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 Post subject: Cape Gull vs. Kelp Gull?
Unread postPosted: Sat Jan 24, 2009 12:34 pm 
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Hi all,

Recently seen at Kleinmond was a group of ~20 Cape Gulls, which also included juveniles. They were all the EXACT same size. But then noticed one of them that was SIGNIFICANTLY smaller, and had a distinctly light eye with seemingly a pale eye-ring. Here's the pic:

Image

Have discussed this bird with some guys, and it always comes back to being a Kelp Gull / (nowadays lumped together so a Cape Gull). But wouldn't you agree that this bird differs TOO much to justify it being lumped as a Cape Gull? MUCH smaller body, much finer legs, significantly smaller feet, and those eyes...

For that matter, could it be something completely different? Even considered Lesser Black-Backed, but totally out-of-range and the legs are not bright-yellow...

Whatever the case, I thought this pic made for a good topic! Your thoughts on it please?


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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Sat Jan 24, 2009 1:15 pm 
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Good question, Moegaai! :D
The replies should be interesting.

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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 10:58 am 
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This pic is a great illustration of a classification argument.

The Sasol 3rd Edition still has the Cape (Kelp) Gull (Larus vetula) and the Kelp Gull (Larus dominicanus) as two seperate species. Though both under 312.

The Roberts has both under Kelp Gull. The decision to do this is explained on P441 of Roberts VIIth Edition. "While L. d. vetula differs markedly from other Kelp Gull subspp in terms of skeletal characters, especially skull structure and is treated by some as a distinct species, there is no molecular evidence to support this split and we follow Urban et al. in treating it as a subsp of L. dominicanus."

The pic shows both birds in one clearly. Looks markedly different but the same thing in essence.


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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 11:25 am 
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I see that the ADU (avian Demography Unit) also have not officialy split the two, but yes the distinction is quite clear


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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 11:30 am 
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Thanks Guinea Pig for your inputs - very interesting.

It is interesting how the books differ on this species. Newman's lists the Cape Gull as the common one, with the Kelp Gull as a rare vagrant (even has them as separate ticks in the back). But Roberts 7 Field Guide only mentions the Kelp Gull and doesn't even make any mention of the Cape Gull!

Based on Imax's comment on the ADU, I wonder if these "powers that be" that decides on lumping or splitting of species will make a final call on this one day? I of course wouldn't mind claiming a separate tick for this one, and strictly speaking based on the Newman's ticklist that I use, I have another tick!!!

I'm such a twitcher...


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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 11:44 am 
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I have a few of those in my book, I will write my sighting in so that the day they are split i can claim the armchair tick


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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 4:49 pm 
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Moegaai wrote:
It is interesting how the books differ on this species. Newman's lists the Cape Gull as the common one, with the Kelp Gull as a rare vagrant (even has them as separate ticks in the back). But Roberts 7 Field Guide only mentions the Kelp Gull and doesn't even make any mention of the Cape Gull!

First of all, it might help to understand the taxonomic relationship of these birds. The common bird around here certainly is the Cape Gull (Larus vetula) but it has for many years, and still is by most, considered to be a subspecies of Kelp Gull (Larus dominicanus). In other words, the true taxonomic definition of these birds can be described as follows:

There is one species, called Kelp Gull (Larus dominicanus) of which a certain subspecies, Larus dominicanus vetula, occurring around the southern African coast, is sometimes considered to be a seperate species, called Cape Gull (Larus vetula).

In other words, the question is not really whether or not Kelp Gull is a seperate species but whether or not our abundant Cape Gull is a seperate species. I know, it's all semantics, but I thought it might put things a little better in perspective and this would explain why Newmans (being an older field guide) lists Cape Gull as the common one and Kelp Gull as the rare vagrant while Roberts VII lists only Kelp Gull (implicitly including Cape Gull in that one listing as it is no more than a subspecies).

Moegaai wrote:
Based on Imax's comment on the ADU, I wonder if these "powers that be" that decides on lumping or splitting of species will make a final call on this one day?

Probably not. The study of bird taxonomy is in constant flux. The Kelp Gull complex is a good example. It used to be considered as one species. Then scientists decided that they differ markedly enough to be considered seperate species and later still scientists decided that there is not enough genetic difference for them to truly be considered seperate species. In future, who knows what might come to light, or what might be considered important by scientists? We live in a time where ornithologists set a lot of store by genetic classification while in previous years scientists, lacking genetic tools, used morphological means to classify species.

For this reason, we as birders will have to accept that our life lists will probably also continually go through shrinking and growing cycles.

Moegaai wrote:
I of course wouldn't mind claiming a separate tick for this one, and strictly speaking based on the Newman's ticklist that I use, I have another tick!!!

Of course your list is your list but I wouldn't. Scientists don't always agree on everything and some scientists might still consider these as separate species but I've decided to follow the list laid down by the Percy Fitzpatrick Institute (by the way, the ADU has nothing to do with bird taxonomy, they're concerned with bird demography), whether I agree with them or not and whether other scientists agree with them or not. It's just that, if I start using the lists of other ornithological bodies, do I use their complete list or only the few entries that differ from that of the Fitztitute and that suit me? I mean, if I choose to split Cape Gull and Kelp Gull on my list, it probably means that I should lump Grey-backed and Green-backed Camaroptera. Or I can split Yellow-billed and Black Kite, but then I have to lump Karoo and Olive Thrush. It just becomes too slippery a slope.

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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 5:07 pm 
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All making Ornithology, not only birding, a very interesting subject. Thanks for your explanation Deefstes. For a novice to this, like me, it really helps getting a guru's explanation.


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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 8:09 pm 
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Thanks Deefstes for a great explanation! :clap: :clap: :clap:

I'm glad to have seen such interesting posts on this topic. And as originally mentioned, the different appearances being classified as one. :hmz:

And no, it won't be a separate tick in my life list! :twisted: BUT this dated pic will remain in my archives until they possibly one day decide to split them again! :tongue:

Hope you all had as much appreciation for this pic as I did?


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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 8:54 pm 
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Moegaai wrote:
Hope you all had as much appreciation for this pic as I did?

Absolutely! I was actually going to comment on that but forgot. Kelp Gull is indeed a super find and getting such a dynamite picture of it is pretty awesome. Now that the birds aren't listed as separate species anymore people tend to forget what a special find the nominate Kelp Gull is.

If I where you I would send this pic to Trevor Hardaker at Zestforbirds. I think he might want to publish the pic in his rarities gallery.

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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 10:03 pm 
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Good Read Deefstes! :thumbs_up:

And great photo.......... :D

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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 10:30 pm 
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Moegaai wrote:
Hope you all had as much appreciation for this pic as I did?

I sure did! 8)
As a 'fledgling birder' (to stay in the lingo) I read this topic a few times. This is a really interesting topic!

Skull and bones are different. Appearance is rather different. Size is different. Yet they are the same birds?
I wonder if the behaviour is the same, but the size difference will influence that I think.

But Moegaai, I'm waiting for your next photo! ;)

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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Mon Jan 26, 2009 10:56 pm 
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Thanks DuQues, and I appreciated your comments. Will try and find other odd ones, okay!?!? :wink:


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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Tue Jan 27, 2009 9:43 am 
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DuQues wrote:
Skull and bones are different. Appearance is rather different. Size is different. Yet they are the same birds?


That's bird taxonomy for you. On the other hand you have Long-billed Pipit and Kimberley Pipit that are virtually indistinguishable yet they are not the same birds!

There are different criteria that taxonomists use to determine species. The most obvious and oldest criteria where of course morphology. If it looks like a duck and it quacks like a duck, it's a duck. Conversely, if it doesn't it's not. :D

As better observations where made and better tools became available, the criteria also shifted a little. Taxonomists started looking at the birds' behaviour and specifically their breeding behaviour. So at this point, two birds might look very different and would, according to the older criteria have been considered separate species (think of the different colour morphs of eagles or the two forms of Brown-throated Martin or Olive Bush-Shrike), but now it transpires that they actually interbreed, leading taxonomists to the conclusion that they are indeed different looking members of one species.

But then the tools got better still and birds where observed on molecular level. It was discovered that some birds that, according to the above criteria are seperate species (ie. they look different, they act different, they don't interbreed etc.) have near identical DNA. What now? Obviously they must be one species then :wall:

But back to the gulls, and if you want to know about a real nightmare for taxonomists, consider the Lesser Black-backed Gull complex. We are remotely affected by this as the Lesser Black-backed Gull and Heuglin's Gull do show up in SA from time to time (and the Herring Gull even less often) but DuQues, you should be more familiar with these birds as they are fairly common in your neck of the woods (at least some of them).

So, there is the Herring Gull (Larus argentatus) in Europe and the American Herring Gull (Larus smithsonianus). They look the same (but not quite), they don't occur in the same regions (but sometimes they do), they can interbreed (but they usually don't) and genetically they are very similar (but not exactly). You get the idea, for the most part they appear to be one species.

But now, let's forget the Herring Gull from Europe for the moment and consider the Vega Gull (Larus vegae), occurring just across the Bering strait from the American Herring Gull's turf. It looks almost like the American Herring Gull and they can interbreed, but it doesn't resemble the Herring Gull all that much anymore and they don't occur anywhere close to each other to even try to interbreed.

Moving further west along the arctic circle, we now encounter the Birula's Gull (Larus birulai) which again, looks a lot like the Vega Gull and they can interbreed but it is starting to look conspicuously different from American Herring Gull and even more so from Herring Gull.

But the trend continues because further along the arctic circle we get the Heuglin's Gull (Larus heuglini) and yes, you guessed it, it looks like the East Siberian Gull and they can interbreed but it doesn't quite look like the Vega Gull, less like the American Herring Gull and not anything like the Herring Gull.

In the western parts of Siberia we get the Siberian Lesser Black-backed Gull (I don't even know the scientific name) which continues the trend and finally, back in north-western Europe, we get the Lesser Black-backed Gull, similar in many respects to the Siberian Lesser Black-backed Gull but nothing remotely similar to the Herring Gull with which it co-exists as this picture taken from Wikipedia illustrates.
Image

So we have a ring of birds, circling the arctic. At any one point along the ring you can't quite tell the difference between the birds (and not even can they themselves as they do interbreed) but where the extremes meet there can be no doubt that the birds are of seperate species. So the million dollar question is, where should taxonommists draw the line? How many species are there along this circle? Looking at the extreme ends of the ring there certainly are at least two species but how many are there in between.

Speaking of taxonomic issues that will probably never be resolved, here is a prime candidate. :mrgreen:

And this is all put quite simply, the matter is much worse than just this because on some points along this ring it touches with other rings that branch off in other directions (the Vega Gull for instance doesn't only have unclear relationships to the Lesser Black-backed Gull complex but also to the Caspian Gull / Mongolian Gull complex. Many of the birds mentioned above have different subspecies (like Heuglin's Gull having at least three subspecies) and some of them are still not considered species in their own right (like Siberian Lesser Black-backed Gull or Birula's Gull). It's really one big mess.
:hmz: :huh:

And I don't think birders and taxonomists always have the same agenda :mrgreen:

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 Post subject: Re: Cape Gull vs. Kelp Gull?
Unread postPosted: Tue Jan 27, 2009 10:07 am 
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EXCELLENT read, thanks Deefstes!!! :clap:

Wasn't there a simpler hobby we could have pursued!? :doh: :lol:


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