Olivaceous Warbler Review, 2003.

Several factors have prompted a review of the Irish records of Olivaceous Warbler:

• Criteria for the separation of the two forms of Olivaceous Warbler that occur in Europe have become clearer and, more recently, most authorities have recognised that not only are the two forms, Hippolais (pallida) elaeica and Hippolais (p.) opaca clearly distinct, but that they are better regarded as two separate species - respectively known as Eastern Olivaceous Warbler H. pallida and Western Olivaceous Warbler H. opaca.
• The separation of Eastern Olivaceous from Booted Warbler H. caligata of the form rama has recently received a lot attention in international identification forums. In the past, rama was considered an unlikely vagrant to western Europe, but with several recent occurrences in Europe of birds assigned to this taxon there was clearly a need to consider the possibility of rama being involved in the Irish records of Olivaceous Warbler. During the course of the review, a major paper on the topic was published and strong evidence was put forward that rama too should be regarded as a full species rather than a race of Booted Warbler (Svensson, 2001). This proposal has recently been formally adopted by the BOURC Taxonomic Sub-committee and the newly recognised species is now known as Sykes's Warbler H. rama.

Unlike the records involved in some of the other reviews detailed above, all records in this review concern birds that were either trapped or very critically examined and photographed in the field. Hence more emphasis could be placed on interpretation of the data available, and less significance attached to trying to unravel subjective issues such as "jizz" from the accounts.

This review considered three of the previous records of Olivaceous Warbler in Ireland:-

• Tory Island, Co. Donegal, September 1959
• Dursey Island, Co. Cork, September 1977
• Cape Clear Island, Co. Cork, October 1990

The more recent record from Cape Clear Island in 1999 was specifically not included in this review as it had completed its original assessment in 1999/2000 when the Committee had access to considerably more information on the identification of Hippolais warblers than was the case with the earlier records. In light of further refinements in identification criteria since this assessment, it is now clear that the record is referable to Eastern Olivaceous Warbler, the form that breeds in southeastern Europe.

Following this review, only one further record of Olivaceous Warbler has been ratified as acceptable. Each of the records that were reviewed is discussed individually below.

Tory Island, Co. Donegal, September 1959

This was the first Irish record (and only the third record of Olivaceous Warbler for Britain and Ireland at the time). The bird was seen late in the afternoon of 29th September 1959. Having been watched in the field as it foraged on stone walls and frequently on the ground, it was trapped and examined (under artificial light) that evening. It was clearly a very interesting bird and to complicate matters, it was undergoing a moult of the tail at the time. Given the fact that the original account was never published in an Irish journal, it seems worthwhile to reproduce some of that account from British Birds 53:311-314 (1960), including the full description from the sole observer, RG Pettit.

"(The) initial impression was that it was something like a Northern Willow Warbler...distinctly Phylloscopus-like appearance... However,...it had a notable long bill and the high forehead of the Hippolais, and its carriage on the ground was rather pipit-like, with fairly long legs and a longish tail for a warbler.frequently perched on the tops of walls.. it was noticeable that it had a wagtail-like habit of flicking its tail. The wings were not especially long.

Upper-parts uniform dirty olive-brown; flight feathers and tail slightly darker, though the opposite effect was given in the closed wing by lighter edges to the primaries; slight light eye-stripe. Under-parts dirty grey, more olive at the sides of the breast; chin whiter. Legs horn colour with a bluish tinge (but none of the brightness of the Icterine). Bill fairly broad and distinctly long, with a heavy ridge effect along the top, the feathers growing down to the nostril on the sides but not on the ridge; bill colour dark brown above, pinkish below and very light on the flanges; inside of mouth bright yellow with orange veins. Eye grey-brown with dark pupil. Measurements: wing 62mm, tail 53mm, tarsus 20mm, bill 8.25mm from nostril and 15mm from skull with maximum width 5.5mm; two outermost tail-feathers 2mm and 6mm shorter than longest, and several others only half grown. Wing Formula; 4th primary longest, 3rd and 5th equal and fractionally shorter, 6th -3.5mm, 2nd -5mm, 7th -8mm, 8th - 10mm, 9th - 12mm, 1st 4.5mm longer than primary coverts. Weight 9.15gm."

Despite the reasonably full biometric data, it hasn't been possible to assign this bird to any of the likely species. The absence of detail as to emarginations on the primaries, together with an apparently incorrect measurement for either the wing-length, or the bill-width (since none of the candidates can have the combination of a wing of 62mm and a bill 5.5mm wide) present a real obstacle to matching this bird to any species. The width of the bill is more prone to being incorrectly measured than is the length of the wing, but we cannot be sure. At the time, the claim was submitted to the British Birds Rarities Committee and was independently assessed by the acknowledged expert of the time, Ken Williamson. The anomalies mentioned above were noted by Williamson, but the record was nonetheless deemed to be acceptable. In his assessment, Williamson seems to have compared the biometrics to both forms of Olivaceous, and to caligata Booted, but the possibility of rama may not have been considered at the time. In actual fact, the biometric data available, as well as certain aspects of the brief field description tantalisingly hint that this bird may well have been a Sykes's Warbler. In 1995 the BBRC commenced a review of previous British records of Olivaceous Warbler and, by virtue of the fact that the observer of the Tory bird had submitted the account to them, they included this record in their review. It was deemed unacceptable as an Olivaceous Warbler for the same reasons as outlined above.

Dursey Island, Co. Cork, September 1977

On 16th September 1977 a warbler was identified in the field by DA Scott as an Olivaceous Warbler before being trapped, examined and biometric details taken. It was then roosted overnight before being released. The record was submitted to the IRBC along with the measurements and some photographs taken of the bird in the hand and it was duly accepted on its first circulation (Irish Birds 1978: 1:267). On review, this bird is clearly an Eastern Olivaceous Warbler based on the combination of the described features and measurements. With the 1959 record no longer being acceptable, the Dursey Island bird now becomes the first Irish record of Eastern Olivaceous Warbler.

Cape Clear Island, Co. Cork, October 1990

When first found this bird's plain, sandy-coloured plumage immediately suggested that it might prove to be a Booted Warbler. Given the context of the bird's extreme rarity, the first observers were reluctant to plump for a firm identification until others with field experience of this species in Britain arrived. Doubts were then expressed, and gradually the weight of opinion swung away from identifying the bird as a Booted Warbler. The perceived wisdom of contemporary identification articles was that, based on the bird's frequent calling and tail movements, it was instead an Olivaceous Warbler. Although a little over a decade ago, no one was aware of the possibility of distinguishing between - as they were then - the two subspecies of Booted Warbler H. c. caligata and H. c. rama (now Sykes's Warbler) in the field. An account of the bird's discovery was published (McGeehan, 1990) and the following year the record was accepted by the IRBC as an Olivaceous Warbler.

Prompted by the finding and subsequent trapping of an apparently identical bird in Shetland in late October 1993, which proved to be a Sykes's Warbler, the belief in the Cape Clear bird really being an Olivaceous Warbler was steadily undermined. Since 1993, approximately ten rama have been identified in western Europe. There is remarkable similarity between these birds and the Cape Clear individual (most were trapped, and all were well documented with descriptions and photographs).

Photographic evidence yielded valuable information, principally relating to bill length and overall proportions, and the Cape Clear bird has now been accepted as a Sykes's Warbler. The reasons for this decision are summarised below. Further discussion of the Cape Clear individual's protracted identification history have already been published (McGeehan 2002).

In comparison with Eastern Olivaceous Warbler, the Cape Clear Sykes's Warbler differed chiefly in the following respects:-

• Overall pallid colouration, lacking strong plumage contrasts, and without olive or darker brownish tones in the upperparts.
• Thinner, straighter bill.
• Tail movements consisting of almost continuous twitching and flicking upwards after initial downwards motion. The tail was also flicked sideways. The wings were occasionally flicked in a manner suggesting a Phylloscopus warbler. Calling accompanied the tail and wing movements.

In comparison with Booted Warbler, the bird showed:

• A more bland head pattern, lacking well-defined darker sides to the crown.
• A longer, more dagger-like head and bill shape, somewhat suggesting an Acrocephalus warbler.
• A noticeably long, pale bill, to all intents lacking a discernible dark tip to the lower mandible.
• An obviously long-tailed/short-winged impression.
• A shorter, less pronounced supercilium.
• An overall, pale colour scheme lacking any richer brown or rufous tones. For example, the flank colour was whitish rather than brown-tinged.

The 1990 record therefore becomes the first Irish record of this species.

Summary

As a result of this review, there are now only two acceptable records of Eastern Olivaceous Warbler with the already accepted bird in Co. Cork in 1999 becoming the second Irish record. It is generally not a difficult species to identify if the views are satisfactory. It displays a relatively consistent appearance and, being the subject of many identification articles in recent years, there is no shortage of reference material available.

The separation of Sykes's from Booted Warbler is more challenging but, with adequate experience and good views, it should not prove too difficult. The recent series of records of Sykes's Warblers suggests that it will prove to be a regular, if very rare, wanderer to western Europe. Indeed, it seems likely that some earlier records of Booted Warbler from western Europe may be found to be referable to Sykes's Warbler, and its future status in comparison to Booted and to Eastern and Western Olivaceous Warblers may be significantly different than perceived at present.

As the characters and vagrancy pattern of the species will inevitably become better understood, perhaps one day it will be possible to reassess the Tory Island individual and reconsider it as a Sykes's Warbler. Equally, the door remains open for a re-evaluation of all apparent records of Sykes's and Booted Warblers, as and when the knowledge of the species improves (Svensson in Lee et al. 2002).

Acknowledgements

The IRBC would like to express its thanks to the following for assistance with this review: BBRC, Hannu Jännes, Anthony McGeehan, Richard Millington, Eamonn O'Donnell, Adam Rowlands, John Scovell, Lars Svensson, Reg Thorpe, DIM Wallace and Dan Zetterström.

References:

Lee, J., Brown, P. & Gray, M. 2002. The Sykes's Warbler on Orkney Birding World 15: 375-377.

Osborn, K. 1993. The Shetland Hippolais warbler. Birding World. 6: 438-438.

McGeehan, A. 1990. Olivaceous Warbler on Cape Clear, Co. Cork. Irish Birding News 1: 62-67

McGeehan, A. 2002. Total Birding. Dutch Birding 24: 304-306.

Svensson, L. 2001. Identification of Western and Eastern Olivaceous, Booted and Sykes's Warblers. Birding World 14: 192-219.

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