The Black Robin, a species whose entire population, was once down to 5 individuals (and only one fertile female) now number 250 birds. All these birds are descendant of the female bird "Blue" (later known as Old Blue). This inbreeding doesn't seem to have caused any negative effects. Possibly serious population reductions in thr past have causes all harmful alleles lo be lost.
The kakapo aren't so lucky. The male kakapo have been sorted into Studs and Duds. The Studs with the good sperm are sharing an island with the females, while the Duds are all on another island.