Free Bird Sense by Tim Birkhead Page B

species. We cannot see ultraviolet (UV) light, we cannot echolocate, nor can we sense the earth’s magnetic field, as birds can, so imagining what it is like to possess those senses has been a challenge.
    Because birds are so staggeringly diverse, the question ‘What is it like to be a bird?’ is rather simplistic and it would be much better to ask:
     
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What is it like being a swift, ‘materialising at the tip of a long scream’? 3
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What is it like for an emperor penguin diving in the inky blackness of the Antarctic seas at depths of up to 400 m?
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What is it like to be a flamingo sensing invisible rain falling hundreds of kilometres away that will provide the ephemeral wetlands essential for breeding?
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What is it like to be a male red-capped manakin in a Central American rainforest, displaying like a demented clockwork toy in front of an apparently uninterested female?
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What does it feel like copulating for a mere tenth of a second, but over one hundred times a day, like a pair of dunnocks? Does it wear them out or does it bring immense pleasure?
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What is it like being the lookout for a group of white-winged choughs, watching in the short term for predatory eagles; in the longer term for an opportunity to assume the breeder’s mantle?
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What is it like, to feel a sudden urge to eat incessantly, and over a week or so become hugely obese, then fly relentlessly – pulled by some invisible force – in one direction for thousands of miles, as many tiny songbirds do twice each year?
     
    These are the types of question I’m going to answer, and I’ll do so by using the most recent research findings, but also by exploring how we arrived at our present understanding. We’ve known for centuries that we possess five senses: sight, touch, hearing, taste and smell; but in reality there are several others including heat, cold, gravity, pain and acceleration. What’s more, each of the five senses is actually a mixture of different sub-senses. Vision, for example, includes an appreciation of brightness, colour, texture and motion.
    Our predecessors’ starting point for understanding the senses was the sense organs themselves – the structures responsible for collecting sensory information. The eyes and ears were obvious, but others, such as that responsible for the magnetic sense of birds, are still something of a mystery.
    Early biologists recognised that the relative size of a particular sense organ was a good guide to its sensitivity and importance. Once the anatomists of the seventeenth century discovered the connections between sense organs and the brain, and later realised that sensory information was processed in different regions of the brain, it became apparent that the size of different brain regions might also reflect sensory ability. Scanning technology, together with good old-fashioned anatomy, now allows us to create 3 -D images and measure with great accuracy the size of different regions of both human and bird brains. This has revealed, as Richard Owen predicted, that the visual regions (or centres, as they are known) in the kiwi’s brain are almost non-existent, yet its olfactory centres are even larger than he thought. 4
    Once electricity had been discovered in the eighteenth century, physiologists like Luigi Galvani quickly realised that they could measure the amount of ‘animal electricity’ or nervous activity in the connections between sense organs and the brain. As the field of electrophysiology developed it became clear that this provided yet another key to understanding the sensory abilities of animals. Most recently, neurobiologists have used different types of scanners to measure activity in different regions of the brain itself to inform them of sensory abilities.
    The sensory system controls behaviour: it encourages us to eat, to fight, to have sex, to care for our offspring, and so on. Without it we couldn’t function. Without any one of our senses life would be so