The ironic and tragic events that make up the ending of The Thorn Birds illuminate the meaning of the title of the book as well as the significance of the legend of the thorn bird described at the start of the novel.

At the end of the book, when Meggie's son Dane dies a hero's death, saving the lives of others, he is a newly ordained priest, which means that Meggie has lost yet another man she loves to the Catholic church. Her experiences with loving and losing illustrate perfectly how something, or someone, that can bring so much joy and love can also deliver heartbreak. First, Meggie loses the love of Ralph to his faith and his commitment to the Church, and then she loses their son twice: first to the priesthood and then to his own selflessness.

According to the legend of the thorn bird, great beauty is costly. Meggie Cleary's experiences with the most beautiful moments of her life cost her dearly, just as the single exquisite song of the thorn bird is possible only when its life is ending.

There are a series of events that mark the conclusion of the book.

First, Dane O'Neill, the son of Meggie O'Sullivan (née Cleary) and Ralph de Bricassart, dies in Greece. This event occurs shortly after he has been ordained as a priest in the Roman Catholic church. He drowns while attempting to rescue two women from drowning. His death has an important effect on the main protagonists. 

Cardinal Ralph de Bricassart learns that Dane was actually his son and he, too, dies (in Meggie's arms) after Dane's funeral.

The story continues with the fate of Meggie and Luke O'Neill's daughter, Justine. Justine initially ends her relationship with Rainer Hartheim because of her grief at the death of her brother, Dane. Eventually, however, they renew their relationship (after he visits her at the family estate, Drogheda) and they get married.