This is a fascinating account of Red Crossbill bill development. It would
be very interesting to know if other fairly closely related finch species
with crossed bill tips, such as Akepa (Loxops coccineus) and Akekee (Loxops
caeruleirostris) in the Hawaiian Islands [which have just slightly crossed
bill tips], follow a similar pattern of development.

Bob Sundstrom
ixoreus at scattercreek.com
Tenino, WA

----- Original Message -----
From: "David Beaudette" <drtbrdr at earthlink.net>
To: "Tweeters Messages" <tweeters at u.washington.edu>
Sent: Thursday, January 01, 2004 1:39 PM
Subject: Crossbill bills


> Greetings,
>
> This came through on Montana Birding today. Interesting...Any comments?
>
> Dave Beaudette
> Wenatchee,WA
> drtbrdr at earthlink.net
>
> Subject: How Crossbills get their crossed bills.
> From: Judy Hoy <bwrehab AT mtwi.net>
> Date: Thu, 1 Jan 2004 00:14:35 -0700
>
> Happy New Year mobsters,
>
> Here is an observation by Western Montana rehabers that may interest
> those of you who did not already know this.
>
>
> HOW CROSSBILLS MAKE THEIR
> BILLS CROSS
>
> I have raised several hatchling Red Crossbills and so have had
> the opportunity to observe them closely as they matured. As hatchlings,
> their bills are wide, similar to other hatchlings of the Fringillidae
> Family. As fledglings, their bills are quite cone shaped somewhat like
> a small Grosbeak bill, with the top and bottom bills coming to a point.
> The bills are nearly even in length, with the upper bill being very
> slightly longer than the lower. A fledgling Crossbill retains this
> shape and length through the period when they are following, and are
> still being fed by the parents, after fledging from the nest. During
> this time period of several days, the fledglings learn by observing the
> parent birds and each other, how to find and procure food for
> themselves.
> The fledgling birds then reach a developmental stage, at which they
> are attempting to extract pine seeds from conifer cones for themselves.
> At this time, the tips of both the top and bottom bills begin to grow
> dramatically. This appears to happen as a result of stimulation of
> certain hormones, which trigger a sudden growth spurt at the anterior
> of the ramphotheca.
> Birds in captivity have been observed in this developmental stage by
> wildlife rehabilitators to exhibit the following behavior. The birds
> select a protruding knot or the butt of a small broken branch on the
> long branches which serve as perches in the flight room in which the
> birds are kept prior to release. While the tips of the bills are
> growing, the young Crossbills twist the top bill to one side and the
> bottom bill to the other, using the selected protuberance on the branch
> to pry against. As the tips of the bills lengthen, the birds pry and
> twist several times per minute, except when they are eating or
> sleeping. Once the bird begins to pry the top bill sideways, it always
> twists the bills the same way each time. After two or three days, the
> bills are fully grown and remain crossed. The fledglings can then use
> their newly reformed bills to force open the conifer cone scales and
> hold them apart while they extract the seeds with their dexterous
> tongues. The young crossbills usually twist the mandibles in such a way
> as to cause the top bill to go to the right and the bottom bill to go
> to the left. A smaller percent twist the top bill to the left.
> This fascinating phenomena in the life of a fledgling Red or
> White-winged Crossbill does not appear to be well documented. I could
> not find this mentioned in bird behavior discussions in books or on in
> literature searches on the web. If anyone has, I would appreciate
> knowing the source.
>
> Judy Hoy_______________________________________________
> mob mailing list
> mob AT redmeadow.com
> http://siprelle.com/mailman/listinfo/mob
>
>
>