the pink colour.
A male identified in the field as Eastern Subalpine Warbler on 8th May was trapped in the Gully and the identity confirmed by the distinctive tail pattern. DNA analysis went a stage further though and showed it to belong to the subspecies S.c.cantillans, the first confirmed record of this subspecies in Britain. DNA analysis of the first British specimen of Eastern Subalpine Warbler (a male collected on Fair Isle in May 1908) showed it to belong to S.c.albistriata (Collinson et al 2014), so Fair Isle now boasts the first British records of both subspecies of Eastern Subalpine Warbler.
It's interesting to compare the extent (and tone) of the underpart colour of this Eastern bird compared to that of the Western bird above. This subspecies was previously lumped with Western birds and, apart from showing the distinctive tail pattern of Eastern, it is easy to see why.
Finally, a female trapped on 16th May, which lingered at the Obs until 27th May showed the rounded white tip to T5 that suggested it was a Western Subalpine Warbler, however, DNA analysis has proved that the bird was a MOLTONI'S WARBLER. There is currently only one accepted record of this species from Britain, a bird collected on St Kilda in 1894 that was identified from DNA analysis (Collinson et al 2014), with two further records (both from Shetland in spring 2009) currently being assessed by the BBRC (Stoddart 2014).
Presumably, Moltoni's Warbler has been overlooked in the UK, especially as females are apparently virtually identical to Western Subalpine Warbler. However, since a popular bird on Unst in 2009 that brought the key identification features  (particularly of the distinctive males) to the attention of many British birders, I'm not aware of any other claims of Moltoni's, which suggests that they may well still turn out to be rather rare. 
Assuming that the three-way split is adopted by the BOU, this will prove to be a bonus tick for anyone who enjoyed this showy little bird (and adds to the already very impressive list of very rare birds recorded on Fair Isle in the spring).
So, a somewhat surprising turn of events and an example of how birding is being aided by advancing technology. Perhaps we may be able to contribute to using confirmed records such as these to try to identify ways in which female Moltoni’s may be identifiable in the field (the distinctive Wren-like rattling call of this bird was not heard).

The next stage for FIBO is to try to identify as many of our previous records as possible, which is where we are appealing for help from anyone who has photographs (particularly of the tail pattern), field notes or sound recordings of any records of Subalpine Warbler from before 2011 (or the female in April 2011). Please get in touch if you do as we’d love to be able to attribute as many of our previous records as possible to the correct species.

Many thanks to Professor J.Martin Collinson for the work on the DNA analysis and, of course, to my Wardening team and the others who were responsible for finding the birds in the first place!
Collinson, J.M., McGowan, R.Y. & Irestedt, M. 2014. First British records of 'Eastern' and 'Western' Subalpine Warblers. Brit Birds 107: 282-297
Stoddart, A. 2014. Assessing and recording Subalpine Warblers. Brit Birds 107: 420-424
Svensson, L. 2013. Subalpine Warbler variation and taxonomy. Brit Birds 106: 651-668

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