The bird was discovered by a bus driver on a 102 Stagecoach service from Edinburgh to Dumfries on Wednesday at about 5.20pm when the vehicle arrived at its destination.
The pigeon, which has brown and white feathers, was not tagged and the Scottish SPCA is now trying to locate its owner in the hope it was not deliberately abandoned.
Animal rescue officer Sheena MacTaggart said the bird will be looked after at one of the organisation’s rehoming centres until its rightful owner has been found.
She said: "The pigeon, which has distinctive white and brown plumage, was discovered in a homemade wooden box with a blue handle.
"Unfortunately the bird doesn't have any rings we could use to identify an owner.
"We're hoping that this is just a case of someone being a bit forgetful, rather than anything intentional, and we can reunite this pigeon with the rightful owner as soon as possible.
"In the meantime, the bird will be cared for at one of our animal rescue and rehoming centres."
Anyone with information can contact Scottish SPCA on 03000 999 999.
The Scottish SPCA is Scotland’s animal welfare charity. The organisation is separate from the RSPCA, which works in England and Wales.
The charity receives no government funding and is the only animal charity in the UK able to report animal cruelty cases to the Crown, with reports sent to the Crown Office Procurator Fiscal Service.