Wayne Richardson
10-23-2008, 05:51 PM
While researching gull literature to answer William’s ID query, I came across significant developments in gull taxonomy.
At one time it was thought that the Herring/Lesser Black-backed gull complex was a classic example of a ring species. From the very dark nominate race of Lesser Black-backed in the Baltic, birds gradually got paler as you travelled eastwards across northern Siberia, America & the Atlantic to the Herring of UK/Scandinavia. Individuals then quickly darkened through the 2 other races of Lesser Black-backed (graellsii & intermedius) across UK/Scandinavia & then back to fucus
Although some races appear to inter-breed quite freely, Herring & Lesser Black-backed have nested in mixed colonies with very little inter-breeding. There was also the very pertinent question of how did the southern ring of pale mantled & mainly yellow-legged gulls across the Mediterranean, Black/Caspian Seas & central Siberia fit into the equation.
With the advent of mtDNA & much improved birding techniques, it became clear that some races were species in their own right. Genetic studies threw up some real surprises, i.e. Herring Gulls in NW Europe are more closely related to both Glaucous & Greater Black-backed than their American cousins. In fact, Herring Gulls in the American were actually much closer to Lesser Black-backed. The family similarity is most obvious in the dark juveniles.
The consensus is that gull diversity has been most affected by the Ice Ages. With each advance & retreat (reckoned to about 20 in total) they eventually developed into the bewildering mix of gulls we see today. At the height of each cold spell, the ancestors of our modern gulls existed in 2 refuges (clades) situated ed in the North Atlantic & the Aral/Caspian Seas. With each thaw, the gulls initially spread northwards, then either east or west & even in both directions. There is evidence of some species now spreading southwards & overlapping with other species/races going in the opposte direction. It is interesting that a colony of yellow-legged Herring Gulls in Finland in the 1950's was completely swamped range expansion by pink-legged birds in only a few decades & is now extinct.
The BOURC have, in line with with other European bird committees, decided to recognised the species listed below:
Caspian Gull Larus cachinnans
Lesser Black-backed Gull Larus fucus with 6 SSP comprising of nominate Baltic Gull, graellsii, intermedius, heuglini Heuglin’s Gull, taimyrensis & barabensis.
American Herring Gull Larus smithsonianus with 3 SSP comprising of nominate, vegae Vega Gull & mongolicus Mongolian Gull.
European Herring Larus argentatus with 2 SSP comprising of nominate & argenteus
Yellow-legged Gull Larus michahellis with 2 SSP comprising of nominate & atlantis, but some other populations may deserve SSP status.
Armenian Gull Larus armenicus
These decisions endorse several recommendations put forward in ‘Gulls of Europe, Asia & North America – Olsen & Larsson’. The AOU have not (yet?) adopted these changes.
There is acknowledgement that as research continues, so some SSP named above may also prove to be credible species, while others perhaps belong with another group. An interesting case in point relates to the taimyrensis Lesser Black-backed. It is considered by some authorities to be a hybrid between Heuglin’s & Vegae Gulls in much the same way that Kumlien's Gull exists between Iceland & Thayer's.
An example of the complexity of gull taxonomy is borne out by that fact that all the listed gulls shared a common ancestor as recently has 300,000 years ago. Some of the newly designated species do not interbreed, even when in a mixed colony. On the other hand, Glaucous-winged & Western last shared an ancestor over a million years ago, but are freely interbreeding in a wide contact zone.
It is also worth noting that the group comprising Glaucous-winged, Western & Yellow-footed Gulls is actually a very good example of a ‘light to dark’ cline, but these are all seen as good species. From north to south they show the full range from pale mantle & primaries to dark mantle & primaries. All these gulls are big & bulky with distinctive short broad wings. Slaty-backed Gull is a western off-shoot of this particular group & shares the same basic jizz with the others.
Given recent discussions regarding the Louisiana hybrid gull colony on William’s ID thread, it is interesting that Kelp & American Herring Gulls both originated in the same Aralo-Caspian clade. Kelp has proved to be an early southern off-shoot from a Lesser Black-backed predecessor.
I’ve tried to keep this simple & straightforward.
Cheers: Wayne.
At one time it was thought that the Herring/Lesser Black-backed gull complex was a classic example of a ring species. From the very dark nominate race of Lesser Black-backed in the Baltic, birds gradually got paler as you travelled eastwards across northern Siberia, America & the Atlantic to the Herring of UK/Scandinavia. Individuals then quickly darkened through the 2 other races of Lesser Black-backed (graellsii & intermedius) across UK/Scandinavia & then back to fucus
Although some races appear to inter-breed quite freely, Herring & Lesser Black-backed have nested in mixed colonies with very little inter-breeding. There was also the very pertinent question of how did the southern ring of pale mantled & mainly yellow-legged gulls across the Mediterranean, Black/Caspian Seas & central Siberia fit into the equation.
With the advent of mtDNA & much improved birding techniques, it became clear that some races were species in their own right. Genetic studies threw up some real surprises, i.e. Herring Gulls in NW Europe are more closely related to both Glaucous & Greater Black-backed than their American cousins. In fact, Herring Gulls in the American were actually much closer to Lesser Black-backed. The family similarity is most obvious in the dark juveniles.
The consensus is that gull diversity has been most affected by the Ice Ages. With each advance & retreat (reckoned to about 20 in total) they eventually developed into the bewildering mix of gulls we see today. At the height of each cold spell, the ancestors of our modern gulls existed in 2 refuges (clades) situated ed in the North Atlantic & the Aral/Caspian Seas. With each thaw, the gulls initially spread northwards, then either east or west & even in both directions. There is evidence of some species now spreading southwards & overlapping with other species/races going in the opposte direction. It is interesting that a colony of yellow-legged Herring Gulls in Finland in the 1950's was completely swamped range expansion by pink-legged birds in only a few decades & is now extinct.
The BOURC have, in line with with other European bird committees, decided to recognised the species listed below:
Caspian Gull Larus cachinnans
Lesser Black-backed Gull Larus fucus with 6 SSP comprising of nominate Baltic Gull, graellsii, intermedius, heuglini Heuglin’s Gull, taimyrensis & barabensis.
American Herring Gull Larus smithsonianus with 3 SSP comprising of nominate, vegae Vega Gull & mongolicus Mongolian Gull.
European Herring Larus argentatus with 2 SSP comprising of nominate & argenteus
Yellow-legged Gull Larus michahellis with 2 SSP comprising of nominate & atlantis, but some other populations may deserve SSP status.
Armenian Gull Larus armenicus
These decisions endorse several recommendations put forward in ‘Gulls of Europe, Asia & North America – Olsen & Larsson’. The AOU have not (yet?) adopted these changes.
There is acknowledgement that as research continues, so some SSP named above may also prove to be credible species, while others perhaps belong with another group. An interesting case in point relates to the taimyrensis Lesser Black-backed. It is considered by some authorities to be a hybrid between Heuglin’s & Vegae Gulls in much the same way that Kumlien's Gull exists between Iceland & Thayer's.
An example of the complexity of gull taxonomy is borne out by that fact that all the listed gulls shared a common ancestor as recently has 300,000 years ago. Some of the newly designated species do not interbreed, even when in a mixed colony. On the other hand, Glaucous-winged & Western last shared an ancestor over a million years ago, but are freely interbreeding in a wide contact zone.
It is also worth noting that the group comprising Glaucous-winged, Western & Yellow-footed Gulls is actually a very good example of a ‘light to dark’ cline, but these are all seen as good species. From north to south they show the full range from pale mantle & primaries to dark mantle & primaries. All these gulls are big & bulky with distinctive short broad wings. Slaty-backed Gull is a western off-shoot of this particular group & shares the same basic jizz with the others.
Given recent discussions regarding the Louisiana hybrid gull colony on William’s ID thread, it is interesting that Kelp & American Herring Gulls both originated in the same Aralo-Caspian clade. Kelp has proved to be an early southern off-shoot from a Lesser Black-backed predecessor.
I’ve tried to keep this simple & straightforward.
Cheers: Wayne.