The Nesting Season: Cuckoos, Cuckolds, and the Invention of Monogamy

Bernd Heinrich is a highly regarded academic biologist - now emeritus - with the talent to do great science and write beautifully for the non-specialist. His books, mainly on birds and bees, are among the best examples of popular-science writing.

Prior to his first book, Bumblebee Economics (1979), few biologists had written about all that stuff that never appears in scientific journals: the blood, sweat and tears that collecting data in the field often entails. Reading the sanitised, staccato accounts in journals such as Science or Nature provides no sense of what fieldwork involves.

I was inspired by Heinrich's 1989 book Ravens in Winter, the story of what it is like to be a field researcher in extremely tough conditions (but then, Heinrich is a record-breaking marathon runner). Ravens describes both the academic and non-academic aspects of a specific study, making the science palatable and exciting.

The Nesting Season is a different kind of book in that it does not describe a specific study. Rather, it is a ramble through the home life of birds during the breeding season: a mixture of Heinrich's thoughts and experiences and the scientific literature.

Most birds breed monogamously. That is, a male and a female pair up, either for one nesting attempt or for as long as they both shall live, to rear offspring together. For more than a century, birds were assumed to be models of monogamy, although it was well known that a few species, such as pheasants and birds of paradise, were polygamous. The discovery in the 1980s that extra-pair matings and fertilisations were common in monogamous birds changed our entire view of avian mating systems. Birds may breed together as pairs, but they are not always faithful.

This revolution came about partly through recognising that natural selection operates on individuals (rather than groups), and partly through the fortuitous discovery of DNA fingerprinting, allowing researchers to unambiguously assign parentage.

Another discovery was that females sometimes dump extra eggs in the nests of members of their own species. This behaviour, with the unwieldy title of intraspecific brood parasitism, is pretty much what cuckoos and other brood parasites do to other species (technically referred to as interspecific brood parasitism).

Heinrich takes us on a somewhat erratic tour of the literature on these topics, interspersed with his own musings. The stories he tells are charming and intriguing, and his intimate connection with the birds in the woods and bogs surrounding his home brings it all to life. The text is further enlivened by a large number of superb colour photographs, mainly of nests, eggs and chicks, and by some of Heinrich's own watercolours.

He makes clear the evolutionary significance of the various breeding strategies he describes, especially in the case of males seeking extra-pair copulations and in the examples of both interspecific and intraspecific brood parasites. Basically, if you can dupe another individual to pay the energetic cost of rearing your offspring, and if there are no costs to yourself, then in selfish-gene terms, it pays to behave in this manner.

What remains a mystery is what females get out of being unfaithful. It seems logical that they benefit in some way simply because they often initiate such liaisons. Heinrich tells us that they are seeking better (or possibly different) genes for their offspring, but in truth, the scientific evidence for that is far from convincing.

There is still much to learn about the nesting seasons of birds, and this book should encourage others to continue the long and fruitful tradition of field biology.