[CT Birds] Ducks and stuff...

[Dennis Varza]

Dave pretty well lays out the Big Picture of migration but doesn't  
lay out the micro-behavior too well, which I don't think anybody  
really knows.

I read a paper on wintering Bald Eagles where they commented that  
birds from Maine can fly down to Long Island and back in one day. Who  
says that birds migrating north do not retreat when prudent,  
especially waterfowl that need open water. I wouldn't be surprised  
that eager ducks fly inland looking for open water and not finding it  
return to the coast. Locally, when reservoirs are freezing and  
thawing, one can see an increase in birds on the coast when they freeze.


That is the way I see it

Dennis



On Mar 12, 2008, at 1:46 PM, David.F.Provencher at dom.com wrote:

>
> Paul,
>
> Here is a very brief response to the question of duck migration  
> timing, as
> I understand it. There are several possible triggers for duck  
> migration. It
> is believed length of daylight, or angle of the sun relative to the  
> earth,
> triggers hormonal changes which in turn cause restlessness in the   
> birds
> and then actual migration. With waterfowl there have also been  
> cases where
> mass migration days seem to have been triggered by particularly foul
> weather (plenty of scope for puns there). So it isn't a case of the  
> birds
> knowing when to go or knowing what conditions are like on the  
> migration
> route or at the ultimate destination but rather mostly instinctual  
> behavior
> triggered by environmental stimulus. Of course the timing of  
> migration can
> be modified over time by changing conditions. If a species migrates  
> over a
> period of weeks and conditions change such that the early migrants  
> meet a
> high mortality rate, for instance iced in wetlands as you  
> mentioned, then
> the remaining breeders who arrive a bit later when conditions have  
> improved
> will generate a new generation of birds that tend to migrate a little
> later. If on the other hand the early migrants meet a favorable  
> environment
> on arrival, they will have taken all the prime breeding sites and  
> will tend
> to be more successful than later arriving birds. This will bias the
> migration period slightly earlier. The whole migration thing is truly
> fascinating isn't it? And insect migration is even more intriguing.
>
> Dave
>
>
>
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