I like the idea of following the bird around with a pooper-scooper and
sending the results to Sam's Fecal Hormones R Us Lab, at the WPZ -- but
unfortunately, at this time of year both sexes would probably have
undetectable levels of hormones. Okay, then, plan 2 is to ring the pond
with Potter traps until we can get the bird in the hand and really get a
GOOD look. Then we can pull a feather, hold it in a cage for a week till
a new feather starts to grow in, pull THAT blood feather and send it to a
lab for DNA testing. Or well, hell, just lap it right there in the Fill.
Forget just enjoying the bird! I want to know what sex it is! Confess,
confess, little longspur...

A couple last comments: Just FYI, the area of solid black that I observed
when the bird "stood up" was not on the breast (I agree the breast was
barred), but lower down, on the belly. This is the area that would be
between the bird's legs when it is walking normally. Dennis's comment
that stretched-up birds will show more of their feather bases is a good
point -- that could change a "buffy" breast to a "barred" breast -- but
it still looked like there was a solid patch lower down.

And, it's interesting to hear that breeding females can have lots of black
on them -- but how about wintering females? Given that chestnut-coloreds
do so much feather wear, it is essential to be comparing winter birds to
winter birds, and breeding birds to breeding birds, yes?

Looking into my crystal ball, I sense a trip to the Burke Museum (and to the
Montlake Fill again) in my near future...