birding-aus birds and cold feet

Subject: birding-aus birds and cold feet
From: "Wim Vader" <>
Date: Tue, 09 Mar 1999 10:12:08 +0100

        Why don't birds sitting on snow or ice (or Cockies on metal perches) get
cold feet, asks Anne Green? I don't know about the cockies, but birds who
habitually live in cold environments havefound a neat solution for this
problem.Most of the work I have seen has been on gulls, but I guess the
mechanism is used by other birds as well.
        Birds can control the blood flow through their legs to an amazing 
and when they stand on a cold surface, they can reduce the blood-flow with
up to 90%. This they do by constricting the arteries in the feet and
opening up a shunt above the feet, allowing \most of the blood to circulate
through it. In addition, the birds have an arrangement by which the cooled
blood flowing back from the feet is warmed up by the arterial blood going
into the feet, while the arterial blood is cooled down, thus further
conserving body heat. (Conversely, birds can also get rid of excess heat
through their feet).
        I hope that this was sufficiently non-technical. Not being a 
myself, I can not give you the technical details anyway.

                                                Wim Vader, Tromsø Museum
                                                9037 Tromsø, Norway

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