[CT Birds] waterfowl sex ratios

Chris Elphick elphick at sbcglobal.net
Fri Mar 9 06:30:09 EST 2012

A couple of people have asked about why they are seeing many more male 
ring-necked ducks than females (apologies if someone has already answered - I've 
not been able to track everything on the list very closely the past couple of 
weeks). I don't know the specific answer for ring-neckeds, but for migratory 
birds in general it is quite common for males and females to winter in somewhat 
different places.  The separation is rarely absolute and the most common type of 
separation is along latitudinal lines.  

In songbirds, what usually happens is that males tend to winter farther north 
than females, such that at the north end of the winter range there is a bias 
towards males, while at the south end of the winter range the reverse is true.  
A common explanation is that there are two contrasting forces at play.  In 
general it is better to be farther south, because then it is warmer, there is 
more food, etc.  But, if you are male and need to get back to the breeding 
grounds early to get a good territory -- and earlier arrivals often do have an 
advantage, then you're better off wintering close to the breeding grounds as 
that makes it easier to get back early - this is also why male warblers show up 
before females in spring.  So, for males there is a trade-off that means they 
don't go any farther than they absolutely have to.  For females there is not as 
much of a trade-off (because females in most songbirds do not defend 
territories), so they can afford to go farther south and be sure they are 
well-off over the winter.

Returning to ducks, I'm not sure how well the above explanation works because 
ducks have a very different breeding system compared to songbirds (males and 
females tend to pair up before getting to breeding sites, with males following 
females back to breeding areas - so there isn't the same pressure to get to 
territories).  If I get a chance, I'll dig around in the literature and see if 
there are waterfowl-specific ideas out there.


 Chris Elphick
Storrs, CT
elphick at sbcglobal.net

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