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Re: Heron behavior

At 09:23 PM 1/6/01 -0500, Bill Hilton wrote:

>I've seen this behavior occasionally in Great Blue Herons, and always in 
>cold weather. The legs of a heron have a lot of surface area, and since 
>they're unfeathered they radiate lots of heat. It's certainly been cold 
>enough in the Carolinas for the past few weeks to warrant tucking in one's 
>legs. :-)

On the other hand, remember that Great Blues stand in ice cold water all 
winter long, when they are actively fishing.  And water is an excellent 
heat sink, sucking the heat out of most anything it contacts.  Just ask 
anyone who has stayed in the bath tub a little too long after the water has 
cooled a bit.

Herons do have a neat physiological trick, however.  Their arteries, 
carrying the warm blood from their body, travel down the insides of those 
long, skinny legs.  Their veins, carrying the cold blood back up from their 
feet, lie along the outside surface.  But the inside arteries and the 
outside veins do lie right next to each other.  And since heat "moves" from 
hot regions to cold regions, the warm arterial blood transfers its heat to 
the cold venous blood.

Thus, all that body heat is NOT lost to the cold water outside.  Instead, 
most of it goes back up inside the main body of the heron.  In other words, 
herons are quite used to cold feet!  This system is known as a "counter 
current exchange" system, and is actually a very important way for herons 
to conserve energy.

Norman Budnitz         919-684-3592 (day)
nbudnitz@duke.edu      919-383-0553 (eve)
                        919-660-7293 (fax)

(work)	Department of Biology, Duke University
	Box 90338, Durham NC 27708-0338
(home)	4115 Garrett Drive, Durham NC 27705-8005

PROGRESS: the victory of laughter over dogma.
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