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The Crossbill is the Loxia genus
of birds which is part of the Fringillidae
(FINCH) family.
The name comes from the unusual quality that they have, whereby the horny
sheaths of the upper and lower part of the bill cross each other slantwise
(this peculiarity has, however, been many times observed as a deformity
in other groups of birds, and especially in Crows.
Such cases may be well compared to the anomaly often seen in Rabbits wherein
the front teeth reach an disproportionate size). This slanted crossing
of the bill also inspired the scientific name Loxia, derived from the greek
loksos meaning oblique, which was given to this genus of birds by Gesner
and carried on by Linnaeus.
When first seen, the crossed bill almost looks
like a physical defect or mutation similar to that mentioned above in rabbits.
Ornitholigists and writers in the past have often referred to the bill
is this manner. The special animosity of De Buffon on this point
may perhaps be explained by the existence of a mediaeval legend (of which,
however, be it said, he takes no notice), best known to English readers
by Longfellow's pretty version of Mosen's poem, to the effect that the
bird acquired its peculiarly shaped bill and colour of its feathers in
recognition of the pity it bestowed on the suffering Jesus at the crucifixion,
and the Crossbill's attempts to pull the nails from the cross, resulting in Jesus' blood spurting out over the bird's breast and staining it for all time. Schwenckfeld
in 1603 (Theriotropheum Silesiae,
pp. 253, 254) gave the fable in
the Latin verses of Johannes Major, which have been reprinted in Notes
and Queries (series 5, vii. page 505)).
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Rather than a defect though, the crossed bill is
a wonderful adaption to the habits of these birds. This design makes
it possible for the seeds of fir cones from coniferous trees to be picked
out with very little difficulty. These seeds represent the Crossbill's
main food although apple pips are also a favoured treat. These birds
will also feed happily on insects and other fruit seeds in the winter,
at which time they will travel in any direction on the compass to visit
deciduous forests, gardens, flat plains and groves in search of food.
It appears that the first description of the Crossbill's
method of using its bill was by Townson in 1799 in his book "Tracts on
Natural History", although the account was quite concise. A
more detailled explanation was provided by Yarrell in 1829 (Zoological
Journal, pages 459 to 465), in which he described how the muscles and jaws
are so masterfully capable of tearing apart cones, or fruit like apples.
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The moveable joint between the quadrate bone and
the mandible enables a large amount of sideways movement. With the
special way in which this bird's muscles move the mandible, as soon as
the Crossbill opens its beak the mandible's point becomes located directly
opposite the point of the maxilla. The bird then inserts its bill
into the fir cone or in the fleshy fruit, and then opens its bill a little
further. This additional widening of the bill, and a forceful sideways
movement of the mandible whilst inside the fir cone or fruit results in
the seed being torn away. Then, just at the right time, the tongue
shoots out to obtain the seed, and almost as soon as the tongue has darted
out, it is quickly retracted into the Crossbill's mouth with the treasured
seed itself.
The breeding season for the Crossbill seems to
be more variable than other small birds, but normally eggs are laid at
the end of February or beginning of March. The nest is large and
rougly-made of of spruce sticks and lichen, and is built in the coniferous
trees which form the bird's main habitat. Around four eggs are normally
laid, which are similar in appearance to, but bigger than, those of the
GREENFINCH.
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