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Re: Purple Finches: Male or Female?



On Mon, 7 Feb 2000, BILL HILTON JR. (Hilton Pond Center for Piedmont Natural History) wrote:

> CarolinaBirders . . .
> 
> The thread on sexing Purple Finches (PUFI) at the feeder has been interesting.
>
[snip] 
> It's difficult to get an accurate sample of sex ratios in PUFI 
> without banding them; I'm fortunate to have that privilege, and have 
> found here at Hilton Pond that red (actually, I prefer "raspberry") 
> After-Second-Year male PUFI make up about 28% of the winter 
> population, while about 72% of them are brown, i.e., old females, 
> young females, or young males. If we make a flying leap of faith and 
> assume the M:F ratio among PUFI is roughly 1:1, we might conclude 
> that each of these three age/sex classes makes up about a third of 
> the brown birds.

What I keep wondering is why we should assume that the sex ratio is
anything close to 1:1 in the Carolinas in winter.  Many birds show
differential migration, with males wintering farther north than females,
which means that at the south end of the wintering range, most birds are
females.  Is there reason to think that Purple Finches *don't* show
differential migration?

Chris Hill
Coastal Carolina University
Conway, SC