[wisb] Re: Bird Feet RFI
- From: "wildlightphoto@xxxxxxxxxxxxx" <wildlightphoto@xxxxxxxxxxxxx>
- To: wisbirdn@xxxxxxxxxxxxx
- Date: Wed, 9 Feb 2011 10:31:46 -0500
Countercurrent exchange doesn't allow the blood to remain warmer throughout
the leg (the referenced diagram shows this) but by transferring the warmth
of the blood flowing to the feet to the blood returning to the body core,
net heat loss is minimized. Without the countercurrent heat exchange the
delta T at the feet would be higher and heat loss would be greater.
Doug Herr (mechanical engineer)
Orangevale, Sacramento County
http://www.wildlightphoto.com
Original Message:
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From: Erik Bruhnke birdfedr@xxxxxxxxx
Date: Wed, 9 Feb 2011 08:56:13 -0600
To: manderson@xxxxxxx, wisbirdn@xxxxxxxxxxxxx
Subject: [wisb] Re: Bird Feet RFI
Marge,
I meant to send this earlier, but didn't get around to it. Scott is totally
correct. The term that I learned when I took ornithology a few years ago was
"countercurrent exchange," which is basically having the temperature of the
blood stay relatively constant as the blood moves through most of the leg.
Here is the thing... in people, the blood in our extremities flows to the
tips/outermost portions of the extremities (via arteries), then flows back
to our core (via veins). Birds have this ability to transfer warmth from the
arteries (as the blood moves throughout the leg) to the veins in the leg
(the returning portion of blood). By doing so, the blood remains warmer
throughout the leg longer, and it creates a more average blood temperature
from upper leg to foot... whereas with people, it's all warm, eventually
turning all cold because of the lack of heat-sharing. Here is a diagram I
found online. Think of the two orange columns as arteries (left) and veins
(right), with the numbers describing the transfer of heat.
http://www.knowledgerush.com/wiki_image/c/c2/Countercurrent_exchange.png
Hope this makes sense. Good birdwatching,
Erik Bruhnke
Duluth, MN
NATURALLY AVIAN - Bird photography and guided birdwatching tours
www.pbase.com/birdfedr
www.naturallyavian.blogspot.com
birdfedr@xxxxxxxxx
On Tue, Feb 8, 2011 at 3:11 PM, Marge Anderson <manderson@xxxxxxx> wrote:
> Hello WisBirders:
> I read somewhere that there is something about bird legs/feet that makes
> them able to tolerate the cold with their feet exposed. Now I can't
> remember what it was or where I read it. This topic came up in our office
> kitchen between me and a colleague who is raising urban chickens. I said
I
> thought there would be many WisBirdnetters who would know the answer to
> this, and since our email traffic is low in this pre-migration period, it
> was a good time to toss it out there.
>
> Marge Anderson
> Dane (and Vilas) County
>
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