Board Thread:Questions and Answers/@comment-36855838-20181121131041/@comment-27950421-20181121134317

KC hasn't given that information as of yet, but we do know that harpies at least do lay eggs.

All mamono who are derived from egg laying creatures are assumed to lay eggs themselves. The number of eggs laid is assumed to be similar in a clutch to be a similar number to the number of children a human woman gestates in a single pregnancy. When the egg hatches the offspring is physically developed to the point of equalling a human toddler and either rapidly mature psychologically to the same level or is born at that same level of mental maturity.