Cormorants to Grebes

Great Cormorant Phalacrocorax carbo

Four subspecies of Great Cormorant are generally recognised – nominate north-west European carbo (‘Atlantic Cormorant’), south/central (and increasingly also north-west) European and Asian sinensis (‘Continental Cormorant’), north-west African maroccanus (‘Moroccan Cormorant’) and west, south and east African lucidus (‘White-breasted Cormorant’). The last-listed is afforded species status by some authorities (e.g. IOC). Marion & Le Gentil (2006) recognised a separate, largely Nordic, clade within carbo, naming it ‘norvegicus’. Both sinensis and carbo are common in Britain but neither of the African forms is on the British List though their occurrence has been claimed (Kehoe 2006).

Both African forms are rather distinctive in adult plumage showing a white face, foreneck and breast (and sometimes belly also in lucidus) but their 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. Differentiating maroccanus and lucidus may not always be straightforward so a listing as maroccanus/lucidus might be most appropriate.  

Claims of adult maroccanus/lucidus might prove acceptable based on detailed notes and good photographs but details from a ringed or marked bird would be necessary for acceptance to subspecies. (updated Sept 2015 AMS).

References

Cramp, S. et al. 1977. The Birds of the Western Palearctic. Vol. 1. Oxford University Press, Oxford.

Kehoe, C. 2006. Racial identification and assessment in Britain: a report from the RIACT subcommittee. Brit. Birds 99: 619-645.

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

 

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 in Britain. Biometrics are potentially useful, however, as desmarestii is 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 November 2014 AMS).

References

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

Cramp, S. et al. 1977. The Birds of the Western Palearctic. Vol. 1. Oxford University Press, Oxford.

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

 

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 and a claim of a possible candidate has been received.

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 Sept 2015 AMS).

References

Cramp, S. et al. 1977. The Birds of the Western Palearctic. Vol. 1. Oxford University Press, Oxford.

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

 

Great White Egret Ardea alba

There are four subspecies of Great White Egret. Nominate alba breeds across Europe and Central and North-east Asia, egretta (‘American Great Egret’) breeds in the Americas, modesta (‘Eastern Great Egret’) in South and South-east Asia and melanorhynchos in Africa south of the Sahara. Formerly a ‘BB rarity’, nominate alba is now a scarce and increasing visitor to Britain (also breeding) but no other subspecies is on the British List. The subspecies egretta is, however, a potential vagrant to Britain and its occurence has been suspected. Material has been obtained from a potential specimen from Shetland and is awaiting further research. 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, however, 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 to subspecies. There will also be issues of potential captive origin to address in assessing any claim of these subspecies. (updated November 2014 AMS).

References

Cramp, S. et al. 1977. The Birds of the Western Palearctic. Vol. 1. Oxford University Press, Oxford.

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

 

Red-necked Grebe Podiceps grisegena

There are two subspecies of Red-necked Grebe. Nominate grisegena is a regular winter visitor and rare breeder in Britain whilst the North American and North-east Asian subspecies holboellii (‘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 holboellii is problematic. It may show on average more yellow on the bill in breeding plumage but firm subspecific identification rests on biometrics, holboellii being larger than the nominate subspecies.

Claims of holboellii should include biometric evidence or details from a ringed or marked bird. (updated November 2014 AMS).

References

Cramp, S. et al. 1977. The Birds of the Western Palearctic. Vol. 1. Oxford University Press, Oxford.

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.