As a result of restrictive receptivity of females and their rare and scattered distribution plus the high cost of searching, it is probably better for a male to stay with one female for several breeding episodes and guard her, ensuring his paternity and also helping to defend the anemone, the female, and his young that she is carrying. As in many monogamous systems, the male will mate with another female should she be available. However, the female would drive her off. Birds offer many examples of monogamy. Mate guarding plays a role in male giving up opportunity to search for other receptive females, but other factors are also involved.
Males can provide care to female while courting and brooding and to young.
This enhances female fecundity and survivorship of the young and thus directly impacts on the male's fitness. This promotes male care to provide sufficient food. Precocial birds can grow more slowly and don't require as much input from males. Monogamy is rarer in precocial birds. Ecological conditions often dictate that breeding is rather synchronous in birds.