Grebes to Cormorants

Red-necked Grebe Podiceps grisegena

Two subspecies of Red-necked Grebe are recognised. Nominate grisegena is a regular winter visitor and rare breeder in Britain whilst the North American and north-east Asian subspecies holbollii (‘Holboell’s Red-necked Grebe’) is on the British List based on a single specimen record which pre-dates BBRC. There are also at least five records for Iceland.

Identification of holbollii is problematic. It may show on average more yellow on the bill in breeding plumage but firm subspecific identification rests on biometrics, holbollii being larger than the nominate subspecies.

Claims of holbollii should include biometric evidence or details from a ringed or marked bird. (updated Dec 2017 AMS).

References

McGowan, R. Y. 2006. Comments on ‘Holboell’s Red-necked Grebe’ in wester Ross in 1925. Brit. Birds 99: 481.

Ogilvie, M. & Rose, C. 2002. Grebes of the World. Bruce Colman, Uxbridge.

 

Night-heron Nycticorax nycticorax

There are two subspecies of Night-heron in the northern hemisphere. Nominate nycticorax breeds across Europe, Asia and Africa and is a regular rarity in Britain. The North American and northern South American subspecies hoactli (‘North American Night-heron’) is not on the British List but is a potential vagrant.

At least some adult hoactli are distinguishable by face pattern and bare part colouration but biometrics are most useful.

Claims of hoactli accompanied by detailed notes and good photographs might be acceptable but biometric evidence or details from a ringed or marked bird would provide more solid evidence. There will also be issues of potential captive origin to address in assessing any claim of this subspecies. (updated Dec 2017 AMS).

References

Hancock, J. & Kushlan, J. 1984. The Herons Handbook. Croom Helm, London.

 

Great White Egret Ardea alba

Four subspecies of Great White Egret are recognised. Nominate alba breeds across Europe and Central and north-east Asia, egretta (‘American Great Egret’) in the Americas, modesta (‘Eastern Great Egret’) in South and South-east Asia and melanorhynchos in Africa south of the Sahara. The subspecies egretta has been mooted as a potential split.

Formerly a ‘BB rarity’, nominate alba is increasingly common in Britain and now breeds here. No other subspecies is on the British List. The subspecies egretta is, however, a potential vagrant to Britain and its occurrence has been suspected. The subspecies modesta is perhaps also a potential, though less likely, vagrant.

Identification to subspecies is problematic. Bare part colouration may be useful though there is significant seasonal and individual variation within each subspecies. Biometrics are potentially more useful, both egretta and modesta being smaller than nominate alba.

Claims of any extralimital subspecies accompanied by detailed notes and good photographs are welcomed but biometrics or details from a ringed or marked bird are likely to be minimum requirements for acceptance. There will also be issues of potential captive origin to address in assessing any claim of these subspecies. (updated Dec 2017 AMS).

References

Hancock, J. & Kushlan, J. 1984. The Herons Handbook. Croom Helm, London.

 

Shag Phalacrocorax aristotelis

Three subspecies of Shag are recognised. Nominate aristotelis is a common breeding bird in Britain but there are also two southern subspecies – desmarestii (‘Mediterranean Shag’) from the Mediterranean and Black Sea and riggenbachi (‘Moroccan Shag’) from coastal Morocco (though the latter is now rare). Neither of these two latter subspecies is on the British List though the occasional occurrence of desmarestii has been suspected and it is presumably a potential vagrant.

The identification of desmarestii is problematic, however. Adults closely resemble nominate aristotelis, differing only in bare part colouration, but immatures show marked differences in the colour of the underparts. However, a small proportion of birds fledged in Britain appear similar and such birds may account for the few suspected occurrences of desmarestii here. Biometrics are potentially useful, however, desmarestii being smaller than nominate aristotelis.

Claims of desmarestii accompanied by detailed notes and good photographs are welcomed but biometric evidence or details from a ringed or marked bird are likely to be minimum requirements for acceptance. (updated Dec 2017 AMS).

References

Brown, J .G. 2004. Juvenile Shag on Skomer showing characteristics of Mediterranean race. Brit. Birds 97: 96-97.

Flumm, D. S. 1993. Do Mediterranean Shags occur in southwest England? Brit. Birds 86: 166-173.

 

Cormorant Phalacrocorax carbo

Three Western Palearctic subspecies of Great Cormorant are recognised – nominate north-west European carbo (‘Atlantic Cormorant’), south/central (and increasingly also north-west) European and Asian sinensis (‘Continental Cormorant’) and north-west African maroccanus (‘Moroccan Cormorant’). Marion & Le Gentil (2006) recognise a separate, largely Nordic, clade within carbo, naming it ‘norvegicus’.

Both sinensis and carbo are common in Britain but maroccanus is not on the British List.

The subspecies maroccanus is rather distinctive in adult plumage, showing a white face, foreneck and breast, but its appearance may be approached by occasional (aberrant?) individuals of the two European subspecies. Separation in immature plumages seems to be poorly understood and there appear to be few useful biometric differences. The subspecies maroccanus would also need to be distinguished from the similar (and now split) African Cormorant P. lucidus which occurs south of the Sahara.

Claims of adult maroccanus might prove acceptable based on detailed notes and good photographs but details from a ringed or marked bird would be preferable (and required for other plumages). (updated Dec 2017 AMS).

References

Marion, L. & Le Gentil, J. 2006. Ecological Segregation and Population Structuring of the Cormorant Phalacrocorax carbo in Europe, in Relation to the Recent Introgression of Continental and Marine Subspecies. Evolutionary Ecology 20: 193-216