The Dorset Yellow Bittern - British Birds

A paper from the British Ornithologists’ Union Records Committee

The Dorset Yellow Bittern

Ian Lewington

Tim Melling, Robert Y. McGowan and Ian Lewington

ABSTRACT A juvenile Yellow Bittern Ixobrychus sinensis was found freshly dead at Radipole Lake, Dorset, on 23rd November 1962. At the time, the bird was dismissed as being a likely escape from captivity, but subsequent information on the potential for long-distance vagrancy in this and other small herons led to the record being assessed by BBRC and BOURC.The identification as Yellow Bittern was accepted by both committees but, as a result of anomalies with the bird’s plumage and the rather unusual circumstances of its discovery, BOURC rejected the record as a first for Britain. n 23rd November 1962, at Radipole Lake, near Weymouth, Dorset, two local birdwatchers were approaching the concrete bridge when a small heron flew across the path some 50 m ahead of them. When they reached the spot where the bird had disappeared from view, they found it, lying dead, at the base of a concrete block, with blood dripping from its bill. They described it as being ‘in the pink of perfection’ when they found it. The initial reaction of the observers was that it was an immature Little Bittern Ixobrychus minutus, and they skinned and dried the corpse without delay. However, subsequent consultation of The Handbook (Witherby et al. 1938–1941) led the finders to doubt the identification. A

O

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week later, on 30th November 1962, they took the bird to the Dorset County Museum, where it was suggested that they send the skin to Dr John Ash, a member of the Rare Birds Committee of the Dorset Natural History and Archaeological Society (DNH&AS), to confirm the identification. According to the finders, the bird was folded into a box before being posted to John Ash, as the skin had been prepared with wings spread, and would have been particularly cumbersome to post without folding. John Ash showed the specimen to members of the DNH&AS Rare Birds Committee, who noted that it showed a few features that were wrong for Little Bittern. Since none of them had sufficient literature or reference material on 137


other Ixobrychus herons, the bird was sent (on 17th January 1963) to the then British Museum (Natural History) (BMNH) in London. There, Derek Goodwin examined the specimen and confirmed its identification as an immature Yellow Bittern I. sinensis. He noted that it differed from immature Little Bittern in that: the top of the head was streaked rather than scalloped; the underparts were more streaked; the coloration was generally more buffy; the wing was much shorter; and the bill was longer. On 28th January 1963, the specimen was returned by Ian Galbraith, Head of the Bird Department at the BMNH, who commented that the bird must have escaped from an aviary, but also noted that Yellow Bittern was not a species commonly kept in captivity. John Ash then contacted D. D. Harber, the BBRC Hon. Secretary. After consultation with

BBRC Chairman P. A. D. Hollom, Harber replied, saying: ‘No, we do not feel that Yellow Bittern can concern us, many thanks all the same. But it makes one wonder what species are kept in captivity – I certainly should not have expected anyone to want to keep this bird.’

Reasons for a review

Peter Coe

Peter Coe

After being dismissed by BBRC in early 1963, the record was largely forgotten about. The only contemporary documentation of the bird was a mention in the proceedings of the DNH&AS (Vol. 84: 63). In 1997, however, the record was included by Morrison (1997), who put forward a case for it being a genuine vagrant; he suggested that an escape from captivity or a shipassisted passage were both unlikely possibilities. In 2002, then-BOURC member Grahame Walbridge suggested that the record should be revisited in the light of what we now know about the vagrancy potential of small herons. Specifically, a propensity for long-distance vagrancy was apparent among a number of similar species (e.g. Striated Butorides striata and Green-backed Heron B. virescens, as well as Yellow Bittern itself (see below), while two Western Palearctic records of Schrenck’s Bittern I. eurhythmus preceded the Dorset Yellow Bittern). Another reason for a review was the lack of any evidence that Yellow Bitterns were kept in captivity at the time of the record. Yellow Bitterns are certainly not commonly kept in captivity, nor have they been in the recent past (Roger Wilkinson pers. comm.). Enquiries in 2002 revealed just two birds, both in collections in southeast Asia, although this was not an exhaustive search of private collections. It is difficult to ascertain captive status retrospectively, particularly as far back as 1962. However, the Zoological Society of London, renowned for keeping unusual species, could find no records of this species in their collections at Regent’s Park Zoo. It seems, therefore, that Yellow Bittern is a gen82 & 83. The Dorset Yellow Bittern Ixobrychus sinensis.

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uinely unlikely species to be kept in captivity. Grahame Walbridge eventually managed to track down the specimen, which had been retained by John Ash and stored in his attic for almost 40 years (plates 82 & 83); the specimen has now been deposited at the Natural History Museum (NHM), Tring, specimen reference number 2003.1.1. When handing over the specimen, Ash commented: ‘Soon after [the original report], I heard that the finder had recently returned from the Far East, as a result of which I considered the circumstances were too suspicious and that the record could not be taken seriously.’ There is no mention of this information in any of the contemporary correspondence, nor was it revealed in the comments of the two circulations of the DNH&AS Rare Birds Committee. Unfortunately, the two original observers could not be traced, although they were known at the time to be members of the DNH&AS.

Distribution and vagrancy Yellow Bittern has a widespread distribution which encompasses much of east and southeast Asia. Its breeding range extends from the Indus Valley in Pakistan and east throughout the lowlands of the Indian subcontinent south to Sri Lanka, and through most of southern and eastern China north to central Heilongjiang province. It has been recorded from Sakhalin and the Kuril Islands in the Sea of Okhotsk, eastern Russia, but breeding has not yet been proven here. In Japan, it is a rare breeding bird on Hokkaido but common throughout the south and into Taiwan. To the south it breeds commonly throughout southeast Asia including the Philippines and Indonesia, and east to New Guinea and New Britain. It has also colonised the Seychelles and has recently bred in Oman. Birds in the southern part of the range are largely resident, but those breeding in much of China and Japan join resident birds in southeast Asia in winter. A few, however, remain in southern Japan throughout the winter (Hancock & Kushlan 1984) and the species is fairly common in Taiwan in winter. Returning migrants reach Hong Kong, Guangdong province, from the last week in March, but first arrivals don’t reach Beidaihe, Hebei province, until mid May and peak towards the end of the month. Return passage through China is less conspicuous as migrants and local breeding birds occur together, but birds are still passing through Hong Kong until the last week in British Birds 101 • March 2008 • 137–141

October and perhaps until the end of November (Carey et al. 2001). The species is monotypic and there is no evidence that migratory northern birds tend to have longer wings, as might be expected. There have been several records of vagrant Yellow Bitterns occurring well outside their usual range. There is one fully documented record of a vagrant reaching Western Australia (in 1967), plus a further two, inadequately documented and old records for Australia (Davies et al. 1991). There are also two records from Christmas Island, which lies 500 km south of Java in the Indian Ocean (1978 and 1985) (Davies et al. 1991). A record in 1989 from Attu Island, in the Aleutian archipelago, Alaska, confirmed susceptibility to vagrancy well beyond the bird’s normal range (Gibson & Kessel 1992). To the southwest of its Asian range, it has been reported from the Maldives (Rasmussen & Anderton 2005) and is a rare resident in the Seychelles, where there is a small breeding population. It has recently colonised Oman, where it was first recorded in 1984, but by 2003 there had been 59 records, with a maximum count of six individuals. Breeding in Oman was confirmed in 2002 (Eriksen et al. 2003). There is also one record, in 1999, from the island of Socotra, Yemen, which lies off the Horn of Africa (Aspinall et al. 2004). Although extremely unlikely, it is therefore not impossible that a vagrant Yellow Bittern could reach Britain.

The BOURC review Examination of the skin of the Dorset Yellow Bittern, and comparison with other reference skins at the BMNH and the National Museums of Scotland, revealed that the bird had been in juvenile plumage when it had died and had not yet started a post-juvenile moult. There is little published information on moult in Yellow Bittern, or indeed in other members of the genus Ixobrychus. Little Bittern does not begin post-juvenile moult until reaching its winter quarters, whereas Schrenck’s Bittern undergoes post-juvenile moult prior to autumn migration. However, the most unusual aspect of the Dorset Yellow Bittern was the particularly dark pigmentation of its flight feathers (plate 84). Comparisons were made with 73 other juvenile Yellow Bittern skins in the NHM, Tring, and the pigmentation of the remiges of the Dorset bird was significantly darker than on virtually all of them. Only one other bird came close to matching the 139


Another anomaly was the width and shape of the flight feathers. The Dorset specimen had strikingly broad, squareended primaries whereas all the other 116 Yellow Bittern skins examined at the NHM, Tring, had narrower flight feathers with more pointed tips (plate 84). The widths of the primaries of the Radipole bird were approximately 20% broader than those of other Yellow Bitterns examined (plate 85). This apparently 84. Comparison of primary pigmentation of the Dorset Yellow Bittern atypical feather growth is difIxobrychus sinensis with that of another juvenile Yellow Bittern from the ficult to explain but is clearly Natural History Museum,Tring. not due to feather wear; the remiges of many of the other juvenile Yellow Bitterns examined were in pristine condition, just like those of the Radipole bird. A third unusual feature of the specimen was the method of preparation. Preparation of a bird skin normally involves removal of just the muscles and tendons along the radius and ulna Mid-primary width of (the bones that support the mid-wing). Both adult male Yellow Bittern the radius and the ulna had been removed entirely from both wings of the Dorset bird, however, leaving no insertions for the secondaries. The finders also mentioned that they had skinned and dried the bird before taking it to the Dorset County Museum, just seven days after finding it. The bird was prepared as a flat skin, rather than as a standard ‘filled’ cabinet skin. The appearance was almost as if the skin had been flattened by a large flower press, to Mid-primary width of little advantage other than that it could be Dorset Yellow Bittern stored in a confined space. The finders had few skills in preparing bird skins, admitting to ‘skin85. Comparison of the primary widths of the ning and drying it (not very well at that)’. It Dorset Yellow Bittern Ixobrychus sinensis and seems curious that they attempted this themanother juvenile Yellow Bittern from the selves, rather than take the fresh specimen Natural History Museum,Tring. straight to Dorset County Museum, especially colour, an individual collected in June, presumsince they thought it was a Little Bittern (or ably soon after it fledged. The only reasonable possibly something rarer) and therefore someexplanation for the flight feathers of the Dorset thing that would be of particular interest to the bird being so dark is that it had had little expomuseum. They also indicated that they had no sure to sunlight after fledging – for example, if it desire to keep the specimen, which also seems at had died while its plumage was very fresh or it odds with their efforts to skin and prepare the had been kept in captivity, away from sunlight. bird before taking it to the museum. Certainly, the plumage condition was not conIn addition to the above points relating to the sistent with that of a wild bird, exposed to specimen, there are several elements regarding natural light for several months and a journey the finders and the circumstances surrounding from east Asia to Britain. the discovery which caused the reviewers

Ian Lewington, © NHM,Tring

Ian Lewington, © NHM,Tring

Dorset Yellow Bittern

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Juvenile Yellow Bittern in November

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concern. The observers claimed that the bird was found dead ‘at the base of a concrete block’. There are no concrete blocks at Radipole Lake but the concrete bridge still exists (plate 86). Many birds collide with wires and windows, which may be difficult to see in certain conditions, but they rarely collide with highly visible solid objects. Yet the bill is in pristine condition with no scratches or chips. Death through such a collision seems highly unlikely, and the condi86. The concrete bridge at Radipole Lake where the Dorset tion of the bill is inconsistent Yellow Bittern Ixobrychus sinensis was reportedly found. with this hypothesis. Roger Wilkinson. Particular thanks are due to Grahame On finding a dead rarity, most birdwatchers Walbridge for tracking down the specimen and researching would surely have taken the entire corpse to the its history. We also thank BBRC for their review of the museum; the option of preparing the skin indeidentification, par ticularly Brian Small, who provided pendently seems particularly odd given that the detailed measurements and photographs of the specimen. In addition: John Ash provided the actual specimen, plus finders had few taxidermy skills. If they had extremely useful comments on the record; Peter Coe expected a long delay before the bird was allowed us to use his images of both the Radipole received by the museum, they might have prespecimen and live Yellow Bitterns; Katrina Cook (NHM, Tring) arranged access to the collections at Tring; Steve pared it themselves to preserve the specimen, Dudley commented on early drafts of this article; Peter but they took it to the museum just seven days Summers provided expert comment on skin preparation after finding it. The report that one of the techniques; and Roger Wilkinson gave help and information finders had returned recently from the Far East on the current and former captive status of Yellow Bittern. is also, in the context of other anomalies, sugReferences gestive. It is extremely difficult to assess a record Aspinall, S. J., Porter R. F., & Al-Saghier, O. 2004. Four new such as this, when efforts to trace the original bird species in Yemen from Socotra. Sandgrouse 26: observers have failed and it was not possible to 48–50. corroborate any of the facts. Nevertheless, the British Ornithologists’ Union (BOU). 2006. Records Committee: 33rd Report (April 2006). Ibis 148: 594. reported circumstances surrounding this record Carey, G. J., Chalmers, M. L., Diskin, D. A., Kennerley, P. R., are certainly unusual, perhaps even suspicious. Leader, P. J., Leven, M. R., Lewthwaite, R.W., Melville, D. S., BBRC assessed this record in 2003 and they Turnbull, M., & Young, L. 2001. The Avifauna of Hong Kong. confirmed the identification as a juvenile Yellow Hong Kong Bird Watching Society, Hong Kong. Davies, J. N., Marchant, S., & Higgins, P. J. (eds.) 1991. Bittern. They also commented upon the anomHandbook of Australian, New Zealand and Antarctic Birds. alous shape and coloration of the flight Vol. 1: Ratites to Ducks. OUP, Melbourne. feathers, while the reported circumstances of Eriksen, J., Sargeant, D. E., & Victor, R. 2003. Oman Bird List. the record raised many questions. The record 6th edn. Centre of Environmental Studies and Research, SQU, Oman. was subsequently assessed by BOURC, who also Gibson, D. D., & Kessel, B. 1992. Seventy-four new avian accepted the identification, but it was not taxa documented in Alaska 1976–1991. Condor 94: accepted onto the British List because of the 454–467. Hancock, J. A., & Kushlan, J. A. 1984. The Herons Handbook. doubts surrounding the record described above Croom Helm, London. (BOU 2006). Acknowledgments We are grateful to all members of BOURC, past and present, who have commented on this record and on drafts of this ar ticle: Colin Bradshaw, Mar tin Collinson, Andrew Harrop, Chris Kehoe, Andrew Lassey, Eric Meek, Richard Millington, Steve Votier, Grahame Walbridge and

Morrison, S. G. 1997. Rare Birds in Dorset. Privately published, Dorset. Rasmussen, P. C., & Anderton, J. C. 2005. Birds of South Asia. The Ripley Guide.Vol. 2. Smithsonian Institution and Lynx Edicions,Washington, DC and Barcelona. Witherby, H. F., Jourdain, F. C. R.,Ticehurst, N. F., & Tucker, B.W. 1938–1941. The Handbook of British Birds. Witherby, London.

Tim Melling, Robert Y. McGowan and Ian Lewington, c/o RSPB, Westleigh Mews, Wakefield Road, Denby Dale, West Yorkshire HD8 8QD British Birds 101 • March 2008 • 137–141

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Peter Coe
