Pale-legged Leaf Warbler: new to Britain John Headon, J. Martin Collinson and Martin Cade Abstract A Pale-legged Leaf Warbler Phylloscopus tenellipes was discovered dead after hitting a window at the lighthouse on St Agnes, Isles of Scilly, on 21st October 2016. Feathers taken from the bird were sent for DNA analysis, which confirmed the bird to be a Pale-legged Leaf Warbler and eliminated the morphologically similar Sakhalin Leaf Warbler P. borealoides. An earlier record of one of this species pair from Portland, Dorset, on 22nd October 2012 concerned a bird photographed and seen well by several observers, but it was not possible to establish which species was involved. Full details of both sightings are described here. This is the first record of Pale-legged Leaf Warbler for Britain and the Western Palearctic, and the species has been added to Category A of the British List. Pale-legged Leaf Warbler on Scilly t around midday on 21st October point Pale-legged Leaf P. tenellipes and 2016, Laurence Pitcher (LP) was Sakhalin Leaf Warbler P. borealoides were not A eating a pasty outside the lighthouse species that crossed my mind, but several on St Agnes in the Isles of Scilly when the people responded immediately – notably owner, Fran Hicks (FH), came over for a James Gilroy, Chris Batty and Andrew Holden chat. They bemoaned the lack of migrants on (AH) – with these very suggestions. AH hap- the island, but in parting FH casually men- pened to be on the island and soon arrived at tioned that a Phylloscopus warbler had struck the lighthouse. Over the phone he was able to his conservatory window earlier that check the wing formula and go through some morning and sadly died. FH added that other features with Chris Batty, who was although it resembled one of the Yellow- giving pointers from Williamson’s Phyllo- browed Warblers P. inornatus that had been scopus identification for ringers guide frequenting the lighthouse garden, there were (Williamson 1976). This established beyond aspects of its appearance that were niggling doubt that the bird was either a Pale-legged him. That could well have been the end of Leaf or a Sakhalin Leaf Warbler. There is as the story but, since FH was returning to his yet no reliable means of separating these two garden, LP casually asked if he could see the species in the hand, or in the field unless they dead warbler. FH quickly reappeared, holding are singing or calling. But DNA testing could the corpse. LP takes up the story: conclusively establish a final identification, ‘The bird was not a Yellow-browed and my and whichever species it was, this would thoughts turned to Greenish P. trochiloides or become the first proven record of that species Arctic Warbler P. borealis. I dismissed in the entire Western Palearctic.’ Greenish but something was not right for This clearly wasn’t a conventional ‘bird Arctic either. I couldn’t reconcile the primary find’; instead it was more of a cooperative projection, and the bird’s bill seemed odd, but effort by the wider birding community and the I admit to overlooking some obvious input of all those involved is greatly appreci- plumage features. I decided to circulate ated. The dead bird was given to Nigel Hudson images on Twitter, hastily captioned “Arctic (then the BBRC Secretary) for safekeeping in Warbler?” and inviting comments. At this his freezer on St Mary’s, which enabled many 438 © British Birds 111 • August 2018 • 438– 445 Pale-legged Leaf Warbler: new to Britain Laurence Laurence Pitcher 298. Pale-legged Leaf Warbler Phylloscopus tenellipes, St Agnes, Isles of Scilly, 21st October 2016. birders on Scilly to pay their respects. The body field only and at present the difficulties of was sent to the British Museum, Natural distinguishing between Pale-legged Leaf and History, at Tring for preparation. Sakhalin Leaf Warblers make it impossible to take this identification further. It is perhaps Discussion ironic that all birders on Scilly at the time There has been one previous example of this would have preferred to see this bird alive, species pair, at Portland, Dorset, in October but if that had happened it would not have 2012 (see below). That bird was seen in the been possible to identify it to species! Biometrics and wing formula The following biometrics were taken by Jim Askins at Carn Ithen, Old Town, St Mary’s, on 23rd October 2016. Wing length 61 mm Tail length 45 mm Bill (to skull) 12.5 mm Bill (to feathering) 10 mm Bill width (proximal end nostril) 3 mm Bill depth 2.5 mm (slightly damaged) Tarsus 18 mm Hind claw 5.5 mm Weight 9.8 g Fat score (scale 0–8) 3 Muscle score (scale 0–3) 2 Primary-tip shortfall (mm) measured relative to wing point (WP = longest primary), apart from P1, which is measured relative to primary coverts; e = emarginated primary. P1 P2 P3 e P4 e P5 e P6 e P7 P8 P9 P10 PC+6 -9 -1 WP -1 -3 -7 -9 -11 -15 Length of each individual tail feather (mm). R6 and R5 showed a white inner tip. R6 R5 R4 R3 R2 R1 43 45 44 44 44 41 British Birds 111 • August 2018 • 438– 445 439 Headon et al. Fig. 1. Phylogenetic tree based on the COI gene for the ‘Scilly Phyllosc’ alongside individuals of Phylloscopus tenellipes and P. borealoides from breeding areas, as well as other superficially similar taxa (Arctic Warbler P. borealis, Kamchatka Leaf Warbler P. examinandus and Japanese Leaf Warbler P. xanthodryas). Nodes in red have >99.9% bootstrap statistical support. They delineate a robust split between the borealoides individuals (in blue) and the tenellipes individuals (in yellow), and confirm that the Scilly bird was a Pale-legged Leaf Warbler. DNA analysis Scilly bird was genetically highly divergent Two small feathers from the bird were sent to from borealoides (and all other species) and JMC for analysis. DNA was extracted using almost identical to previously sequenced the QIAGEN DNA Micro Kit according to individuals of tenellipes. For example, at the manufacturer’s instructions. Genetic sexing COI gene, it was within 2–5 bp (out of 711 using both the P2/P8 and 2550F/2718R PCR bp) of 13 tenellipes, and at least 27 bp (3.8%) primer sets (Griffiths et al. 1998; Fridolfsson different from any of 15 borealoides. Any & Ellegren 1999) yielded single (Z chromo- database birds sampled away from their some) bands, indicating that the bird was breeding grounds were then excluded from a male. The cytochrome b mitochondrial the analysis to avoid circular reasoning (most gene (cytb) was amplified using the had been identified on DNA), and phyloge- L14993/H16065 primers (Helbig et al. 1995) netic trees drawn up using ‘Neighbour and the cytochrome c oxidase subunit 1 gene Joining’ and ‘Maximum Likelihood’ method- (COI) using the primers BirdF1/BirdR1 ologies – they all told the same story and (Hebert et al. 2004). Both genes were placed the ‘Scilly Phyllosc’ in the tenellipes sequenced and were compared with database group with >99.9% statistical support. A rep- sequences of tenellipes and borealoides previ- resentative tree is presented as fig. 1. The COI ously obtained by other groups from the sequence was submitted to Genbank, with breeding and wintering grounds. It became accession number MG917724. immediately obvious for both genes that the John Headon*, Hivernia, Jackson’s Hill, St Mary’s, Isles of Scilly TR21 0JZ; e-mail [email protected] J. Martin Collinson, University of Aberdeen, School of Medicine, Medical Sciences and Nutrition, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD; e-mail [email protected] * John Headon has compiled this article in his capacity as the Isles of Scilly Recorder and would like to emphasise that he was not involved in the identification of this bird. 440 British Birds 111 • August 2018 • 438– 445 Pale-legged Leaf Warbler: new to Britain Pale-legged Leaf Warbler or Sakhalin Leaf Warbler in Dorset onday 22nd October 2012 was a mind the enormous interest there would be day when perfect fall conditions from the birding community, it was agreed Mdropped a major arrival of birds on that if the bird was present in the morning I the Isle of Portland, Dorset. Pete (PS) and would attempt to trap it and release it in a Debby Saunders were, as usual, attentive to the suitable nearby spot where it might be acces- comings and goings in their garden at South- sible for general viewing. well and, with one or two Yellow-browed War- In the event, further research quickly blers already seen that morning, they were revealed that the identification was not as alert to rarity possibilities. Towards midday, PS straightforward as I had originally thought: had a brief glimpse of a Phylloscopus warbler initial indications that Pale-legged Leaf with a striking supercilium in low vegetation Warbler might be separated from its sister beside the garden pond. Being unable to put a species, Sakhalin Leaf Warbler, by, for name to it, he summoned assistance from example, the presence of strong wing-bars Grahame Walbridge, who was birding nearby; (del Hoyo et al. 2006) or paler legs (Brazil on arrival, Grahame suggested that the bird 2009) were contradicted by other sources. It might be an Eastern Crowned Warbler P. coro- was soon apparent that the two species may, natus. With only two previous British records, in fact, be separable only by subtle morpho- it was quickly apparent that there would be logical features, by song, or by genetic exami- considerable interest in the bird and local nation (Carey et al.