Thanks, Bob -
Bird skulls have a pretty solid braincase, but the facial portions are much
less rigid than in mammals. A majority of birds have a sort of joint where the
upper bill joins the face. Anatomically, this does not really look like a joint
in most of these, but the bones that extend from between the eyes down into the
bill are flattened in this area and quite flexible. For comparison, a 1X8"
board is a lot more flexible than a 2X4, even though they have the same
cross-sectional area. So, the bill can flex up and down, but has very little
ability for sideways movement (relative to the braincase) If you watch gulls
carefully as they feed, preen etc. you can see the angle between the bill and
forehead change quite a bit. In parrots, the amount of mobility of the upper
bill can be 30 degrees or more, and in some of them, the bones are modified
into more of a conventional joint.
All the shorebirds I am familiar with have this ability to flex the upper bill
relative to the face, and (finally getting to the dowitcher photo) some also
have flexibility and musculature to flex the bill out closer to the tip. To
understand this, it helps to understand a little of the structure of bird
bills: Bills consist of a bony core with a little soft tissue around it (mainly
blood vessels and nerves) surrounded by a keratinized sheath (keratin is a
major component of fingernails, cow horns, etc.). The hardness and rigidity of
the sheaths vary a lot between birds, just as fingernails are softer than cow
horns. Raptors, parrots, herons, storks, hornbills, and toucans, for example,
have very thick, durable, and rigid keratin. On sparrows and finches, it is a
lot thicker and harder than on thrushes and smaller flycatchers - adapted to
their diets.
Among shorebirds, the thickness and hardness is highly variable. It is quite
hard in Oystercatchers, much less so in longer-billed species that probe in
soft mud. Species like dowitchers and snipe have a sheath that is less
keratinized, more like leathery skin. They also have more soft tissue between
the bone core and the sheath, including a little muscle and a lot more nerves.
And, some have the ability to flex the tips quite a bit, as in the dowitcher
photo. This happens partly because the bone is thin and somewhat flexible, and
because the sheath has some capability to move relative to the bone - like the
fingertip of a loose glove.
Hope this helps -
Wayne
From: "Bob Archer" <rabican1@xxxxxxxxx>
To: "obol" <obol@xxxxxxxxxxxxx>
Sent: Monday, February 29, 2016 7:34:14 AM
Subject: [obol] Re: Shorebird Bill Flex
Hi:
Bill length is not a factor, from what I understand "most" shorebirds and their
relatives "Charadriformes" have this ability. Many of the bills we see as hard
sticks or shovels are actually very flexible tools. I do not know the exact
evolutionary development of bills ( I do know it is fascinating) , but the
shorebirds are well equipped to quickly grasp food sources or filter feed. This
is a topic for a Wayne or Joel to explain to us :).
Bob Archer
pdx
On Sun, Feb 28, 2016 at 10:38 PM, Priscilla Sokolowski < priscillanhk@xxxxxxxxx
wrote:
