Explaining the Blue
THIS POST on a curiously ‘blue-capped Bittern’ (blue-grey on crown and in malars and even little at the bill base) at Buckton Pond produced highly illuminating responses. So here, a follow -up bringing those comments together. Certainly new learning for me (MG). James McCallum and Norman McCanch brought the intel. Robbe added a photo of a similar bird.
“I’ve seen a couple of wintering Bitterns that appeared similar to this. In addition one memorable observation concerned a ‘text book plumaged-bird’ which, having spent several minutes preening under one wing, raised a very floury head – presumably covered in powder down. It was reminiscent of the bird you’ve photographed here and perhaps provides an explanation?
Powder Down – I looked this up shortly after observing it and was amazed to find out just what happens. Anyhow if my memory serves me this is basically what I read – perhaps somebody else will explain it more clearly –
Bitterns + Herons and some other bird species have patches on their bodies where this powder down is produced. I think that these are patches of specialised down feathers that are not moulted and grow continuously and disintegrate at their tips to form fine powder. Bitterns have two pairs on the breast sides and thighs and these presumably help the birds clean themselves from fish slime…etc. The Bittern I saw ‘powdering’ itself looked rather similar to your photos and it remained looking like this for an hour or so until I lost sight of it in the reeds. Of course if the bird you saw continues to look like this throughout the day then you can quickly dismiss the idea – It was just a thought!
(Found a dead Little Egret and it was quite easy to locate them – they looked quite horrible but are clearly useful!)
I also found some sketches of two different wintering Bitterns which both have dull grey-blue crowns, I’d put these down as young birds but am not 100%
I found the subject fascinating – connected and equally interesting is the preening comb present on the inner edge of the middle toe. I once found a dead Bittern and was amazed to see theses beautifully formed combs – I really like these adaptations but they are frustratingly hard to see in the field.”
from Norman McCanch:
Attached a photo of the powder down patches on a dead bittern found in bizarre circumstances on my local patch in Kent last year. There seem to be rather few images of these structures out there, so thought it might be of interest.
At Seaton Lakes (my patch near Canterbury) I often get the chance to watch Bitterns undisturbed for extended periods and the bluey grey dusting can sometimes be seen during and shortly after preening. The purpose of the dust is to coagulate fish slime on the feathers, so it can be raked off using the adapted pectinate claws. It seems to get most frequent use if Bitterns catch eels, for obvious reasons.
Not your usual bird picture, but it might be of some interest.
“This Bittern I photographed in Belgium on Feb 8th has ‘powder’ even on the base of the bill.” Click here to see.