What does the heron symbolize in "Night Calls" by Lisa Fugard?

The heron symbolizes both hope and the transient nature of life.

In the story, Marlene's mother dies in a car accident before Marlene turns eight. The loss is devastating to Marlene, as her mother had been both her beloved parent and tutor. At the time, Marlene's father had wanted to leave the sanctuary altogether; it was too painful to continue living there.

However, in due time, a red-crested night heron is brought to the sanctuary; the National Parks Board wants the heron to be kept at Modder River until a mate can be found for it. So, Marlene is sent to boarding school, while her father tends to the heron's welfare. During school vacations, Marlene returns to the Modder River Wildlife Sanctuary to visit her father. As the warden of the sanctuary, Marlene's father is responsible for all the animals there. Marlene notices that, as time progresses, her father becomes almost enthusiastic about life. Here, the heron symbolizes hope to Marlene and her father; it represents healing and a new beginning.

During the holidays, Marlene's father shares with her the latest news about the heron. He even shows her the South African 37-cent stamp bearing the heron's image. For a time, the bird becomes the chief attraction at the wildlife sanctuary. Visitors come, and Marlene's father chats with them about the bird. Eventually, however, public interest evaporates, as the prospect of finding a mate for the heron diminishes.

In the end, Marlene's father decides to release the heron back to the wild; however, he neglects to tell the truth to Marlene and instead, explains that a hyena had probably gotten the best of the heron. Marlene never lets on that she had witnessed him taking the heron down to the river one night. It remains a cherished secret between them. Each evening, both father and daughter privately savor listening to the heron's night calls.

Yet, as fate will have it, the heron dies, presumably because it was attacked by a wild animal. With the death of the heron, the night calls stop, reinforcing the notion of the heron as a symbol of ephemeral (transient) life. For a time, the heron gives hope to Marlene's father, and he finds a purpose in caring for it. However, in returning it to the wild, he also delivers the heron to the whims of nature.

Its fate mirrors that of his wife's fate; both the heron and his wife are subject to events beyond their power to control. So, the heron symbolizes initial hope and new beginnings for Marlene and her father, but it also represents the transient nature of life when it succumbs to nature's demands.