There isn’t often too much public debate about bird ID in
Norway. As is the case in other countries and other settings, there is too
much worry regarding the risk of making a mistake such that many people do not
join in debates or are very cautious. Or maybe they just don’t care! Or maybe
they are worried that the debate will become personal.......
I think though that these ID debates help improve the
collective knowledge and that far more people should be prepared to put
themselves out there.
One debate that is raging at the moment though concerns the
ID of supposed hybrid Herring x Glaucous Gulls (gråmåke x polarmåke), see here
and here (all in Norwegian). Birds, and especially juveniles/1st winters, showing
what could be described as hybrid characters are regularly seen around the
coast of Norway including Oslo. One camp centred around larophiles in Bergen
treats these birds as being hybrids whereas the majority of other Norwegian
larophiles (which isn’t a particularly large group of people) treat these as
extremely pale Herring Gulls ssp argentatus. The public debate has unfortunately
reached a stale mate position with protagonists not looking like they will
budge an inch which is unfortunate......
The pro hybrid camp claims to follow the same line as gull
experts in Ireland and Canada who also call these birds hybrids, whilst the pale
Herring Gull camp jokingly have suggested we need a new taxon “Bergenshybrid”
but also claim to follow the same line as the Finns!
When I first encountered one of these birds I believed it
must be a hybrid but once I realised how frequent they were and how infrequent
Glaucous Gulls were in the Oslo areae then the possibility of them being hybrids just didn’t seem
realistic so I drifted to the pale Herring Gull line of thought. They also turn
up early and ringing recoveries show some at least to have hatched in southern
Norway to “normal” looking Herring Gulls. Also, other than a single occurrence there
are no suggestions of hybrid pairs of Glaucous and Herring Gulls in middle or
southern Norway.
It should also be noted that these birds do not resemble the
classic hybrid which is also known as Nelsons Gull. Instead, if I understand
the arguments of the Bergen camp correctly these are not necessarily first
generation hybrids, or even second generation come to that, but they possess
some Glaucous Gull genes.
Here by the way are some of these birds I have photographed close
to Oslo so that we have something to refer to.
Bird 1: juvenile/1st winter Drøbak, near Oslo 06.02.2012
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| This bird was particularly pale in flight |
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| The closer bird is the possible hybrid with a similarly aged Herring Gull behind. Note the bill on this individual is 2-toned |
Bird 2: juvenile/1st winter Oslo 11.10.2012
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| This bird has very pale pigmentation over the whole body |
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| particularly pale underwings |
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| Note all dark bill which is not a good indicator of Glaucous genes |
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| This bird is a Herring Gull but I include it to show how similar it is to Bird 2 except for the darker centred tertials and primaries (which are pale edged). The similarity of this bird to the one above makes me ask the question where to draw the line? |
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| just to give a reminder of some of the features a hybrid should be showing |
Now I am no gull expert and doubt I have it in me to become
a larophile but I feel qualified to have some opinions on this subject.
Large White Headed Gulls (LWHG) are seen as being little
developed in evolutionary terms such that hybridisation occurs frequently
between the many species. One could raise the question as to whether they are
true species, and indeed it is only in recent years that many have been split,
but I will leave the “what is a species” discussion to another time.
If there are such small genetic differences between them and
hybridisation is so common (in certain overlap zones) and has occurred for so
long (as the argument goes) then I would imagine that the majority of Herring
Gulls contain some alien genes which may explain the HUGE variation one sees in
the appearance of young Herring Gulls. Why do we pick on the ones at the palest
end of the spectrum and try to label them as hybrids with Glaucous Gull? Where
do we draw the line? As you saw in the
pictures above the third bird is very similar to the second except for darker
tertials and primaries (still pale fringed). What is the clincher to say a bird
has Glaucous genes?
It looks to me that there is a PhD study waiting here for
somebody to determine the DNA of all these LWHGs and see if there are real
differences between the so called species and then try to determine what these
hybrid intermediates are. For me though to call these birds hybrids just
because they possess some characters of Glaucous and then point to the fact
that hybridisation is so widespread as the proof is wrong. If these birds (or
their parents, or grandparents....) stem from the hybrid zone then why is it
only the hybrids that turn up in southern Norway in any numbers and with such
regularity? Why do they outnumber pure Glaucous Gulls so much and why do we not
see any Nelsons Gull type hybrids?
I prefer to think of them as pale Herring Gulls - without any proof. Where the
paleness comes from I am not qualified to say but it is clearly a lack of
pigmentation. As to what causes this pigmentation loss then it could be due to
some genetic Glaucous Gull influence but where did that influence come from? As
Glaucous and Herring Gulls are so recently evolved and share the same ancestral
mother LWHG then surely this genetic mother had both Herring and Glaucous Gull
genes and maybe she left some of the Glaucous Gull genes in Herring Gulls which
express themselves every now and then in pale juveniles/1st winters?
Another option is that maybe there IS a new species waiting
to be described.
We have the whole Thayer’s, Kumleins, Iceland Gull melting pot. Maybe on our
side of the Atlantic there is actually a stable hybrid population generated
from Glaucous and Herring Gulls (with variable appearance) just waiting to have
a name put on it! :-)
Whatever the answer I must admit to enjoying finding one of
these birds because for a minute or two you think you have found something
rarer.
Nice looking gulls ...
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