Thus, courtship is the visible part of a complex series of events whereby the males and females come together for mating. The continuation of pair-bonding after mating is common in birds and mammals because the survival of their genes depends on the fertilized eggs reaching maturity. If that requires support from "both" parents, the rituals are the way the pair keep connected. Established pairs, even in the Great Crested Grebe, will live as singles (often in a large group) outside the mating season.