Even in the same sub-breed, as in that of the short-faced tumbler, it is notoriously difficult to breed nearly perfect birds, many departing widely from the standard.
Azpiarraza berean ere, itzulipurdikari aurpegimotzean bezala, zailtasun nabaria dago banako hobezin samarrak hazteko, asko baitira standardetik urrun aldentzen direnak.