Staying on the freezing theme, this winter’s BTO Bird Table magazine contained an interesting article by Mike Toms on how bird survive cold winter nights. Communal roosting is a strategy I’m familiar with, as is birds finding holes in which to hide. I clearly remember when working in a country park in Coventry finding a treecreeper roosting head first in shallow crevice in a stately old redwood, the only sign of its presence being a trail of droppings.

What I didn’t realise was that some birds can actively reduce their body temperature to induce a condition known as controlled hypothermia.

Birds have a body temperature of 40 degrees C give or take a couple of degrees. Lowering this temperature results in less fat burned, reserves last longer and better chances of surviving the night. Willow tits for instance have been found to be able to reduce their temperature by 6 degrees resulting in a 10-15% energy saving.

This process is distinct from induced torpor and hibernation proper, as it doesn’t involve huge drops in temperature, just enough to increase survival. The ability to massively reduce temperature is best known from hummingbirds and from the remarkable discovery in the late 1940s of an apparently hibernating poorwill in the Colorado Desert. Subsequent investigations of this relative to our nightjar revealed that it induced a drop in temperature to a mere 18-20 degrees C. It is suggested that this can enable the birds to survive up to 100 days on normal fat reserves, a pretty good way to survive cold weather.

Additional Note: Good article on torpor in hummingbirds here


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  • About

    In this blog we'll describe the day to day comings and goings of the birds in our Devon garden.
  • About us

    Tony is a naturalist and environmental artist. Laura is a free range creative web and print designer. We've recently moved from the village of Ipplepen to the town of Newton Abbot with our two children Ralph and Oli, our dog Henry, and numerous cats (none of whom would ever dream of eating birds).
  • Species List

    List of species, including only those birds that land in the garden:
    Blue tit
    Carrion Crow
    Chiff chaff
    Coal tit
    Collared dove
    Great spotted woodpecker
    Great tit
    House Sparrow
    Long tailed tit
    Mistle thrush
    Pied wagtail
    Song thrush
    Wood pigeon

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