1882 15 Feb. 175 ‘Sib breed’..is a word used in the North for the particular kind of canary employed for mule breeding, and really means that the birds have been bred in-and-in for a number of years.
1987 E. W. Burr vi. 33/1 Mule breeding, the production of sterile hybrids involving the canary and various finches, is very popular in Europe.