When the Birds Fly South is considered by numerous critics to be Coblentz’s best fantasy novel. Written during the middle of his career, this novel has several fascinating aspects. Coblentz weaves a mysterious atmosphere around the Valley of Sobul that remains even at the end of the novel. He explores the tragedy of a doomed romance and the foolish stubbornness that leads a man to destroy everything he loves.
An aura of mystery surrounds the Ibandru and the Valley of Sobul. The Ibandru’s mysterious disappearance in the winter, their equally strange reappearance in the spring, and a prophecy that promises doom when a stranger appears in the valley all contribute to this aura. Coblentz drops hints that the Ibandru transform themselves into birds, but he never confirms it. Dan Prescott never sees the transformation, leaving the possibility that there might be another explanation. Yasma’s death seems to confirm the supernatural aura surrounding the Ibandru, but Dan never actually sees her change into a bird. Similarly, the statue of Yulada appears to be only a rock formation, but the goddess still seems to exhibit power when Yasma slowly withers away following disobedience to the will of the deity. Coblentz provides no answers concerning the power of Yulada, leaving readers to decide for themselves.
One of the strongest aspects of Coblentz’s novel is the tragic relationship between Yasma and Dan. Readers know from the foreshadowing in Dan’s narrative that the relationship is doomed. The most tragic aspect of this romance is the fact that Dan is directly responsible for its destruction. The burning desire to understand the unknown that led Dan to the Valley of Sobul turns against him in his relationship with Yasma. He refuses to stop seeking answers to the mysteries that surround Yasma and the Ibandru. Although it is understandable that he does not want to be separated from his wife for the entire winter, it seems foolish for him to ignore her pleas because he firmly believes that she is only being superstitious. If he would not have been so stubborn in pursuing the answers to his questions and forcing Yasma to stay with him, she might not have died, and they could have stayed together. It is only shortly before Yasma’s death that Dan learns that his single-mindedness was responsible for the tragic end of their marriage.