John Mcewen

How do birds fly south?

How do birds fly south?
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Bird Sense

Tim Birkhead

Bloomsbury, pp. 265, £

Did you know the external ‘shell’ of the ear is the pinna? That a woman’s oestrogen level alters the way she hears the male voice, making it richer, and thus may affect her choice of mate? That Pride and Prejudice was published the year (1813) that Europeans discovered the kiwil? That Leonardo da Vinci ‘was one of the first to comment on the extra-ordinary tongue of the woodpecker’? These are some indicators of the general interest of this book, subtitled ‘What It’s Like to Be a Bird’, which demonstrates humans are much more birdlike than previously thought.

The principal reason is that, like them, we rely most on vision and hearing. Ever more sophisticated research reveals that birds also share our other sensory perceptions, touch, taste and smell. The author, a science professor at Sheffield University whose principal subject of research is bird promiscuity (what a dinner-party opener), even argues convincingly that birds have feelings. The subject is unavoidably scientific but written for a general readership without populist condescension.

There has been a sea change in our understanding of animal behaviour. The retired sensory biologists Tim Birkhead questioned complained that their research had been either unconsidered or their discoveries simply not accepted. Nonetheless, these remain early days. ‘We have a good basic understanding of at least some of the senses of birds, but the best is yet to come,’ is the challenging conclusion.

There are seven chapters — Seeing, Hearing, Touch, Taste, Smell, Magnetic Sense, Emotions — each with its quota of fascinating and often incredible revelations. The subject of emotions is probably the most contenti ous, verging as it does on the scientifically forbidden territory of anthropomorphism. The difference between our bodies and birds’ is invariably one of modification rather than kind. Birds, for example, have a nictating (nictare, to blink) membrane, a translucent additional eyelid. Our nictating membrane exists as a mere remnant, the tiny pink nub in the inner corner of the eye.

The flightless, near sightless kiwi can use its long nose of a beak to smell an earthworm through 15 cm of soil; but the avian ability which inspires the greatest awe is migration. Paradoxically it has been through the study of caged birds that most understanding of their navigational mechanisms has been gained. Even 18th-century observers noted that certain pet birds hopped agitatedly in their cages at the times they would normally have been migrating. Only now are we beginning to understand that birds are guided by a magnetic compass, which enables them to detect magnetic fields via chemical reactions inside individual cells throughout their body.

Birkhead’s research has centred on guillemots. The way technology has transformed this fieldwork is dramatically illustrated by the retrieval of a geolocator from the migratory guillemot’s leg. The most difficult and dangerous part of the operation is snatching the bird off the cliff-face by the rustic means of a pole and noose. The geolocator is plugged into a laptop and the data downloaded. ‘Lying on the grass, we cluster round the laptop, shading the screen from the sun. A map of the world appears, pinpointing every ten-minute fix, until the bird’s entire year of travel emerges.’

As one would expect it is a given that God has been replaced by Darwin. ‘The recognition that natural selection provided a much more convincing explanation than God or natural theology for the perfection of the natural world was one of  the fundamental shifts in our understanding of nature.’ Those who have faith in divinity will surely not find the professor’s assumption contradictory.

And what of science and technology? Birds, especially small birds, have declined over the last 50 years as fast as science has progressed. Why? Because of the needs of  a human population vastly increased by science and technology. Will we too end up as helpless as those dangling guillemots, our viable futures recorded and found wanting? We may be doomed to be all too like birds indeed.