| .Jason Crook's Birding Local A HYBRID BLACK BRANT? |
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For the fifth consecutive winter a Brent Goose Branta bernicla showing characteristics of the North American and East Siberian race B. b. nigricans - colloquially known as the Black Brant - has returned to the North Hayling Oysterbeds / South Moor shore area of Langstone Harbour, Hampshire. In each year that the bird has returned it has increasingly resembled a Black Brant, to the extent that in its present plumage it looks much like many of the vagrant Black Brants currently being identified in Britain. However, having found the bird in February 1998 and made extensive observations of it throughout the periods it has spent in Langstone Harbour since then, I have remained of the opinion that the bird is likely to be a hybrid / intergrade between Dark-bellied Brent Goose B. b. bernicla and Black Brant. Notwithstanding this, the fact that the bird has exhibited such age-related changes to its plumage may be of interest for those observers finding and/or identifying vagrant Black Brants in North-western Europe or elsewhere. The documentation of this bird forms the core of the rest of this article. The following is an account and description of the bird which I submitted to the British Birds Rarities Committee in spring 2000 (after the third winter it had spent in Langstone Harbour). With this description I also submitted a full description of an adult Black Brant I had found at Farlington Marshes Wildlife Reserve on November 13th 1999. This bird was seen by many observers virtually daily until February 18th 2000. Some of my notes compare this bird, which was unequivocally accepted as a Black Brant by all those birders who saw it, with the Hayling Oysterbeds goose. Photographs of both birds were also submitted. They were taken by Kevin Crisp and two of them, showing each of the two birds, can be found in the 1999 Hampshire Bird Report (published by the Hampshire Ornithological Society). Alternatively, the picture of the Oysterbeds goose can be viewed by clicking here. It should be noted that my use of the single terms �hybrid� and �intergrade� are wholly transferable, as I have chosen not to enter into the debate on whether the various, distinct forms of Brent Geese are separate species or just races [notes or comments added later are in blue type]. BRENT GOOSE Branta bernicla showing characteristics of race B. b. nigricans (Black Brant) LOCALITY : NORTH HAYLING OYSTERBEDS AND SOUTH MOOR SHORE, LANGSTONE HARBOUR, DATES: 12 November 1999 - 13 March 2000 PREVIOUS EXPERIENCE : A Black Brant was seen at West Wittering, West Sussex, in February 1999. CURRENT EXPERIENCE : Almost daily observations of a Black Brant at Farlington Marshes Wildlife EXPERIENCE OF BRENT GEESE: Very familiar with the Dark-bellied race of Brent Goose Branta bernicla bernicla (including the many variations of the typical plumage type) and reasonably familiar wiith the Pale-bellied race B. b. hrota (several singles and once a group of three with wintering flocks of bernicla and recently (autumn 1999) a flock of 33 (presumed) Canadian/Greenland-bred birds on passage), all in the Langstone Harbour area. [In the last two winters increasing numbers of Pale-bellied Brent have over-wintered with the flocks of Dark-bellied Brent in Langstone Harbour, with 7 in 2000-01 and up to 9 during this winter.] Background to observations During February and March of both 1998 and 1999 a very distinctive adult Brent Goose Branta bernicla was present in the North Hayling Oysterbeds and South Moor shore area of Langstone Harbour. It showed many of the plumage features associated with Black Brant B. b. nigricans. In early 1998 it was paired with a bird showing plumage features half-way between it and the Dark-bellied Brent Geese B. b. bernicla present (in fact, to my eyes, it looked like a variation on the typical bernicla plumage rather than something �different�). In early 1999 it was paired with a different bird, one showing typical bernicla features. In this winter the pro-nigricans features were stronger, but still not �full-on�, and no matter how long I looked at it I still couldn�t make a firm decision. At this time I also went to see a Black Brant that had been wintering at West Wittering, Chichester Harbour, in Sussex. I saw it twice over a five week period. This was my first encounter with nigricans. My opinion of the Oysterbeds bird changed little. Whereas in both the previous two winters I had not searched through the geese before mid-winter and therefor did not see the bird until February, a conscious effort was made at the beginning of the 1999/2000 winter to locate the bird when it first arrived. Frequent visits during the autumn finally paid off when I located the bird, with its �normal� partner, on 12 November 1999, but the views were both distant and brief before it flew off. I was happy that it had arrived fairly recently. The very next day I had the good fortune to find a Black Brant at Farlington Marshes. With the Oysterbeds bird still nagging at the back of my mind, two days later I was back looking at it in good light and at close range feeding along the foreshore near Langstone Bridge. I was not altogether surprised that it now looked like a fairly good, but small, Black Brant, but still lacking some of the intensity of contrast in plumage tones that the Farlington bird (and the Sussex bird of the year before) showed. DESCRIPTION As part of my note-taking process in late November 1999 I tried to describe the plumage differences between the Black Brant at Farlington Marshes and the bird at Hayling Oysterbeds. A direct comparison between the two individuals was not possible, as they frequented different areas of Langstone Harbour. However, detailed observation of both birds combined with a comparison of each with accompanying bernicla made an indirect comparison possible. A summary of these notes is as follows: �Three main plumage differences are apparent. Firstly, the Farlington bird is slightly darker on the belly and breast sides, with the Oysterbeds individual showing more contrast between the black neck �sock� and these areas. (It is important to note that the Oysterbeds bird is still obviously darker on the belly and breast sides than bernicla.) Secondly, the white flanks of the Farlington bird are larger. The white feathering extends to the thighs and forms broader triangular �segment�-shaped patches, compared to the more rectangular patches along the flanks of the Oysterbeds bird (the right-side flank patch in particular being truncated above the thigh). Thirdly, the white neck patches are different. On the Farlington bird the join of the collar at the front of the neck is made up of several ribbons, while the �spiders web� is more broken and less significant than that on the Oysterbeds bird, which in comparison is more strongly webbed. The collar on the Oysterbeds bird is also more solidly joined at the front of the neck. One of the effects of these differences is that it is possible to pick out the Oysterbeds individual by its neck patch alone (not that this is ever necessary), whereas the Farlington bird is not confidently identified by this feature, with usually several accompanying bernicla having equally extensive neck patches in side view.� This last statement was true at the time, but by late December the Black Brant at Farlington did begin to show a much broader neck collar. The relative proportions of the bird was more-or-less the same as the other Brent present, although it did often look rather small-headed, but this can probably be attributed to its overall small size. Its shape always looked box-like to me. By this I mean that the various planes of its body were fairly flat and the �joins� between them rather angular. This was in contrast to the Black Brant at Farlington, which looked rather lumpy and rounded in shape in comparison. No difference to the shape or structure of the bill of the Oysterbeds bird (in comparison with Dark-bellied Brent) was ever noticed. By late December several subtle changes to the plumage of the Oysterbeds bird had taken place, leaving it looking much more like it had appeared the previous winter. By February it looked more-or-less the same as it had done a year earlier. The differences between how it looked in November 1999 and February 2000 can be summarised as follows: The contrast between the neck �sock� and the rest of the body was slightly more marked, especially the demarcation between the brown-black lower breast and the black neck �sock�. This was attributed to a slightly lighter browner black colour to the underparts. The sides of the body (the area between the neck �sock� and the fore-flanks) had become even more obviously lighter and browner in tone, which had the effect of highlighting any contrast the rest of the body had with the neck �sock�. The white rear flanks, although they covered the same area, had become less intense, especially on the left side. This was because the white edgings to some of these feathers had become partly worn off, leaving more of the dark base colour to show through as rather blotchy patches, rather than the thin crescents it previously showed. These changes did not surprise me, as my own observations of bernicla show that they are still moulting some of their body feathers when they arrive back in Langstone Harbour in the autumn and continue to do so for some weeks. The broadening of the neck collar on the Black Brant at Farlington could easily be attributed to this as well. Also, other feather tracts that they have usually moulted earlier in the autumn (such as their flight feathers and wing coverts) become more worn by the end of the winter and this can effect their apparent colour and tone. Certainly bernicla typically look to have greyer upperparts by spring, with a certain brown �glaze� to their underparts. I must stress that the overall change in the appearance of the Oysterbeds bird was a combination of the several subtle changes to its plumage detailed above, and really was a case of �the sum total being greater than the parts�. [I have subsequently described the bird as being a Brent Goose with some Black Brant plumage features �painted on�, but nothing more than this. Although this is very simplistic, it does highlight one of my concerns that, even if it was a poorly-marked Black Brant that has improved with age, should it not be more than this? Certainly the other Black Brants I have seen, as well as having unquestionable plumage features of that form, have also had a rather different overall jizz to them compared with the accompanying Dark-bellied Brent Geese.] It should be mentioned that I was never sure which sex the bird was. On the basis of size alone it was a female, but it often behaved like a male, being the more dominant and aggressive partner. I am unwilling to take its size as an absolute indication of its sex for the simple reason it was the smallest Brent Goose in this part of the harbour, and probably the smallest adult I have ever seen. The possibility of it being a hybrid/intergrade (see later) may have a bearing on its size, in that other hybrid wildfowl do not necessarily look the same size as the parent species. Behaviour: Similar to the previous two winters the bird (and its partner) frequented the North Hayling Oysterbeds (on the north-west side of Hayling Island) and South Moor shore (between Langstone Bridge and Budds Farm Sewage Treatment Works) area of Langstone Harbour. Its daily routine was the same as many of the other Brent in this sub-population of the harbour. I never observed them feeding on nearby fields of grass or winter cereals on Hayling Island. They seemed to be exclusively algae feeders. During the 3/4 hours of daytime high tides they were invariably to be found at the Oysterbeds, loafing or feeding on and around the bund walls there. During the falling tide they would fly to the shoreline of South Moor, where they would spend time bathing and preening in the freshwater outflow of a local stream, before either feeding along the inter-tidal zone there (often just north-west of Langstone Bridge) or returning to Hayling to spend the low tide around their favoured parts of the bund walls of the Oysterbeds. On just one occasion, in stormy weather, a visit to the site at high tide failed to locate the bird (or, indeed, any Brent), while on another it flew in from the direction of Long Island (to the west) while I watched. On all other visits I always managed to locate the bird, using my knowledge of its tide-related movements and its favoured feeding spots. Discussion So is it a Black Brant or not? My own feelings are mixed. It does show a larger neck collar (joining in the front), darker brown-black upperparts and whiter flanks than bernicla. Its lower breast and belly and body sides, although darker than bernicla, are still not as dark as might be expected on a typical nigricans. Its white flank patch is not particularly large or extensive, and the small size of the bird is also worrying. It could be argued that it is an atypical individual, just showing some individual variation that many species and sub-species show. Certainly bernicla shows quite an extensive range of variation. I have considered the possibility of it being a �Grey-bellied Brent� (the apparently distinct population of Brent breeding on Melville Island, Canada, and wintering in the Puget Sound area along the Pacific coast of the USA - see Garner 1998), but the birds plumage tones are not particularly brown, or the belly noticeably paler in the central belly region. Also, the neck collar is not broken at the front. In addition, this form is perhaps unlikely to occur with wintering flocks of bernicla in south-east England. Zockler, Syroechkovski and Lappo, in their reply to the critique of their previous paper (British Birds 91:565-572) by Sangster (British Birds 93: 94-97), makes mention of the two major features for identifying nigricans - namely the broad white neck collar and the obvious white patch on the flanks (Millington (1997) also citing the darker and browner upperparts and underparts), but no specific mention of the shape and length of neck, or head and bill shape (as Sangster and Millington do). They only perhaps elude to this in their concluding sentence when they write of their �plan to publish detailed information on the cline in morphology to demonstrate fully the extensive variation of Brent Geese throughout Siberia� (italics my own). I look forward to this, as I am still not sure how to assess the features that the Oysterbeds bird shows, or whether any of them (or a combination of them) are diagnostic of nigricans. At present I feel there are two choices. The bird is either a nigricans (showing variation on the typical plumage state) or an example of an intergrade between nigricans and bernicla (or a hybrid). I do not believe it is a bernicla, both because of the pro-nigricans characters it shows, and because I have seen thousands of bernicla wintering on south coast estuaries and none have shown a combination of these features (and indeed, none have shown a flank patch like it has). References : Garner, M. 1998. Brent crosses. Birdwatch December edition: 29-32. Millington, R. 1997. Separation of Black Brant, Dark-bellied Brent Goose and Pale-bellied Brent Goose. Birding World 10: 11-15. Sangster, G. 2000. Taxonomic status of bernicla and nigricans Brent Geese. British Birds 93: 94-96. Syroechkovski, E. E., Zockler, C., & Lappo, E. 1998. Status of Brent Goose in northwest Yakutia, East Siberia. British Birds 91:565-572. Following my submission of these notes the BBRC decided not to accept the record as nigricans. They did accept the Black Brant that had wintered at Farlington Marshes. Although not specifically referring to the bird at Hayling Oysterbeds, the present committee�s opinion on the problem of potential intergrades was summarised in their annual report, Rare birds in Great Britain 2000. They have written �Taxonomic uncertainties and the presence of non-typical birds showing some, but not all, of the features of B. b. nigricans continue to be a problem. One such record in Norfolk in 1998, which was referred to in last year�s report as a bird showing a reduced neck-band, is now considered to be unacceptable (J. Martin, Brit. Birds in prep.). Such birds are difficult to deal with, but, in order to try to establish a degree of consistency, our approach is usually to accept only those individuals showing the full suite of identification features. It is possible that some intermediate-looking birds may, in fact, have a perfect pedigree for nigricans, but BBRC will generally err on the side of caution when dealing with races, such as this, where intergrades are possible.� (British Birds 94:460, October 2001) Since I wrote these notes the bird has returned in a further two winters (up to the present time) and now shows the intensity and contrast of plumage tones of a pure Black Brant. Most obviously in the present winter it�s upperparts, lower breast and belly are all slightly darker still, while the white neck collar is marginally bolder. At the same time it has continued to look more convincing as nigricans in the first part of the winter in the weeks following it�s late-autumn arrival, just like I have described in the above account of it�s appearance in the winter 1999-2000. It is still paired with the same Dark-bellied Brent Goose. During the 2000-2001 winter they were accompanied by two young. Although these looked very like typical bernicla juveniles, they developed increasingly different plumages as the winter progressed. They both had mottled flanks, but one developed much more white along the upper flanks. This bird also had slightly darker upperparts. They both had similar neck collars which were no more obvious than on typical bernicla and did not meet across the front of the neck under the chin. Unfortunately the family were last seen on January 18th 2001, so the full extent of the plumage development of the juveniles through to the end of their first winter was not recorded. With the returning adult now looking like an acceptable Black Brant I feel it would be very easy to conclude that, after previous uncertainty, it is one after all. Instead, it�s return has made me consider still further the real identification of this bird, and, in particular, to consider one of the remaining questions: Can a pure Black Brant change so much that in it�s earlier years it was not acceptable as such? Before this question can be seriously answered the possibility of it being a hybrid or intergrade between bernicla and nigricans should be considered. It certainly meets the obvious criteria of a hybrid, having previously shown intermediate plumage characteristics (albeit always closer to nigricans) but having the structure and jizz more consistent with bernicla. Of course, it may not be a first-generation hybrid. The possibility of it being a second-generation (or more distant) hybrid should be considered. Especially relevant here is that broods of presumed hybrid young have been recorded in nearby Chichester Harbour, West Sussex, in the recent past. In early 1989 a mixed pair of Black Brant and Dark-bellied Brent Goose were accompanied by six hybrid young which closely resembled nigricans (Barry Collins pers. comm.). Two of these hybrids subsequently returned to the same area during the following three winters. Apart from having slightly weaker neck collars they resembled their Black Brant parent in every way. Had the identification of their parents not been known it is quite probable that they may have been recorded and accepted as pure nigricans. Although I am not suggesting that the Hayling Oysterbeds bird is one of these hybrids (especially in view of the site-faithfulness of the bird since it first appeared in 1998) it does rather highlight the potential difficulties of detecting hybrids if they are not known to be such. For the sake of argument, if the other four hybrid siblings from the Chichester Harbour brood survived and appeared at a different site, it may be quite reasonable to assume that they would have been accepted as nigricans. Hybrids between other species of wildfowl also frequently appear much closer in appearance to just one of the parent species rather than just having obvious features of both. Additionally, there are examples of hybrids which have changed their appearance as they have aged One such hybrid concerns a drake Ferruginous Duck x Pochard which has been returning each winter (from November 1999) to the Langstone Harbour area. In it�s first winter the plumage features that contributed to it being identified as a hybrid mostly became more obvious, particularly it�s dark breast. It�s reappearance in the winter of 2000/2001 as an adult (it has also returned in the present winter, 2001/2002), saw it looking different in that it had gained features (primarily a reddish-mahogany colour to the breast and a white belly) that made it look more like a pure Ferruginous Duck. Crucially, however, is that it has always shown structural features, subtle as they are, indicating it is a hybrid.[For more notes on this bird in the winter of 1999-2000, check Nigel Crook�s website: www.geocities.com/birding4ever/hybrids1.html or, for notes on it's reappearance in winter 2000-2001, see Nigel's comments on Surfbirds at: www.surfbirds.com/wwwboard/messages/13.htm] Further afield, in Berkshire, another Aythya hybrid that returned for it�s second year (but not since) to the same gravel pit in Maidenhead, changed it�s appearance between the two years. Presumed to be a Greater Scaup x Tufted Duck hybrid, the white blaze at the front of the face above the bill (the �Scaup-faced� appearance) had diminished when it returned in the second year, but, conversely, it had developed paler patches on the sides of the head. This particular individual was, however, still an obvious hybrid (Chris Heard pers. comm.). These examples show that hybrids can change their appearance with the passage of time. If their appearance moves closer to one of their parent species serious identification problems can ensue. The same situation may be the case with the Hayling Oysterbeds goose (regardless of whether Black Brant is regarded as a separate species or just a race of Brent Goose). The consequence of a Black Brant interbreeding with a Dark-bellied Brent Goose could be the same - the production of hybrid or intergrade young which not only strongly resemble just one of the parents, but young which further develop those features. This is clearly not the first Brent Goose to appear in Britain showing characteristics of nigricans but not convincingly so. Likewise, I am not the first observer to question the integrity of a bird which some observers have not. Poorly marked Black Brants (or hybrids/intergrades) have sparked controversy before and will continue to do so. However, this particular individual has an interesting history of plumage change that may add weight to my suspicions that it is not quite what it may now appear to be. |
| Reserve between 13 November 1999 and 18 February 2000 |
| HAMPSHIRE (Grid Refs. SU7103/SU7104) |
| An interesting Brent Goose in Langstone Harbour, Hampshire, England |