carrier pigeon
 傳信鴿


 Car·ri·er n.
 1. One who, or that which, carries or conveys; a messenger.
    The air which is but . . . a carrier of the sounds.   --Bacon.
 2. One who is employed, or makes it his business, to carry goods for others for hire; a porter; a teamster.
    The roads are crowded with carriers, laden with rich manufactures.   --Swift.
 3. Mach. That which drives or carries; as: (a) A piece which communicates to an object in a lathe the motion of the face plate; a lathe dog. (b) A spool holder or bobbin holder in a braiding machine. (c) A movable piece in magazine guns which transfers the cartridge to a position from which it can be thrust into the barrel.
 Carrier pigeon Zool., a variety of the domestic pigeon used to convey letters from a distant point to to its home.
 Carrier shell Zool., a univalve shell of the genus Phorus; -- so called because it fastens bits of stones and broken shells to its own shell, to such an extent as almost to conceal it.
 Common carrier Law. See under Common, a.

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 Hom·ing p. a. Home-returning; -- used specifically of carrier pigeons.
 Homing pigeon, any pigeon trained to return home from a distance.  Also called carrier pigeon.  Most are bred from the domestic pigeon Columba livia.  Homing pigeons are used for sending back messages or for flying races.  By carrying the birds away and releasing them at gradually increasing distances from home, they may be trained to return with more or less certainty and promptness from distances up to four or five hundred miles.  The birds typically do not stop on their way home, and may average as much as 60 miles per hour on their return trip.  If the distance is increased much beyond 400 miles, the birds are unable to cover it without stopping for a prolonged rest, and their return becomes doubtful.  The record for returnig from a distance is close to 1,200 miles.  Homing pigeons are not bred for fancy points or special colors, but for strength, speed, endurance, and intelligence or homing instinct.  Although used since ancient times, homing pigeons have been largely displaced for practical purposes by radio and electronic communications, but they are still used in some special situations at the end of the 20th century.  They were used in military operations as recently as in World War II.

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 carrier pigeon
      n : a homing pigeon used to carry messages