Garuy,

According to BNA:
Bill distinctive, with mandibles curved and crossing at tip. Lower
mandible crosses to right as often as to left.


Scott Ramos
Seattle



----------------------------------------
From: "Gary Bletsch" <garybletsch at yahoo.com>
Sent: Monday, March 23, 2015 9:00 PM
To: "Tweeters Tweeters" <tweeters at u.washington.edu>
Subject: [Tweeters] crossbill question
Dear Tweeters,

It occurred to me today that I did not know the direction of the curvature
of the bill of a crossbill. I looked at some pictures on the Internet, and
saw some variation. With these images, I figured there might be some photos
that had been reversed according to the photographer's whim, perhaps.

The pictures in my copy of Big Sibley show the top mandible going to the
bird's right, in both of our species of crossbills.

The pictures in Lars Jonsson's Birds of Europe with North Africa and the
Middle East appear to show the top mandible going to the left on a male Red
Crossbill, but the top mandible going to the right on the female. This book
shows a male Parrot Crossbill with the top mandible going to the right,
with the female's top mandible going left. Then it shows the White-winged
Crossbill female's top mandible going right. I couldn't tell what Jonsson
was showing on the male White-wing, because the bird is depicted with bill
open, attacking a cone.

I had always assumed that crossbills had the same sort of chirality as
that seen in the various species of flatfishes, where the "handedness" was
always the same in a given species, barring rare mutations.

How does this work in crossbills?

Yours truly,

Gary Bletsch


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