The identification of a hybrid Canvasback Common Pochard: implications for the identification of vagrant Canvasbacks Keith Vinicombe 74. Adult male hybrid Canvasback Aythya valisineria Common Pochard A. ferina, Chew Valley Lake, Somerset, June 2002. Although vertical in the photograph, it sometimes showed a sloping line of demarcation between the dark breast and the pale flanks, like Canvasback. Note that it is starting to moult into eclipse plumage and is losing the white marks on the bill (see text). P. Burrows ABSTRACT The identification of a male hybrid Canvasback Aythya valisineria Common Pochard A. ferina at Chew Valley Lake, Somerset, is discussed. The most important character for separating a pure-bred Canvasback from a similar hybrid or impure individual is the presence of small white marks on the bill. The identification of Canvasback in Europe requires caution. Critical examination of all the key features, both structural and relating to plumage, is essential, and particular attention should be paid to the bill. 112 British Birds 96 March 2003 112-118
On 21st March 1993, I discovered an unusual adult Aythya duck feeding off Moreton Bank, Chew Valley Lake, Somerset (plate 74). It closely resembled a male Canvasback A. valisineria, but the mantle, scapulars, wings and flanks didn t appear to be quite white enough and its forehead was not as dark as I would have expected. Furthermore, when viewed in profile, the head-and-bill shape was not sufficiently attenuated and the neck was not quite long enough. More significantly, it showed a small, pure white, kidney-shaped patch just before the tip of an otherwise black bill. In addition, what appeared to be a small white scratch mark was visible on the right side of the bill, closer to the tip than to the base. The bird did, however, show many features consistent with male Canvasback, including a noticeably brighter red eye than male Common Pochard A. ferina, a darker chestnut head and, in profile, two bulging ridges at the base of the upper mandible and a sloping line of demarcation between the black breast and pale flanks. Unlike Common Pochard, it often jumped high out of the water when diving. I saw it on a further three occasions up to 25th April 1993 and I confidently identified it as a hybrid Canvasback Common Pochard. Hybrid or the real thing? Following its appearance in 1993, the duck was not seen in 1994 but, to my surprise, it reappeared between 19th and 31st March 1995, although it was peculiarly elusive. A slight unease about the identification was brought into focus by two further developments. Firstly, during a visit to the Wildfowl and Wetlands Trust (WWT) at Slimbridge, Gloucestershire, on 19th March 1995, I watched several male Canvasbacks in the collection and was surprised to discover that about half showed small white marks near the tip of the bill, similar to those shown by the Chew bird. Subsequently, John Martin showed me photographs of a captive male Canvasback at Bristol Zoo which showed even more extensive white bill markings (plate 75). Secondly, on 25th January 1997, I saw Britain s first accepted wild Canvasback, a firstwinter male at Wissington, Norfolk (although a previous record from Cliffe, Kent, in December J. P. Martin 75. Captive adult male Canvasback Aythya valisineria, Bristol Zoo, winter, mid 1990s. Given the amount of bluish-white on the bill, this is perhaps a first-generation hybrid Canvasback Common Pochard A. ferina but otherwise it closely resembles a Canvasback. British Birds 96 March 2003 112-118 113
76. Captive first-winter male Aythya duck, thought to be a hybrid Canvasback A. valisineria Common Pochard A. ferina, Wildfowl and Wetlands Trust, Slimbridge, Gloucestershire, February 1997. Although superficially resembling a Canvasback, its structure is not completely convincing for that species and it shows a small white subterminal patch on the bill. Note that both first-winter Canvasback and Common Pochard can be easily aged by their darker grey wing-coverts, which in adults are pale grey and concolorous with the flanks and scapulars. 1996, has since been accepted as the first) (BOURC 2003). I was surprised at just how similar to accompanying Common Pochards the Norfolk bird could look, particularly in dull light and/or when asleep. In certain lights, it did not look as large, as pale or as attenuated as some literature suggests. Inevitably, these experiences set me thinking about the Chew bird. Rather than being a hybrid, could it have been a pure Canvasback with white on the bill? To counter these thoughts, in February 1997 I was shown four first-winter Aythya ducks in the holding pens at WWT Slimbridge which were thought to be hybrids between a captive Canvasback and a wild Common Pochard (plates 76 & 77). There was no denying that these birds showed some similarities to the Chew bird. In an attempt to take the matter further, I wrote to the editors of Birding, the magazine of the American Birding Association, enquiring whether North American birders had ever 77. Captive first-winter female Aythya duck, thought to be a hybrid Canvasback A. valisineria Common Pochard A. ferina, Wildfowl and Wetlands Trust, Slimbridge, Gloucestershire, February 1997. Unlike its male sibling in plate 76, this bird completely lacks white bill markings, but its structure seems intermediate between Canvasback and Common Pochard. Such an individual would be very difficult to identify with certainty in the field. encountered male Canvasbacks with white markings on the bill. Two photographs appeared in Birding (Vinicombe 1998): one of a bird at WWT Slimbridge and the other of the Bristol Zoo bird (see above). An expert comment from Richard Ryan (Ryan 1998) suggested that they were probably both Canvasbacks rather than hybrids, but that such individuals were most likely to occur in captivity as a consequence of either (a) inbreeding in a small captive population (the species is apparently difficult to breed in captivity), or (b) damage to the bill. One of the markings on the bill of the Chew bird, and some of those shown by the birds at WWT Slimbridge, indeed resembled scratch marks and this made the latter theory seem particularly plausible. Despite these comments, however, I could not prove that the Chew bird was a Canvasback, particularly given the lack of confirmation from North America that such individuals exist in the wild. Despite these helpful comments, the identity of 114 British Birds 96 March 2003 112-118
our bird seemed doomed to uncertainty unless it reappeared again. Although it was not seen in 1996 and 1997, the Chew bird did return in April 1998 and on 14th May I enjoyed particularly good views of it displaying to Common Pochards. As a consequence of these views and the comments from Richard Ryan, I became more convinced that it was indeed a Canvasback, rather than a hybrid. This view was reinforced by two behavioural observations: (1) when displaying, it inflated its throat, which then appeared rather like a small ball at the base of the lower mandible; and (2) it persistently and vigorously threw back its head in the manner of a displaying Ring-necked Duck A. collaris. Although Common Pochards occasionally display in this fashion, they do not do so habitually or as frequently. The Chew bird was present again in April 1999, when it remained elusive, but it was not seen in 2000. In August 2000, I visited Bristol Zoo and found that all the male Canvasbacks there (about six) showed small white marks on the bill. The evidence to suggest that Canvasbacks could indeed show such markings seemed to be mounting. In April 2001, the Chew bird reappeared yet again, but, to everybody s amazement, it suddenly took to feeding on bread provided by human visitors. Although wild birds may come to bread, it had to be conceded that this development was suspicious. On 9th May, I decided to test its tameness. I approached the lake through a small wood at the edge of Herons Green Bay, well away from the usual feeding spot by the road, armed with a loaf of bread. While all the Common Pochards, Tufted Ducks A. fuligula and Common Coots Fulica atra swam away at my approach, the Canvasback swam straight towards me, approached to within 10-15 m and readily accepted the bread that I threw at it! Regardless of its identity, it seemed clear that it was an escape from captivity. It was present during May-June 2002, but it had by then reverted to its previously elusive behaviour. Hybrid Canvasback Common Pochard Origin of the Chew bird Amazingly, there was to be a final twist to the story. In July 2001, I received a letter from Phil Bristow informing me that at Roath Park Lake, Cardiff, South Glamorgan, a pinioned female Canvasback bred with a wild male Common Pochard in both 1990 and 1991 and produced hybrid young. In 1990, she hatched seven young, six of which fledged, while in 1991 she produced six young, but it is not known how many survived. Plate 78 shows two of the juvenile hybrids from the 1990 brood. Although I was vaguely aware of these records and subsequently discovered that details had been published (Bristow 1992), I did not connect them with the Chew sightings. PB also sent me some slides of a surviving male hybrid in adult plumage, taken in March 1997. It was undoubtedly our bird! It had exactly the same pattern of white on the bill as well as the same overall appearance (plates 79-80). Moreover, PB furnished me with a long series of dates between 1997 and 2001 when the bird was present at Roath Park Lake. None of these dates overlapped with its appearances at Chew. It was clear, therefore, that it had been commuting back and forth across the Bristol Channel, a distance of some 30 km. 78. Two juvenile Canvasback Aythya valisineria Common Pochard A. ferina hybrids, Roath Park Lake, Cardiff, South Glamorgan, July 1990. Note the long, attenuated bill, the sloping forehead and long neck, all typical of Canvasback. P. Bristow British Birds 96 March 2003 112-118 115
80. Adult male hybrid Canvasback Aythya valisineria Common Pochard A. ferina, Roath Park Lake, Cardiff, South Glamorgan, March 1997.The same bird as that in plates 74 & 79.This photograph shows how long and thin the neck could appear. Also note the relatively brown forehead compared with a pure Canvasback. P. Bristow P. Bristow 79. Adult male hybrid Canvasback Aythya valisineria Common Pochard A. ferina, Roath Park Lake, Cardiff, South Glamorgan, March 1997, with adult male Common Pochard behind.this individual superficially resembles a Canvasback but note the white kidney-shaped patch on the bill, although this appears whiter and more prominent in the photograph than it normally did in the field. It is considered to have been the same bird as that recorded at Chew Valley Lake, Somerset, intermittently from 1993 to at least 2002 (plate 74). Identification repercussions The identification of the Chew bird has significant repercussions for the identification of Canvasback in Britain. Firstly, it is clear that Canvasback Common Pochard hybrids can appear very similar to pure Canvasbacks, both in plumage and structure. Secondly, from my experiences at both WWT Slimbridge and Bristol Zoo, I would suggest that a significant number of captive Canvasbacks in Britain are either inbred or polluted with Common Pochard genes. While most captive Canvasbacks are clearly not first-generation hybrids, it seems likely that many share their ancestry with Common Pochards. Whether all captive Canvasbacks in Britain are tainted in this way is not known. The most important difference between a Canvasback and a hybrid, or an inbred or impure captive bird, is the presence of small white marks on the bill. At present, there is no evidence to suggest that wild Canvasbacks ever show such marks. Any suspected vagrant Canvasback found in Europe should, therefore, be examined very carefully for such markings, and any individual which shows white on the bill should not be identified as a Canvasback nor accepted as such. It must be stressed that on some of the birds at WWT Slimbridge, these marks were so tiny that they were visible only at close range (plates 81 & 82 show two of the Slimbridge males, the bird in plate 82 having particularly subtle bill markings). In my opinion, it is essential that descriptions of male Canvasbacks submitted to national records committees contain confirmation that the bill was examined critically at close range, and that white markings were specifically and carefully looked for and were not present. The problem of eclipse males, females and juveniles While adult males in full plumage should be identifiable, the problems presented by inbred or impure eclipse males, females and juveniles are imponderable. Any white bill markings are likely to be reduced or even absent in eclipse, thereby making the identification of adult males in late summer much more difficult (see plate 83). Indeed, the Chew bird was losing its 116 British Birds 96 March 2003 112-118
81. Captive adult male Canvasback Aythya valisineria, Wildfowl and Wetlands Trust, Slimbridge, Gloucestershire, March 2002. With the exception of a small white subterminal patch on the bill, this bird showed all the characters of a pure Canvasback.The classic characters of Canvasback, compared with Common Pochard A. ferina, comprise a relatively long neck, a higher-based and longer, all-black bill which bulges at the base and merges with a distinctively high, peaked crown. In terms of plumage, adult males have the mid-body whitish-grey, paler than on Common Pochard, while the boundary between the black breast and the pale flanks is often distinctly forward-sloping (almost vertical in Common Pochard). Additionally, the forehead area is distinctly blackish in Canvasback. bill markings towards the end of its stay in both June 2001 and June 2002, as it moulted into eclipse plumage (see plate 74). It is interesting to note that, while two first-winter males in the brood of four apparent hybrids at WWT Slimbridge in February 1997 showed white bill markings, their two female siblings did not (see plates 76 & 77). When identifying eclipse males, females and juveniles, it seems clear that no plumage characters exist which would separate an inbred or impure Canvasback from the real thing. Very careful attention must be paid to structure, although only a first-generation hybrid would be likely to lack the more extreme proportions shown by a pure Canvasback. 82. Captive adult male Canvasback Aythya valisineria, Wildfowl and Wetlands Trust, Slimbridge, Gloucestershire, March 1995.This individual appeared to be a Canvasback, except that it showed tiny white subterminal marks on the bill, suggesting that it was either inbred or that its lineage was not pure. It seems that many captive Canvasbacks in Britain show such markings, which would be extremely difficult to see in the field. British Birds 96 March 2003 112-118 117
Conclusions The identification of Canvasback in Europe requires the utmost caution. It must be clearly established that a suspected individual has a completely black bill and shows classic Canvasback plumage and structure, particularly the long, thin looking bill (see plate 81). Photographic evidence to support both the identification and the adjudication of such records is highly desirable. In my opinion, the only way that records committees can deal with the problem is to continue to accept only those individuals which show the full suite of classic characters, with the proviso that escaped inbred or impure individuals could occasionally slip through the net. To assess the likelihood of this, those committees will also need to make a full and objective assessment of the escape potential of any apparent vagrant. Although these findings could be used to cast aspersions on the four accepted British records of Canvasback, two of those were supported by photographs. The fact that both photographed individuals lacked any traces of white on the bill and appeared to be perfect Canvasbacks in both plumage and structure suggests that (a) they were probably pure bred, and (b) they did not have a captive origin. It should also be stressed that all the captive Canvasbacks that I studied were pinioned. Acknowledgments I am very grateful to Phil Bristow for supplying the solution to the identification of the Chew bird and for providing me with his notes and photographs. I am also grateful to John Robinthwaite for showing me around some of the non-public pens at WWT Slimbridge, and to P. Burrows and Ian Stapp for video footage and photographs of the Chew bird. References BOURC. 2003. British Ornithologists Union Records Committee: 29th Report (October 2002). Ibis 145: 178-183. Bristow, P. 1992. Pochard Canvasback hybrids in Britain. Birding World 4: 437. Ryan, R. 1998. Scuffing yes, but probably not Contamination. Birding 30: 61-62. Vinicombe, K. 1998. Strange Aythya Ducks: can Canvasbacks show white on the bill? Birding 30: 60-61. Keith Vinicombe Bristol 83. Captive eclipse male Canvasback Aythya valisineria, Wildfowl and Wetlands Trust, Slimbridge, Gloucestershire, July 1999.This bird resembles a pure Canvasback but it is likely that any white on the bill may be reduced or even lost in eclipse, perhaps making definitive identification impossible. What is interesting about this bird, however, is that its head is far more female-like than that of a male Common Pochard A. ferina in eclipse, but it can of course be readily sexed by its red eye colour. In contrast, eclipse plumage of male Common Pochard resembles dulled-down breeding plumage. 118 British Birds 96 March 2003 112-118