RE: [SBB] Common Poorwill at Almaden Quicksilver

["Alvaro Jaramillo" <[[email protected]]>]

Les et al. 

   The word hibernation has a very specific meaning; at least that is how I
was taught the term. For an animal to hibernate it has to slow down its
metabolic rate and allow its body temperature to decrease to the ambient
temperature. To "wake up" from hibernation for warm blooded animals is very
difficult and energy consumptive, usually involving special fat tissue
(brown fat) that is very efficient at creating heat. An animal that comes
out of hibernation uses enough of its brown fat stores in the process that
it may not be able to undergo the process again until it replenishes its fat
stores. Many mountain ground squirrels undergo true hibernation, the
Poorwill undergoes true hibernation, but bears do not. Torpor is more
loosely defined, it is a moderate or substantial decrease in metabolic rate
and body temperature, how much of a decrease you can argue about. It is not
that difficult to wake up from torpor. Torpor is like you turn down the
furnace, hibernation is that you turn it off (but leave the pilot light on).


As far as I know lots of birds use torpor in their lives, some Andean
hummingbirds, like the Andean Hillstar do it every night. Many nightjars use
it, and some group roosting little passerines use it to some extent.
However, the dogma at least is that the only bird which has been confirmed
to hibernate is the Poorwill. They don't do it for the entire winter, but
for stretches of several days or weeks from what I understand, but I could
be wrong on this. 

Regards

Al

Alvaro Jaramillo
[[email protected]]
Half Moon Bay, CA

Field Guides - Birding Tours Worldwide
http://www.fieldguides.com/home.htm


> -----Original Message-----
> From: south-bay-birds-bounces+chucao=[[email protected]]
> [mailto:south-bay-birds-bounces+chucao=[[email protected]]] On
> Behalf Of Les Chibana
> Sent: Saturday, June 18, 2005 12:56 PM
> To: South Bay Birders
> Subject: Re: [SBB] Common Poorwill at Almaden Quicksilver
> 
> David,
> 
> If you are asking if they spend the winter in a state of torpor, Common
> Poorwill (COPO) don't appear to do so. They are capable of lowering
> their metabolism to a very low level (torpor) during times of low
> temperature. Hummingbirds do this as well. Birds can be in torpor
> overnight and maybe a bit longer. Hibernation often refers to spending
> the whole winter in torpor, as exhibited by high latitude bears during
> winter. But a secondary definition makes it about the same as torpor,
> with no indication of a long time period. The Birds of North America
> (BNA) account doesn't say that poorwill hibernate. In Kenn Kaufman's
> "Lives of North American Birds", he uses hibernation in quotes. In the
> Sibley Guide to Bird Life and Behavior, Robert Behrstock notes that
> there are reports of COPO going into extended periods of torpor through
> winter, but doesn't use "hibernate". In the John Terres Encyclopedia of
> North American birds, hibernation is used without quotes. The first
> three references are more recent than the last.
> 
> If there is another question/assumption here, i.e., does this mean that
> they are present year-round, the answer is, probably not. It depends on
> which reference you use. The BNA account shows our area a little
> outside their year-round range. The National Geographic Reference Atlas
> to the Birds of North America, edited by Mel Baughman, indicates that
> our area is at the edge of their year-round range. Their seasonal
> movement, or presence, is not very well understood. If there was a
> significant number (are there any?) of records of their presence in
> winter locally, we might more easily accept that they are present
> year-round and are just undetectable during winter in this area. Such
> is the case for many nocturnal, cryptically-marked species.
> 
> Les
> ---
> Les Chibana
> BirdNUTZ(tm) - Ornigasmic Birding
> em <[[email protected]]>
> web <http://www.birdnutz.com>
> ph 650-949-4335
> fx 650-949-4137
> snailmail: SR2 Box 335, La Honda CA 94020
> 
> On Jun 18, 2005, at 11:33 AM, David Forthoffer wrote:
> 
> > At 06:54 PM 6/17/2005, [[email protected]] wrote:
> >> we also  saw two COMMON POORWILLS ...
> >
> > Those birds hibernate when it is very cold, right?
> >
> > David Forthoffer
> >
> 
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