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Re: love in the air



At 04:20 PM 2/14/01 -0500, you wrote:
>And speaking of love in the air, just four days ago (February 11) I
>heard my first Pine Warbler of the year singing from a Loblolly Pine.
>I wonder if the last three days hushed it up again. Does anyone know
>if birds will be fooled by warm spells and start singing unseasonally
>early, or if their internal clock makes them difficult to fool?

I suspect that for most of our winter songbird species, photoperiod is the 
more important factor in changes in hormone production.  As day length 
increases, hormones involved in breeding physiology kick into 
production.  Testicular and ovarian tissues that had withered away to 
practically nothing last fall begin to grow again.  (Why carry around all 
that extra weight in the off season when you don't need it!)

These same hormones also affect breeding behavior.  I suspect that warm 
days just prompt (or release) the expression of that behavior.  On cold 
days, these breeding *urges* (whatever that means) may be suppressed in 
favor of the more important tasks of finding and eating enough calories to 
keep the life fires burning.

As Josh Rose has pointed out, here in the Carolinas, we can hear Pine 
Warblers singing on any given winter day, if the temperature is up and the 
sun is shining brightly.  Nice!

It's also worth noting that the songs we hear on these early warm days from 
birds like White-throated Sparrows are not *full* songs.  It's as if the 
birds themselves are *warming up,*  practicing their songs for the big 
effort that's ahead on the breeding grounds.  Some of you might remember 
the discussions last spring about Hermit Thrushes and Fox Sparrows being 
heard throughout the Carolinas.  This doesn't mean that they will be 
breeding here.  They're just tuning up.

But it won't be long now!

Norm
***********************************************
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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