Birds are dinosaurs. Some people find them frightening. Those creepy reptilian feet! Those expressionless faces! Many others find them charming and beautiful, and become intensely curious about what is going on inside their little heads. What are they perceiving? Feeling? Because their evolutionary ancestry diverged from ours so long ago, we can't assume they are like us. Yet many birds behave in ways that seem familiar. We share their daytime habits and tendencies to socialise by vocalising, forming pair relationships and raising babies together. We seem more like birds than mice, the darlings of biomedical research.
Yet we do not know, and may never know, whether birds are conscious in the sense that we are. Nonetheless, access to their inner worlds can begin by asking what they detect from their environment, just as the science of human psychology began with the study of sensation and perception. What senses do birds have? (We have more than the traditional five, and so do they.) How do they work? How are they used to navigate thousands of miles through featureless terrain, and to form and maintain the lifelong pair bonds of swans and zebra finches? What does the world look like when each eye has two foveas (zones of the retina of greatest acuity used for "looking at" something) instead of one, as in our eyes?
Research on the sensory systems of birds has produced dozens of amazing discoveries that are clearly and entertainingly presented in this delightful book, which should interest a wide audience and not just bird lovers. Some birds can see ultraviolet wavelengths of light and use them to judge the attractiveness of potential mating partners. Owls with markedly offset ears use hearing to catch mice in complete darkness. Birds can detect the Earth's magnetic field and use it to navigate. The hunt is on to find their magnetic field detectors.
The chapter on touch provides Tim Birkhead with a golden opportunity to launch into one of his favourite scientific topics: bizarre copulatory organs. Only a small percentage of bird species, such as buffalo weavers, have such unusual equipment. Do the males derive pleasure from using it? Birkhead provides a tentative "yes" via a hilarious report of a student who massaged a male buffalo weaver to orgasm.
The author has devoted much of his scientific career to his passion for birds. More unusually, he is also a superb popular science writer. Here he again displays his intense intellectual curiosity and enthusiasm for natural history without compromising the quality of the science or the scholarship. The result is an engaging mixture of personal anecdotes from all over the world, lesser-known histories of science and expert renditions of current knowledge. Narrative flow comes from the scientific process itself, with plenty of stories about the detective work and hypothesis-testing experiments required to answer questions. How was it shown that oilbirds used their ears and the echoes of their calls to fly at night? By plugging their ears with cotton, as Don Griffin did. With its wit and charm ("first, catch a duck" if you want to see the touch receptors at the bill tip yourself), this book provides an excellent education in how the science of animal biology is practised and why the path forward is meandering instead of straight, as when successive generations of scientists disagreed about whether vultures used olfaction to locate dead animals. (They do, but prefer freshly dead to rotten targets.)
What else do we need to know to get inside a bird's head? Perception, cognition and emotion are products of the nervous system and especially the brain. Quite understandably, given the book's focus on the senses, the approach to those higher processes is "bottom up", a widely held view stemming from the days when all behaviour was viewed as reflex. But perception and cognition are also "top-down" processes in humans, and very likely other animals as well, with brains constantly generating educated guesses about what might be out there in the world to compare with the data coming in. Relative to body size, bird brains are as large as mammal brains. Now we need to know much more about what those brains do with all that is captured by those amazing sensory systems. The next decade will bring important discoveries and, one hopes, a similarly accessible and successful account of avian brain science.
Bird Sense: What It's Like to Be a Bird
By Tim Birkhead
Bloomsbury, 288pp, £16.99
Published 2 February 2012