IRBC - Announcements

Blyth's Reed Warbler, 2003.


The sole Irish record of Blyth's Reed Warbler Acrocephalus dumetorum to date concerns a bird seen at Cape Clear Island, Co. Cork from 13th to 19th October 1969. The descriptions have been published in full in the Cape Clear Bird Observatory Report No. 11 (1969) pp. 34-38.


This record has attracted considerable attention over the years, as it was the first record of a Blyth's Reed Warbler in Britain or Ireland identified solely on the basis of 'in-the-field' views; it was neither trapped nor photographed, so the record lacked any of the biometric data which at that time would generally have been considered a prerequisite to safe identification of an autumn vagrant anywhere outside its normal range. It is testimony to the then growing confidence in new, often largely 'jizz-based', identification criteria that not only was this record accepted, but that the observations of this particular bird provided the material for a note boldly entitled "The identification of Blyth's Reed Warbler in autumn" (Sharrock et al 1970). Since then, much has been written about Blyth's Reed Warbler and the complexity of its identification e.g. (Harvey et al 1984), (Harrap 1989) and some authors have questioned aspects of the identification of this bird and the validity of some of the features regarded by Sharrock et al as diagnostic of Blyth's Reed Warbler. Of the 29 records of Blyth's Reed Warbler in Britain up to 1995, only one was of an autumn bird that was not trapped (Rogers et al 1997; Evans 1994). Indeed, it was not until as recently as 1996 that there were signs of significantly increased confidence in the field identification of autumn vagrants (Golley & Millington 1996; Rogers et al 1997).


Blyth's Reed Warbler is actually very similar to both Reed Warbler and Marsh Warbler in the field and conclusive identification of autumn birds in the field requires very critical observation and close attention to vocalisations.


Key features that aid in the identification of Blyth's Reed Warbler in the field can be summarised as follows (adapted from Golley & Millington 1996):-


  • Short primary projection
  • Sylvia-like call
  • Prominent fore-supercilium
  • Emarginations on third and fourth primaries
  • Greyish toned legs
  • Comparatively little contrast in wing-feathers
  • Lack of contrastingly ginger rump

A number of features noted on the Cape Clear bird do, it has to be said, correspond with what are now regarded as significant indicators of Blyth's Reed Warbler in the field, namely the longer bill, the colder brown upperparts lacking rufous tones and the short wings. On the other hand, it is disturbing that the bird is described as having been so different from a typical Reed Warbler when, in reality, the two species are extremely alike. The descriptions all emphasise the prominence of the tail (described as 'huge and rounded') and bill length (described as 'gigantic') and while it seems likely that there is an element of exaggeration in these accounts it nevertheless adds to the difficulty in reconciling what is described with the undeniably subtle character of Blyth's Reed Warbler. In addition, the repeated emphasis on a lack of any supercilium suggests something other than Blyth's Reed, while the inconclusive descriptions of the bird's call (unfortunately, it was heard to call on only one occasion) do not lend significant support to the identification.


The IRBC concluded that while it was quite possible that the bird was in fact a Blyth's Reed Warbler, that there was insufficient firm evidence to support the identification of this notoriously tricky species. Consequently, Blyth's Reed Warbler has now been removed from the Irish List.


References:

Evans, L.G.R. 1994. Rare Birds in Britain 1800-1990. Privately published.

Golley, M. & Millington, R. 1996. Identification of Blyth's Reed Warbler in the field. Birding World 9: 351-353.

Harrap, S. 1989. The difficulties of Reed, Marsh and Blyth's Reed Warbler identification. Birding World 2: 318-324.

Harvey, W.G. & Porter, R.F. 1984. Field identification of Blyth's Reed Warbler. British Birds 77: 393-411.

Rogers, M.J. et al. 1997. Report on rare birds in Great Britain in 1996. British Birds 90: 453-522.

Sharrock, J.T.R., Hutchinson, C.D., Preston, K., & Barbier, P.G.R. 1970. The identification of Blyth's Reed Warbler in autumn. British Birds 63: 214-216.


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