Heavy-bodied, solitary, slow-moving, nocturnal rodent with quills (modified hairs) along the back, tail, and, on certain crested species, the neck and shoulders. The quills are easily detached when touched. The New World species (four genera in family Erethizontidae) are arboreal and have barbed quills; the Old World species (four genera in family Hystricidae) are terrestrial and have unbarbed quills. The North American porcupine (Erethizon dorsatum), about 31 in. (80 cm) long with a tail about 12 in. (30 cm) long and quills about 3 in. (8 cm) long, drives its powerful tail against an assailant. For food, it favours the tender tissue beneath tree bark. Crested porcupines, the typical Old World porcupines, run backward, quills erect, into the enemy. They eat roots, fruit, and other vegetation. The African crested porcupine, the largest terrestrial rodent in Europe and Africa, may weigh 60 lb (27 kg) and have quills 14 in. (35 cm) long.
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A quill pen is a writing implement made from a flight feather (preferably a primary wing-feather) of a large bird. Quills were used for writing with ink before the invention of the dip pen, metal-nibbed pens, the fountain pen, and, eventually, the ballpoint pen. The hand-cut goose quill is still used as a calligraphy tool as it provides a sharp stroke, and more flexibility than does a steel pen. The shaft of the feather acts as an ink reservoir and ink flows to the tip via capillary action.
The strongest quills come from the primary flight feathers taken from living birds in the spring. The left wing is favored by the right-handed majority of writers because the feathers curve out to the right, away from the hand holding the pen. Goose feathers are most commonly used; scarcer, more expensive swan feathers are considered premium. Depending on availability and strength of the feather, as well as quality/characteristic of the line wanted by the writer, other feathers used for quill-pen making include feathers from the crow, eagle, owl, hawk, and turkey. Often the barbs are stripped off partially or completely to allow the writer to grip the shaft more securely.