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Thursday, August 07, 2008

Moult in birds

The woods which were so alive with bird song and nesting activity only a few weeks ago now seem quiet and deserted. Only occasionally is a bird to be seen flitting through the forest canopy, or heard chirping from some scrub. Where have they gone?

The answer is that they are still mostly there, but undergoing their moult. Without this annual replacement, feathers will wear out by abrasion, deterioration by ultra-violet light, or by chewing by ectoparasites. Then the birds are without physical protection, insulation and the ability to fly.

During moult, when some feathers are missing, full flight agility is impaired and birds are vulnerable to predation. Therefore they keep quiet, skulking in the undergrowth, unseen, keeping out of the way of predators as far as possible.

In some birds (especially waterfowl like the swans, geese and ducks) the loss of all the flight feathers ("primaries") occurs simultaneously, and the birds become flightless for a period.

Swan Lake: moulting swans become flightless and often aggregate into flocks during the moulting period
Masses of white feathers washed up on the shoreline is a certain indicator that moult is in progress

This mother swan is in full primary post-nuptial moult
Detail from the picture above showing the new primary feathers just starting to grow through. This bird can not fly during this process

In smaller birds, the moult is not so catastrophic and takes place over an extended period, dropping and replacing a tract of feathers in sequence. Bird ringers (banders) have a unique opportunity to observe moult and to record its progress. This gives an insight into this essential physiologically stressful process and to pin-point what factors (for example, climate change) might effect its timing and duration.

Bird-ringer Thomas rings and examines a swan

In smaller birds Primary moult can be recorded and each feather give a rating score according to whether is is old, growing or new and fully replaced.

Primary moult takes place from the "inside out".

TOP: Moult just started. The outside 7 long primary feathers are old, then two are growing.

MIDDLE, more advanced, only 4 long old feathers remain.

BOTTOM primary moult almost complete, only one unmoulted long primary at the outside remains. The next three are growing.

In real life: you can see that this Chaffinch has two long old feathers remaining on the outside, the third is shorter and is still growing. The ones inside them are new.

This male Bullfinch looks a little scruffy as he moults his plumage

A moulting Great Spotted Woodpecker


Blogger lorenzothellama said...

That is a really interesting post with brilliant pictures. I love the picture of the woodpecker.

I was taught that if you found a white feather, it means that an angel has dropped it in your path. There seems to have been a lot of angels in Cumbria recently.

Like Martin, young Thomas looks like Richard Hammond!

8:57 am  
Blogger Martin Stickland said...

I was taught lorenzybum that if you found a white feather then it would make a perfect flight for an arrow that could be used to give a Llama a pain in the backside for spreading rumors that I look like a hamster!

Nice informative post lorenzybums bro!

9:19 am  
Blogger Metamatician said...

Hello Jim! Thank you greatly for the last two comments you left on my blog recently; I feel myself the embodiment of rudeness for not having returned the favour sooner.

I've a question, obviously naive - why do birds moult exactly? Is it solely to accommodate new growth or does it function to replace worn or damaged feathers as well?

I imagine flightless birds also moult, which means that birdlike therapods at the end of the cretaceous like velocirator presumably did too. That would be quite a find in a 'page' of shale - to find a dinosaur feather all on its own.

Thanks for your insights and as always the fascinating blog which despite appearances I DO read at least once a week; I've got it not only bookmarked but on my "Quicklink" bar in Firefox so that I remember to visit the old bugger every few days to see if anything new is up.

I'm just bad at commenting. Well, not bad exactly, I suppose lazy is the unfortunate word.

Hello Lorenzo and Martin =)

2:21 pm  
Blogger Metamatician said...

By the way I have responded to both your comments on my own blog, in case that sort of information does not get emailed to you or what have you. Cheers.

2:52 pm  
Blogger lorenzothellama said...

You are not going to believe this Maalie, but I heard a cuckoo today.

6:48 pm  
Blogger Ted M. Gossard said...

Wow, Maalie. If I've ever heard of moulting before, it's long since been forgotten! I don't think I have, shamed to say! But quite interesting.

They do not seem to be as active in our yard, come to think of it, lately. But I did see a beautiful Blue Jay just the other day swoop down from our feeder and peck away inside a flower holder then crawl back up the pole with no other birds around it, unlike sparrows, who can be on this three or more at a time, then swoop up towards a nearby tree. I was surprised at this Blue Jay's size and what beautiful plummage!

5:34 am  
Blogger simon said...

What a greta post- The young fellow seems to have good control on the birds too

Well done!

6:05 am  
Blogger simon said...

great! I meant Great! not greta!

6:06 am  
Anonymous Anonymous said...

i like the photo of the goslings.

7:06 am  
Blogger Maria said...

maalie, thats really interesting, indeed!

1:00 pm  
Blogger Shrinky said...

maalie, I've learnt something new today. I had no idea swans, ducks and geese can become flightless - nor had I given much thought as to why birds must mault. A fascinating and throughly enjoyable post my friend, thank you for enlightening us.

3:28 pm  
Blogger Martin Stickland said...


You sure do know your clouds maalie!

Have a great week!

10:56 pm  
Blogger Catharina said...

Hey, I know that guy! ;-) Great post, great pictures!!

12:14 am  
Blogger Martin Stickland said...

I am such a FOOL! Of course it is a plip and not a plop!

How could I have been so stupid!

That's why I make a plopping sound whilst sitting on the lav, lets hope now that a plipping sound never occurs or I will for ever wonder what lurks down below in out waste system.

7:38 am  
Blogger lorenzothellama said...


8:49 am  
Blogger Penless Thoughts said...

I very much enjoyed this interesting, and educational, to me, post.

Thanks for your nice comment to me.

8:23 pm  
Blogger Ju's little sister said...

Maalie, as always an interesting and informative post. I won't say I never realised birds moult, because I would always pick up a stray feather on the farm. I guess more honestly I would say that I took it for granted and never gave it a second thought. But I like how careful observation can show us the process of the world around us - there is so much to learn if only we take the time to notice and the energy to reflect and deduce.

I am amongst those who did not know swans became flightless.

3:50 am  
Blogger Raelha said...

I agree with lorenzo, the picture of the woodpecker is excellent.

I was never taught about white feathers being dropped by angels, but I was taught as a child never to go near a swan as it might break my neck with one flap of its wings! That's probably why I think Thomas is ever so brave for mounting that swan.

So it's not just my neighbour's chickens that are moulting right now. I went down to buy eggs the other day and he had none to give me. I currently have to make do with shop bought ones which are inferior despite the results of your little experiment with lorenzo. My neighbour's eggs are fresher for a start, and I frequently get double yolkers. How often do you find that in shop bought eggs nowadays?

12:29 pm  
Blogger Ellee Seymour said...

Wonderful pics Maalie. I do wish you had visited me when you went to see the swans in Welney. Please let me know next time.

I think the woodpecker looks stunning.

1:17 pm  
Blogger Merisi said...

That swan looks huge!
I would bolt and run. ;-)

7:37 pm  

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