Complex sentence: Having other parakeets encourages a pair to breed, which is why breeding in groups is more successful, however many breeders choose to breed in pairs to avoid conflicts and because that way they know for sure which parents produced any given birds.
Split into simpler sentences: Having other parakeets encourages a pair to breed, which is why breeding in groups is more successful. However, many breeders choose to breed in pairs because that way they know which parents produced any given birds.