American Scientist

In his most recent book, The Nesting Season: Cuckoos, Cuckolds, and the Invention of Monogamy (The Belknap Press, $29.95), biologist Bernd Heinrich explores the mating and parenting repertoires of birds, interweaving his own observations with some of the latest and most fascinating scientific findings. The book opens with a captivating account of his attempts to parent young goslings. This is followed by a description of the close relationship between Ruth O’Leary—a woman who has raised many Canada geese—and her gosling ward, Little Sir. Heinrich uses these stories to make the point that we identify with geese because their bonding behavior (between mates as well as between offspring and parents) resembles our own. Throughout the book he finds occasion to note differences and commonalities between humans and birds.

The text moves sequentially through each step of the nesting process, from mate selection through the fledging of nestlings. In the course of a lengthy discussion of the diversity of mating systems in birds (monogamy, polygyny and polyandry are all found, and which form prevails is believed often to be related to food amount and distribution), Heinrich ruminates on the definition of love (“a temporary chemical imbalance . . . of the brain induced by sensory stimuli that causes us to maintain focus on something that carries an adaptive agenda”). He also explores the chemistry of emotional attachment, the role of hormones (oxytocin and vasopressin in humans, mesotocin and vasotocin in birds) in social bonding through pleasure, and the fitness benefits associated with forming pair bonds. In a chapter on penguins, he says that he has no problem with calling their feats of devotion displays of love, but he is quick to emphasize the importance of not ascribing moral values to the bonding behavior of birds.

After discussing how birds know when to nest, Heinrich covers sexual selection, competition among males for mating partners, and courtship displays. He recounts the findings of studies of singing behavior in male song sparrows, explaining that the number of songs in a male’s repertoire seems to be an honest signal of fitness: Individuals that sing a greater variety of songs produce clutches with more offspring. A large repertoire advertises vigor, for it requires a larger brain volume, which can only be achieved with better nutrition. This in turn suggests that the birds with larger song repertoires have been better or more successful foragers on average. Other topics touched on include migration, nest site and safety, nest materials and construction, egg production, egg recognition, and parenting in pairs.

The book is illustrated with Heinrich’s own drawings and photographs, with which he further demonstrates his prowess as a natural historian. The pictures alone make the book well worth the purchase price.