It may shock you to learn that poetry written during World War I was kind of a bummer. Lots and lots of people were getting blowed up very far away from home, and the people left behind were getting pretty depressed about it. Hense the sad poems full of survivor's guilt. In this particular case, Edward Thomas's character is haunted by the sad, melancholy hoots of an owl. He is, perhaps, unaware that the owl is actually an ancient spirit bent upon murder and mayhem.