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Old Saturday 19th March 2011, 16:52   #1
John Cantelo
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Join Date: Aug 2003
Location: Canterbury, UK
Posts: 6,117
Crested vs Thekla Lark - playing the odds

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!,
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Last edited by John Cantelo : Saturday 19th March 2011 at 17:20.
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