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Horned Lark / Shore Lark 'horns'

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Old Friday 10th February 2017, 16:33   #1
Nutcracker
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Horned Lark / Shore Lark 'horns'

According to Svensson's Identification Guide to European Passerines, moult of Eremophila alpestris is "Adult and young: summer complete". So in autumn, they should be in fresh plumage with their 'horns' at their longest.

Yet in autumn (pic below; mid October), the horns are very short, barely visible, while in spring (when they ought to be at their shortest), they are at their longest and most visible.

What gives? How do their 'horns' get longer in spring? An overlooked partial moult?
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Old Sunday 12th February 2017, 06:36   #2
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Originally Posted by Nutcracker View Post
According to Svensson's Identification Guide to European Passerines, moult of Eremophila alpestris is "Adult and young: summer complete". So in autumn, they should be in fresh plumage with their 'horns' at their longest.

Yet in autumn (pic below; mid October), the horns are very short, barely visible, while in spring (when they ought to be at their shortest), they are at their longest and most visible.

What gives? How do their 'horns' get longer in spring? An overlooked partial moult?
Maybe the horns are not counted for the purpose of determining moult types, as they are characteristic for this species only and not for other larks.
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Old Sunday 12th February 2017, 09:14   #3
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Maybe the horns are not counted for the purpose of determining moult types, as they are characteristic for this species only and not for other larks.
Thanks! Though Svensson gives the moult characteristics individually for each species, not just for each family, so that shouldn't apply.
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Old Sunday 12th February 2017, 09:56   #4
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Presumably it's a hormone related thing - they get hornier in the breeding season.
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Old Sunday 12th February 2017, 10:40   #5
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Presumably it's a hormone related thing - they get hornier in the breeding season.
< groan >
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Old Sunday 12th February 2017, 21:14   #6
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I am no expert, but I'd guess that since only the males have the horns, they get longer in the breeding season for courting.
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Old Sunday 12th February 2017, 21:42   #7
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Maybe the black feathers get abraded less quickly, thus forming horns?
(based on: https://sora.unm.edu/sites/default/f...0590-p0591.pdf)
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Old Monday 13th February 2017, 00:37   #8
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Maybe the black feathers get abraded less quickly, thus forming horns?
(based on: https://sora.unm.edu/sites/default/f...0590-p0591.pdf)
Good point (pun intended!) thanks! That could well be the answer - and adding to it, the shaft should resist wear better than the vanes, creating a slenderer sharper horn?
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Old Wednesday 1st March 2017, 18:06   #9
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More details on another thread, thanks to Peter Sunesen
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