Wednesday, 21 November 2012

Gull musing

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
This bird was particularly pale in flight

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

This bird has very pale pigmentation over the whole body

particularly pale underwings
Note all dark bill which is not a good indicator of Glaucous genes
 Bird 3: 1st winter Oslo 11.10.2012
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?
 Bird 4: juvenile/1st winter Glaucous Gull Oslo 02.02.2012
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.

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