The Roller Canaries in contests are trained to sing when the covers are removed from the contest cages. They are placed in these cages when they have finished the moult, and the covers are then gradually applied over a period of one week.
When they are closed fully you can either introduce a Tutor bird or play a tape of the song. The covers are withdrawn during the day for periods of five to ten minutes for the bird to sing. The birds can then be rewarded and the covers reapplied.
The idea is to get them used to singing in different locations with the set time (usually five to seven minutes) as if you were in a contest.