Tuesday, November 25, 2008

Herring Gull vs Iceland Gull vs Thayer's Gull.

Adult breeding plumage Herring Gull

3rd cycle Herring Gull

3rd cycle Ring-billed Gull

Adult breeding plumage Ring-billed Gull

Herring or Thayer's? 

Gulls. Herring and Ring-billed are pretty simple.  They're your everyday "seagull". 
But what about the other gulls? Well, Great Black-backed is fairly easy. It's much bigger than anything else.  Adult Lesser Black-backed is also fairly simple. It's darker backed than the surrounding Herring Gulls and is bigger than the Ring-bills.  What if you added Slaty-backed or Kelp Gull? again, they are much much darker mantled than most of the other gulls you'll see around here. Slaty-backed is dark dark black and Kelp is even darker. 
Then what happens if you added Glaucous, Glaucous-winged and Iceland you say. Same thing except backwards.  GLGU, GWGU and ICGU are all much lighter in color than Ring-billed or Herring. Neither do they have black primaries which makes ID all the easier. 

But what about the tricky ones.  Let's try Thayer's Gull.  Thayer's Gulls are identical to Herring Gulls in every way, except for three small differences.  Adult Thayer's Gulls have dark eyes, no black on the underside of the primaries, and brighter, richer pink legs. 

How many times have you picked through a huge flock of gulls at a dump while looking for a Thayer's Gull?  Has someone reported a Thayer's minutes ago only for you to miss it?  Why is this? Imagine that the other birder has exactly the same skill level you do. He picks out the Thayer's. You can't. Why? 

Because if you take into account the variations in plumage and regional plumage variation in both species, you will find that the two species are impossible to tell apart with any certainty. 

Now, add a dark Iceland Gull and a light Thayer's Gull. Once again, they are practically impossible to tell apart.  
Now think of all the things that to you, constitute a Thayer's Gull. 
Bright pink legs? Dark eye? Lack of black on the underside of the primaries? Amount of white on the "windows"? 
Then think of all the variations in gull plumage that you've ever seen. Think of all the reports of aberrant gulls and weird looking gulls and darker-backed Herring Gulls, Herring Gulls with a minimal amount of black on the underwing tips......  
Taking all that into account, are the field marks that you use to ID a Thayer's Gull really sufficient to actually confidently ID a Thayer's Gull?  

I didn't think so.  

Ask yourself, do we even know much about Thayer's Gulls?  Look at all the other Gulls in North America and then compare to Thayer's.  Compared to other gulls, we have very little idea about where Thayer's nest, how they nest, what the incubation period is, what the fledging period is, or even the exact time of year they start nesting.  Why is this? Surely not because they nest in remote areas.   
Here and here you can read what little we know about these birds. 

You can probably see where this is heading.  Ok, I'll get to the point. 


Should it?  But even if we lump it, it doesn't completely solve the ID problem.  
If it should be lumped, it would be lumped with ICELAND GULL.  This doesn't help us at all. 
Now, instead of trying to ID Thayer's vs Iceland, we'll be trying to ID the Thayer's subspecies of Iceland Gull from Herring (which by the way, is considerably harder). 
That leaves us back at square one.  

So then what about Iceland?  Should Iceland be considered a full species?  Most people would reply yes.  Iceland Gull is considerably easier to ID. Most Icelands are missing the black primaries of Ring-billed and Herring. 
So leave Iceland alone. 

Let's try lumping another two species. THAYER'S AND HERRING. That would solve all our ID problems.  Larus argentatus thayerii would be much easier on us birders than Larus glaucoides thayerii. 

Why not? it's easy, it's simple.  The two species are identical anyway so why try to ID a bird that you can't ID with any certainty? 

Let's hear your thoughts on the subject.  Anyone?  Post your thoughts in the comments section.

You can vote your answer in the polls just to the right of this post. 


Tim H said...

I don't think visual differences/similarities in the field should play a big part in taxonomy. It's about how species are relative to one another, not whether birders can positively tell them apart in the field (though us birders would like it be).

But I'm not a taxonomist, or a gull expert, so I'll leave it to them to decide. I guess you can consider THGU and HERG conspecific, nobody is forcing you to follow what the AOU/ABA says.

Squid said...

Your pic is two herg's...

Thayer's and Iceland would be the logical lump, as there are numerous occasions where a gull could be either (ie a hybrid). Kumlien's Gulls are what some people think of as this hybrid. Others think it's a subsp. of Iceland. To lump HERG and THGU wouldn't work - they can quite easily be told apart in the field (at all ages) by using all the field marks (not one specific one) - some thayer's can have light eyes, but they also fit the white underwings, bright pink legs, rounder head, and generally smaller size.

TimH - people and gorillas are only 2% different DNA - should we be the same species? (although sometimes I think we are...) DNA should definitely play a part in taxonomy - but is it everything?

Parus said...

I don't think Thayer's can be told quite as easily as you think. Anyone who thinks they can ID Thayer's vs Herring easily, needs to rethink what they're using to ID Thayer's Gull. There's just too much variation in Herring Gull to make any ID a certain one.
I have personally seen gulls that people have called Thayer's that just turned out to be a Herring with a little brighter legs, or a darker eye and vice versa.
Personally, taking into account the variation in plumage, I don't think it's possible to ID a Thayer's with any accuracy. I'll take "potential" Thayer's but not "certain" Thayer's.
Visually, Thayer's and Iceland are two completely different birds. Kumlien's has to be one of the most difficult to ID because of the Hybrid possibilities.

BTW, yes the photo is of two Herring Gulls. But mostly because Thayer's doesn't occur this far south in early summer.

JoshC said...

Yes, there is some complication to the Thayer's/Kumlien's/Iceland gull complex, but there is almost no confusion with Thayer's and Herring.

I am just guessing that the Midwestern states don't get as many THGU, and meaning you don't seem many, but you do have the great lakes, so never mind that.

You are a great friend to me, and don't take this personally, but you are quite wrong with the "only 3 marks" to distinguish THGU and HERG. Winter adults are easy to tell, and so is all the ages. You need to focus on the jizz of the bird too. Thayer's have a lighter build and smaller bill. In juvie/first/second year birds, Thayer's has more creamy dark brown primaries, as HERG has jet black (can bleach to really dark brown) In the flight the two-toned paneling on the primaries in quite visible.

Maybe you need to visit my dump, up here next November. Dan Casey and I will tutor you in Gulling. hehe

Check out my "Gulls 101" blog post.

Squid said...

We get quite a few THGU's up here in the Sault too. No offense meant in my post, I was just stating the truth that if you take the whole gull into account, they can be fairly easy to ID (provided there is a decent look involved).