This note by Simon Tonkin and Juan Miguel Gonzalez Perea recently appeared in Brit. Birds 112 686–687 – You can view the original by clicking the link.
On 2nd January 2017, Simon Tonkin found a Yellow-browed Warbler Phylloscopus inornatus in the village of El Pelayo (near Tarifa), in Andalucia, Spain. The bird was subsequently present in an area of Cork Oaks Quercus suber for around six weeks and was presumed to have overwintered. Later that year, two Yellow-browed Warblers were found in the area, one on 30th October 2017, at the same site as the first, and the second on 1st November 2017, no more than 500 m from the first. One of these overwintered and, on 28th January 2018, was trapped and ringed by JMGP. It had a fat score of 0 (on a scale of 0–3) and a muscle score of 2 (scale 0–8; Redfern & Clark 2001), levels which suggest a wintering bird rather than an active migrant. Then, on 4th November 2018, ST found a ringed Yellow-browed Warbler in El Pelayo; on closer examination of the photos, the ring number was confirmed to be that of the ringed bird from the previous winter.
This observation is the first ringing recovery of Yellow-browed Warbler that confirms winter site fidelity in Europe and supports the hypothesis that this species is developing a new migration strategy and is now wintering regularly in the Western Palearctic (Gilroy & Lees 2003; de Juana 2008; Alfrey 2017a,b). This hypothesis could, at least in part, explain the massive increase of individuals in Britain in autumn (see White & Kehoe 2018, and earlier Scarce Migrant reports), which in turn could be related to new breeding grounds and/or population increase in the boreal forests of Siberia. It is now widely believed that these birds arriving in Europe are mainly juveniles on exploratory migration.
Until recently, Yellow-browed Warbler was a rare visitor in the Iberian Peninsula with only 95 accepted records between 1985 and 2011 for mainland Spain, mainly in late autumn/early winter (Juana & Garcia 2015). However, more recently sightings have increased markedly and the species is now reported regularly from favoured sites in Andalucia. The upsurge in records cannot be accounted for by changes in the numbers of potential observers and the pattern does appear to match the overall increase in numbers recorded in northwest Europe. Differences in mean arrival date with latitude in western Europe suggest that just a small proportion of birds arriving in Scandinavia and the UK move on through the Iberian Peninsula. It is also possible that birds appearing in potential wintering areas in Iberia and North Africa could arrive on a wide front across mainland Europe.
Sightings of Yellow-browed Warbler across Europe in the winter of 2018/19 shows birds discovered in a broad arch from Britain and Ireland across Iberia and into Macaronesia clearly indicating a wintering meta-population, which included over 50 birds wintering in southwest England alone in early 2019. Further ringing recoveries to confirm the establishment of a returning wintering population in Europe are still lacking and, as yet, satellite tracking of small passerines is still limited by the size and expense of the tags. Although good numbers of Yellow-browed Warblers are ringed each autumn in northwest Europe (over 4,000 in the UK to the end of 2018; BTO), the ring recovery rates of small passerines are extremely low; Robinson et al. (2011) showed the ringing recovery rate for Willow Warbler P. trochilus is only 0.001% with an annual survival of 31%.
We thank Peter Alfrey for his expertise, input and discussions about migration pioneers over many years and his direct review and discussion regarding this observation; Alex Lees for supplying e-bird data and Dawn Balmer for supplying the BirdTrack map; and the efforts of the Tumbabuey Ringing group.
Alfrey, P. 2017a. Migration: the pioneers https://www.birdguides.com/articles/general-birding/migration/migration-the-pioneers/?fbclid=IwAR33aXncY0UIvFByNT-P0T-6OBe8byPtTt2TSocsG-PoNMTAjf4f2SdOdlM
–– 2017b. Migration: fate or free will? https://www.birdguides.com/articles/general-birding/migration/migration-fate-or-free-will/?fbclid=IwAR0htwaqMKnVe18OglqXZikHQNVtfscoVQwlj2FFkI6T7UXoVGiqKpKPyU8
de Juana, E. 2008. Where do Pallas’s and Yellow-browed Warblers go after visiting northwest Europe in autumn? An Iberian perspective Ardeola 55: 179–192.
–– & Garcia, E. 2015. The Birds of the Iberian Peninsula. Helm, London.
Gilroy, J. J., & Lees, A. C. 2003. Vagrancy theories: are autumn vagrants really reverse migrants? Brit. Birds 96: 427–438.
Redfern C. P. F., & Clark J. A. 2001. Ringers’ Manual. BTO, Thetford.
Robinson, R. A., Grantham, M. J., & Clark, J. A. 2011. Declining rates of ring recovery in British birds. Ringing & Migration 24: 266–272, DOI: 10.1080/03078698.2009.9674401
White, S., & Kehoe, C. 2018. Report on scarce migrant birds in Britain in 2016: passerines. Brit. Birds 111: 519–542
Simon Tonkin and Juan Miguel Gonzalez Perea.