Bipedal mammals can’t really ‘know’ what it is like to be a penguin, a flamingo or a tropical hummingbird, but we can indeed marvel at the difference
Who’d be a bird anyway? Chickens have bi-focal vision: one eye for the close-up work of pecking seed; one for the fox on the horizon or the hawk in the sky. Peregrine falcons don’t swoop directly on prey – as the crow flies, to coin a phrase – but in a wide arc, using the right eye. Mallard ducks on the ground and swifts on the wing both nod off with half the brain at work and one eye wide open watching for danger.
Nightingales in Berlin have to up their vocal performance by 14 decibels to be heard over the traffic; great tits in the city keep down the volume but change the pitch or the frequency to get the message across. The oilbird of Ecuador sleeps with its eyes closed but then it could even fly with its eyes closed: like a bat, it uses echolocation to work out where it is in total darkness.
The ears of the great grey owl are asymmetrical – higher on one side than the other – the better to pinpoint prey on the vertical as well as the horizontal axis. That is why it can swoop on a mouse under the snow. All listeners can localise a source of sound by unconsciously measuring the difference in time as the waves arrive at each separate ear: for small birds, this would dwindle to less than a millionth of a second so little birds move their heads from side to side to increase the range.
Avian hearing ability varies according to the season. So do other features. In winter, the testes of the cock sparrow dwindle to the size of a pinhead; with the nesting season, they swell to the volume of a baked bean. The ability to sing tends to surge with the urge to nest. A hormonal response that varies with daylight length also does strange things to the brain: the ability to acquire and deliver song dwindles, and the relevant area of the bird brain shrinks, in the winter. This is, says Tim Birkhead in Bird Sense, “a sensible energy-saving tactic” because brains are a big expense: the human brain for instance uses 10 times as much energy as any other organ.
Books like this often deliver far more value than their titles might suggest. Bipedal mammals with limited vision and hearing that fades with age and too much rock music can’t really “know” what it is like to be a penguin, a flamingo, or a tropical hummingbird, but they can marvel at the difference. So the continuous reference to a human template also provides a lot of useful general instruction in physiology, anatomy and evolution. The simple attempts to address each question of bird sense – taste, smell and touch as well as hearing and vision – involves science history, and not just, for instance, the first scholarly papers on echo location in barn owls…
The chapter on avian emotions – including the search for evidence of romantic love in apparently monogamous species – is navigated (yes, there’s a chapter on navigation too) with caution and Birkhead delicately adds “I am not going to speculate about the emotions that might be involved in avian infidelity”. This book kicked off as three-to-one favourite to win the Royal Society Winton Prize. I can see why.
• The winner of the 2013 Royal Society Winton Prize for Science Bookswill be announced on Monday 25 November
• Tim Radford’s geographical reflection, The Address Book: Our Place in the Scheme of Things, is published by Fourth Estate