Sal describes the houses in Bybanks as being small, identical, and arranged in a straight line, much like a row of birdhouses. This visual imagery suggests a sense of order and uniformity, which reflects the small-town atmosphere and the tight-knit community of Bybanks.
Overall, the phrase "like a row of birdhouses" is used to create a vivid mental picture of the town and its surroundings, while also conveying a sense of the town's character and the lives of its residents.