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ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia

Dark-bellied or pale-bellied Brent Goose (Nov 7, 2020, Netherlands, Coast) (1 Viewer)

Frank-birding

Frank van de Velde
Supporter
Dark-bellied or Pale-bellied Brent Goose (Nov 7, 2020, Netherlands, Coast)

A week and a half ago I saw this Brent Goose at the Brouwersdam (Zeeland/Zuid-Holland (Sealand, South-Holland), Dutch Coast). Is it a Dark-bellied or Pale-bellied Brent Goose? For me too hard to see from this angle unfortunately. The bird in front also has somewhat extensive white on its flanks (but dark-bellied nonetheless I’d assume), the many other Brent Geese around the Brouwersdam had less white on their sides.

Can anybody help me solve this ID?

Frank
 

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Nutcracker

Stop Brexit!
Anyone considered "Grey bellied Brent"? Recently identified in North Norfolk.
Or a hybrid/intergrade between Dark-bellied and Pale-bellied, which is much more likely in Europe than Grey-bellied (itself argued as a hybrid/intergrade between Pale-bellied and Black) :t:
 

Frank-birding

Frank van de Velde
Supporter
That could be a possibility. Both birds had lightly coloured flanks compared to surrounding birds. Although initially I didn't really take notice. Only later when I saw this bird on the same location confirmed as pale-bellied (https://waarneming.nl/observation/202973110/) I started to wonder if I hadn't overlooked something.

But I agree it's not a Pale-bellied: a distinct contrast between breast and foreflank is lacking indeed. Furthermore the colour of its back is more 'cool' than 'warm' (A pale-bellied feature I believe) and when seen 3/4th from behind (as in my images) the appearance of the flanks is lighter when compared to a more frontal view.

Frank
 
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James Lowther

Well-known member
Or a hybrid/intergrade between Dark-bellied and Pale-bellied, which is much more likely in Europe than Grey-bellied (itself argued as a hybrid/intergrade between Pale-bellied and Black) :t:

i don't think "intergrades" between dark-bellied and pale-bellied occur, as their breeding ranges are disjunct. Hybrids are a different matter though.

Grey-bellied brent should have a large neck collar however (like black brant), which the subject bird doesn't show.

cheers,
James
 

Nutcracker

Stop Brexit!
i don't think "intergrades" between dark-bellied and pale-bellied occur, as their breeding ranges are disjunct. Hybrids are a different matter though.
According to BWP juvenile geese pair up with their new lifetime mates on the wintering grounds; the female then goes off to wherever the male originated. This allows for a good level of mixing and outbreeding within populations, and also means that it is the wintering grounds, not the breeding grounds, that matter as to whether they are disjunct or not.

Lindisfarne (Northumbs) has a wintering population of around 2,000+ Pale-bellied and (in the last 20 years or so) 200+ Dark-bellied birds, which mix freely when feeding & roosting, allowing such hybridisation and intergradation to occur; I've seen presumed crosses (birds which I couldn't decide whether they were pale or dark) on a number of occasions there :t:
 

James Lowther

Well-known member
According to BWP juvenile geese pair up with their new lifetime mates on the wintering grounds; the female then goes off to wherever the male originated. This allows for a good level of mixing and outbreeding within populations, and also means that it is the wintering grounds, not the breeding grounds, that matter as to whether they are disjunct or not.

Lindisfarne (Northumbs) has a wintering population of around 2,000+ Pale-bellied and (in the last 20 years or so) 200+ Dark-bellied birds, which mix freely when feeding & roosting, allowing such hybridisation and intergradation to occur; I've seen presumed crosses (birds which I couldn't decide whether they were pale or dark) on a number of occasions there :t:

Sorry but you’re describing “hybridisation” not “intergradation”...
Intergradation posits the existence of entire areas where entire populations of intermediate animals exist.

https://en.m.wikipedia.org/wiki/Intergradation

This is not the case with pale and dark-bellied hybrids. OTOH grey-bellied are intergrades between black and pale-bellied, appearing as a distinct population breeding in an area that bridges the ranges of the two pure subspecies

Cheers
james
 

Nutcracker

Stop Brexit!
Sorry but you’re describing “hybridisation” not “intergradation”...
Intergradation posits the existence of entire areas where entire populations of intermediate animals exist.

https://en.m.wikipedia.org/wiki/Intergradation

This is not the case with pale and dark-bellied hybrids. OTOH grey-bellied are intergrades between black and pale-bellied, appearing as a distinct population breeding in an area that bridges the ranges of the two pure subspecies

Cheers
james
Semantics.

I've also (and more often) seen the definition 'If it is between two species, it is hybrids, if it is between two subspecies, it is intergrades'. Note that I put "hybrid/intergrade" in my first post though, to cover both options ;)


Oh, and let's not forget that many consider Grey to be a distinct subspecies in its own right, only minimally mixing with other subspecies :t:
 
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Deb Burhinus

Used to be well known! 😎
Europe
I think it’s a complicated question and perhaps depends on how we define ‘speciation’ (which I am not going to attempt) as well as what taxonomic thinking we apply to various species and their complexes.

However, I don’t believe it’s a case of ‘semantics’ and would answer it along similar lines to James;

Some good reading here although a bit above my pay grade :smoke:
https://academic.oup.com/jhered/article/105/S1/795/2961884

I would suggest ‘hybrids’ to mean a cross between two distinct species but not mutually exclusive so as to exclude crosses between different sub-species of the same taxa or sub-species of different taxa either. The resultant offspring in this sense then, is an individual that expresses a variant of characters of either phenotype of the parent but crucially, not such an often occurring phenomena to the extent that a distinct and fertile population is formed (being limited by back-crosses or infertility) and crucially, not geographically characterised.

‘Intergrades’ however, I would suggest, are ‘intermediates’ between different pure sub-species, that are often clinal in their phenology and form genotypically distinct and self-sustaining populations in a geographical area as a result of extensive gene flow between 2 (or more) parental taxa overlapping in the contact area at the edge of the intergrade zone. Eventually, some of these self-sustaining and distinct intergrade populations may be afforded sub-species status and even full species classification. Slightly different to an intergrade zone, would be a hybrid zone where different parental taxa in a contact area will readily hybridise but the populations of both parents are stabilised in the hybrid zone and there is no transitional phenotypes or clinal variants and the hybrid zone itself remains narrow.

The key therefore, imo, does not necessarily hinge on whether ‘hybrids’ are between different species and intergrades are between sub-species but rather what the longterm outcome is as a result of two species or sub-species cross breeding and how permeable the gene barriers are between populations of the parental taxa.

PS I agree the OP are Dark-bellied!
 
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ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia
ZEISS. Discover the fascinating world of birds, and win a birding trip to Colombia
ZEISS. Discover the fascinating world of birds, and win a birding trip to Colombia
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