Date: 3/20/17 8:33 am
From: Geo Kloppel <geokloppel...>
Subject: Re: [cayugabirds-l] Migration Video and question
Hi Pete,

It's a global cycle, so the farther one goes from the equator in _either_ direction the greater the amplitude becomes. That just increases the salience of the cycling rate of change in photoperiod for any migrants that completely transit the tropics to spend our winter in the temperate or higher south latitudes.

-Geo

On Mar 20, 2017, at 10:50 AM, Peter <psaracin...> wrote:

> Thanks Geo.
>
> How about migrants wintering deeper into So. America?
>
> Pete

-Geo

Sent from my iPhone

> On Mar 20, 2017, at 10:50 AM, Peter <psaracin...> wrote:
>
> Thanks Geo.
>
> How about migrants wintering deeper into So. America?
>
> Pete
>
>
>> On 3/20/2017 9:52 AM, Geo Kloppel wrote:
>> Colombia, Venezuela, the Guyanas, and northernmost parts of Brazil and Ecuador actually lie in the northern hemisphere, where days have been lengthening ever since our winter solstice. Right now (at equinox) the rate of photoperiod change has reached its maximum, noticeable even in equatorial regions. I presume that seasonal migrants are sensitive to that rate, which has been accelerating ever since December 21st, reaches its peak today and now begins decelerating toward the next (our summer) solstice. The amplitude of the cycling rate of change is subdued in the tropics, but it's the very same cycle that is so pronounced in the higher latitudes where these warblers breed each year, so I doubt that they lose track of it, even if they winter at or south of the equator, as some do.
>>
>> -Geo Kloppel
>>
>>> On Mar 20, 2017, at 8:22 AM, Peter <psaracin...> wrote:
>>>
>>> Folks.......I have a spring migration question and wonder if anyone out there can help. I understand that the lengthening days ignites hormonal responses in birds and, among other things, encourages "migratory restlessness" - an "itch" to begin their respective journeys north. But how does this mechanism work with respect to neo-tropical warblers? After all, for those spending their "winters" in northern So. America the days will be shortening!!! The "photoperiod" will be decreasing.
>>>
>>> What, then, is the trigger to get them on the move and heading northward?
>>> Thanks for the help.
>>>
>>> Pete Saracino
>>
>> -----
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 2016.0.8007 / Virus Database: 4756/14149 - Release Date: 03/20/17
>

--

Cayugabirds-L List Info:
http://www.NortheastBirding.com/CayugabirdsWELCOME
http://www.NortheastBirding.com/CayugabirdsRULES
http://www.NortheastBirding.com/CayugabirdsSubscribeConfigurationLeave.htm

ARCHIVES:
1) http://www.mail-archive.com/<cayugabirds-l...>/maillist.html
2) http://www.surfbirds.com/birdingmail/Group/Cayugabirds
3) http://birdingonthe.net/mailinglists/CAYU.html

Please submit your observations to eBird:
http://ebird.org/content/ebird/

--
 
Join us on Facebook!