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-   -   Crested vs Thekla Lark - playing the odds (https://www.birdforum.net/showthread.php?t=195118)

John Cantelo Saturday 19th March 2011 16:52

Crested vs Thekla Lark - playing the odds
 
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There's been a lot of discussion recently about the identification of Thekla & Crested Lark. This has encouraged me to muse about the mechanics of bird ID. To a large degree, I concluded, birding is all about 'playing the odds'. Given a good, extended, close views there's usually little room to doubt about a birds identity. Even a distant group of 'marsh terns' in the UK can almost certainly be ID's as Black Tern; not 100%, but pretty darn close. The same birds observed in southern Spain could also be Black Tern, but are just (more?) as likely to be Whiskered Tern. It's all about playing the odds and thinking about probabilities.

Then again there are those species that almost always need a decent view to allow any degree of certainty. Telling Thekla Lark from Crested is one such example of this. However, even here it might be useful to 'play the odds' to make your ID more certain.

So with some trepidation I'm going to attempt to have a systematic look at the Thekla/Crested problem. I've tried to put the criteria in a heirarchy and weighted points according to my own experience. To this end I have attached a 'crib sheet' which may prove useful in provoking debate/clarifying ideas. Naturally, others will give a different weight to some features, but I hope this makes a good starting point. (Note that my comments refer to the situation in Iberia).

I've put a slightly fuller version of this on my web/blog (see below), but my photos are so poor that I hesitate to post them here. So I'm hoping that this post will encourage better photographers to post images here to highlight/clarify the points on my sheet. Please comment/refine my ideas - I don't claim omniscience and still find the odd bird I decide to 'walk away' from!,

John Cantelo Monday 21st March 2011 08:54

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What? No responses?

I was rather hoping for some debate/argument on my take on this ID matter! Better still I had hoped that it might elicit some comparative photos showing these points.

In the absence of anything else I've posted two rather indifferent photos to illustrate just how distinct the bill shape can be. Incidentally, the Thekla in the photo had a rather poorly marked chest - similar to many Crested - so the bill shape (plus the location) was particularly useful,

Trystan Monday 21st March 2011 09:26

I have a few birds on my list which are there based on likelihood rather than solid identification.

I visit Spain regularly and still don't have much confidence seperating these two species but on balance, I'm confident that at least some have been Thekla.

In your opinion, as Thekla are more prone to perching up but less prone to being around built up areas, would a bird perched on a house roof in hilly country where the houses are new (i.e. formerly good thekla habitat) be more likely a Thekla or a crested lark?

Brian J Small Monday 21st March 2011 09:37

Comparative image posted on Surfbirds by Stephen Daly in Spain - http://www.surfbirds.com/media/galle...0312055228.jpg

Brian S

John Cantelo Monday 21st March 2011 16:04

Quote:

Originally Posted by Brian J Small (Post 2093555)
Comparative image posted on Surfbirds by Stephen Daly in Spain - http://www.surfbirds.com/media/galle...0312055228.jpg

Brian S

An excellent comparison - well worth a look.

Everyone 'sees' birds in a subtly different way, but for me judging bill shape is the single most important feature and, arguably, the most reliable one. Presumably, bill shape reflects feeding strategies. Feeding in 'softer' ground the Crested's longer curved bill might aid probing. Thekla, being habituated to 'harder' ground may have less use for probing but more for picking prey off hard surfaces.

It would be intesting to see photos of the degree of variation in the boldness of the chest streaking too.

Motmot Monday 21st March 2011 16:18

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A typical crested from my home patch (end of September):

John Cantelo Monday 21st March 2011 17:15

Quote:

Originally Posted by Motmot (Post 2093868)
A typical crested from my home patch (end of September):

Thanks for posting your photos - as a matter of interest, what time of the year were they taken?

davercox Tuesday 22nd March 2011 06:04

Re song: I agree re usual length of song, but your point about 'distinct notes' doesn't chime with my memories. Maybe I've been lucky, but so far I've always found Crested song very distinctive (short but definite phrase): and Thekla usually so (longer with less structure). I expect there are Theklas that sing Crested, though ...

Jane Turner Tuesday 22nd March 2011 06:14

Nice one John. With less experience of them, in a Spanish context I think I elevate bill shape to a 4 on your scale and downgrade crest to a 2.

John Cantelo Tuesday 22nd March 2011 06:27

Quote:

Originally Posted by davercox (Post 2094335)
Re song: I agree re usual length of song, but your point about 'distinct notes' doesn't chime with my memories. Maybe I've been lucky, but so far I've always found Crested song very distinctive (short but definite phrase): and Thekla usually so (longer with less structure). I expect there are Theklas that sing Crested, though ...

I put that 'more distinct notes' in inverted comas because I was struggling towards articulating what I felt -the phrase isn't quite right, but I can't think of a better way to say it. But then I admit that I find song, and even more so describing it accurately, very elusive. I'll have to listen to them again to be sure, but perhaps I mean that Thekla's is a bit more flowing and fewer sharp notes (whch tend to sound more distinct to me). Having said that I still often find them so similar that I'd hesitate to say which was which - for me it's often little more than a 'feeling' than a 'certainty', but, to repeat myself, my aural recall is poor so I'm pretty sure your sensitivity & descriptive powers trump mine,

John Cantelo Tuesday 22nd March 2011 06:36

Quote:

Originally Posted by Jane Turner (Post 2094340)
Nice one John. With less experience of them, in a Spanish context I think I elevate bill shape to a 4 on your scale and downgrade crest to a 2.

Thank you Jane - coming from yourself, that's a compliment indeed!

In my origina draft I rated the bill higher than the chest streaks and crest as an ID feature. The later can be altered by wear or appear different due to angle/light and even the strength/direction of wind, but, given a good view, the bill's distinction is constant. I chickened out as I know friends of mine argue that other features are equally important/obvious/distinctive. As I said we all see birds differently and my starting point with Thekla is, when possible, always the bill. Having looked at a few more photos, I think you're right about the crest too - again I was possibly swayed b a friend who rates this feature highly!

Mark Etheridge Tuesday 22nd March 2011 07:07

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This is a Crested, although the angle of the head makes the bill look more like a Thekla due to foreshortening... my other shots of this bird (not so good) with the bill sideways on shows the curvature better. I hope this is a useful view of the chest markings on this specimen.;)

Taken 23 June 2010, La Mata reserve near Torrevieja, Alicante - typical Crested territory.:t:

Stephen Fletcher Tuesday 22nd March 2011 09:38

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I would agree with all your points, bill for me is the most deciding clincher, as colour, streaking, and crest size can be extremely variable in both, and habitat can also have a large crossover. For me, jizz is the most important factor, something extremely difficult to pick up on in a still image. Calls are very similar and close birds tend not to call much so picking out which one is calling/singing can be very difficult too. I have attached a few images, a couple of which are a bit contentious as to the actual specie.

Stephen Fletcher Tuesday 22nd March 2011 09:39

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Another 2 as it would only let me upload 5.

John Cantelo Tuesday 22nd March 2011 10:08

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Quote:

Originally Posted by Mark Etheridge (Post 2094367)
This is a Crested, although the angle of the head makes the bill look more like a Thekla due to foreshortening... my other shots of this bird (not so good) with the bill sideways on shows the curvature better. I hope this is a useful view of the chest markings on this specimen.;)

Taken 23 June 2010, La Mata reserve near Torrevieja, Alicante - typical Crested territory.:t:

Thanks Mark. Good photo of the chest and a timely warning not make a snap judgement on bill shape at such a dodgy angle.

Attached is my redraft of my original table - still imperfect, but going in the right direction I hope!

Motmot Tuesday 22nd March 2011 11:09

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Three bad images of a local Thekla from this morning

John Cantelo Tuesday 22nd March 2011 13:07

Hmmm! Some interesting images there Stephen. Several look to me to be clear cut Theklas and one at least looks more like a Crested, but others look very tricky indeed! Any info on time of year? And, yes, I hesitate to be the first one to 'jump into the water' and say which one is which. I'll ponder a little longer on this!

John Cantelo Tuesday 22nd March 2011 13:10

Quote:

Originally Posted by Trystan (Post 2093547)
I have a few birds on my list which are there based on likelihood rather than solid identification.

I visit Spain regularly and still don't have much confidence seperating these two species but on balance, I'm confident that at least some have been Thekla.

In your opinion, as Thekla are more prone to perching up but less prone to being around built up areas, would a bird perched on a house roof in hilly country where the houses are new (i.e. formerly good thekla habitat) be more likely a Thekla or a crested lark?

Sorry for being so slow to come ba to you on this. I think in a sense the issue is that built up areas are less prone to appear in Thekla habitat! However, I do tend to assciate Cresteds with railway sidings and semi-derelict urban land. I've seen Crested perch on buildings but not Thekla. Howeve, I'm sure this reflects the want of houses in Thekla habitat; I'm sure they'd treat buildings pretty much as they treat large boulders on which they may often perch!

Motmot Tuesday 22nd March 2011 13:52

Quote:

Originally Posted by Mark Etheridge (Post 2094367)
This is a Crested, although the angle of the head makes the bill look more like a Thekla due to foreshortening... my other shots of this bird (not so good) with the bill sideways on shows the curvature better. I hope this is a useful view of the chest markings on this specimen.;)

Taken 23 June 2010, La Mata reserve near Torrevieja, Alicante - typical Crested territory.:t:

Could we see the other shots of this bird? Theklas can also be found at La Mata afaik ;)

Stephen Fletcher Tuesday 22nd March 2011 13:55

Quote:

Originally Posted by John Cantelo (Post 2094612)
Any info on time of year?

1: 10 Feb
2: 29 May
3: 21 Jan
4: 23 May
5: 25 April
6: 5 May
7: 28 Aug

John Cantelo Tuesday 22nd March 2011 14:05

It's moments like this when I question the wisdom of starting a thread like this since I now risk a unique double by revealing my feet are of clay whilst also managing to get a load of egg on my face! Then again I did start the thread with a view to clarify my own 'take' on this notorious pair!
Re Stephen's photos - Here goes:-
Image 1– umm …bill seems short, but shape a bit more Crested like. Very bland looking face/super. But looks whitish below with distinct streaks .. one of those birds where signals seem mixed so a reluctant CRESTED
Image 2 – due to the angle, not an awful lot to see here, but super looks a bit bland and that bill looks, as far as I can judge, more like Crested’s. A slightly ‘wobbly’ CRESTED
Image 3 - Thekla bill, smooth line to crest from lores, blotchy chest slightly ‘dumpier’ & greyish looking, bolder cheeks; nice lichen-y rock! THEKLA
Image 4– the bill look short for Crested; gut reaction says THEKLA
Image 5 – the bill says Crested, crest seems to rise above the eye, sandyish, longer more diffuse super, looks lightly marked below, bland cheeks perhaps longer primary tip - CRESTED
Image 6 - looks a bit worse for wear; blotchy chest, whiter bolder super both say Thekla. Crest looks superficially like Crested but I suspect it’s been whipped up by a breeze. Bill shape a bit “twixt & tween” but more akin our mountain friend so a THEKLA
Image 7
-another looking a bit worse for wear; not a very blotchy chest, bolder super, crest raising from behind eye. Bill looks shortish,but very evenly curved above. Ploughed field. This is one of those birds where signals seem mixed. I’d err on the side of CRESTED

Jane Turner Tuesday 22nd March 2011 14:10

Funny John, I bottled it too. I had 3,4 and 6 as Thekla, 3 being the one I was actually almost confident of!

Mark Etheridge Tuesday 22nd March 2011 16:48

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Quote:

Originally Posted by Motmot (Post 2094652)
Could we see the other shots of this bird? Theklas can also be found at La Mata afaik ;)

Here 'tiz - not the best shot but clear enough for an ID I suppose - now on tenterhooks in case it just MIGHT be a Thekla.....:eek!:

Stephen Fletcher Tuesday 22nd March 2011 17:02

3, 4 and 6 are Theklas, so your theory and logic prove correct. 3 is the "classic thekla" and so easier to identify, and although sat on a rock, it was actually in the middle of the steppe, and nowhere near high stony ground. You can see from just these few images how difficult they are to identify, made much worse when the bird refuses to sit still, or side on when in the field to enable the features to be seen clearly. I would love to see some work done on the DNA of both to see how much interbreeding actually occurs, i am sure there must be more than people would imagine. This appears to be one of the occasions when sceptics of bird identification via photos are proven wrong.

John Cantelo Tuesday 22nd March 2011 18:27

Quote:

Originally Posted by Stephen Fletcher (Post 2094808)
3, 4 and 6 are Theklas, so your theory and logic prove correct. 3 is the "classic thekla" and so easier to identify, and although sat on a rock, it was actually in the middle of the steppe, and nowhere near high stony ground. You can see from just these few images how difficult they are to identify, made much worse when the bird refuses to sit still, or side on when in the field to enable the features to be seen clearly. I would love to see some work done on the DNA of both to see how much interbreeding actually occurs, i am sure there must be more than people would imagine. This appears to be one of the occasions when sceptics of bird identification via photos are proven wrong.

Phew, Stephen, do I get a certificate? Like Jane, and as you suggest, I too thought No3 was the 'easy' Thekla out of the bunch. No5 was, I thought, the easier of the Cresteds. Mustn't get too big 'eaded as I think I might have to revisit Mark's lark now that he's posted another photo! To be honest this thread has reminded me that I must spend more time looking at larks when I'm next in Spain.

I absolutely agree that it'd be interesting to see some DNA work on Thekla/Cresteds in Spain. I too incline towards the idea that they may interbreed more often than is curently accepted. I wonder whether it's a situation like that found with Darwin's finches where species boundaries are fairly 'plastic' according to varying environmental conditions,


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