Thought-provoking argument suggests feathered friends are no birdbrains

Bird Sense, What it’s like to be a bird

Tim Birkhead

Bloomsbury, £16,99, £9.98.

Review Richard Collins

Thomas Nagle’s essay What is it like to be a bat appeared in the Philosophical Review in 1974. Nagle raised an intriguing question; how do creatures other than humans perceive the world? His theme was animal subjectivity in general, the cognitive world of bats offering a colourful example of the difficulties presented in “reductionist” approaches to it.

Bats “picture” the world by transmitting sound pulses and interpreting the echoes reflected from surrounding objects. We can, with difficulty, imagine how the world might appear if we had to do the same but, in Nagle’s view, this would give little insight into the mindset, assuming there even is one, of a bat.

In a nod towards the famous essay, Tim Birkhead’s Bird Sense is subtitled what it’s like to be a bird. Here, animal subjectivity is examined in relation to birds, which resemble us more closely than some creatures to which we are more closely related. Warm-blooded, birds see in colour, communicate visually and vocally, form long-term pair bonds and care for their young.

Birkheads’s perspective differs from that of Nagle who is a philosopher, not a scientist. He quotes Irish philosopher William Molyneux’s dictum that “the eye is only the organ or instrument, ’tis the soul that sees by means of the eye”, but top-down philosophical speculation doesn’t carry much weight with him.

For a scientist to take an assertion seriously, it must be grounded in empirical observation and measurement. Accordingly, he approaches the body-mind problem from the bottom-up as it were, by examining the workings of the sense organs, one by one. Not surprisingly, the author of The Wisdom of Birds, an Illustrated History of Ornithology peppers his text with colourful observations on the origins of the various ideas he discusses.

We speak of our “five senses” although, in fact, we have several more. Birds, we tend to think, are similarly endowed but actually they have additional ones, the most mysterious being a sensitivity to the Earth’s magnetic field.

“A bird,” it has been said, “is a wing guided by an eye” and, indeed, some birds have extraordinary powers of sight. Most, perhaps all, are sensitive to ultra-violet light. We humans can’t envisage a colour spectrum which includes the ultra-violet, nor is this the only difference between their visual world and ours. The image on the retina of the human left eye differs somewhat from that of the right but our nervous system combines the two images into one. Many bird species, however, have eyes at the sides of the head. They receive images so different from each other that they can’t be combined. Do birds see two images at once? It turns out that birds use their left and right eyes for different tasks, sidedness in brain functioning allowing them to operate simultaneously. Sleeping birds, for example, can still observe their surroundings by opening one eye, as Chaucer noted in the Canterbury Tales of 1386

“... smale fowles ... slepen at the night with open ye.”

The blackbird, hunting for worms on the lawn, will pause and turn its head from time to time. Is it looking for signs of a worm, such as movements in the roots of grass, or is it listening? Ornithologist Frank Heppner played white noise to captive American robins as they searched a lawn for worms. The sound made no difference to their foraging success, so he concluded that the birds were seeing, rather than hearing, their prey. Other ornithologists challenged this conclusion. They removed all worm casts, covered worm holes in the ground and showed that the robins could still detect their prey. They concluded that both senses, and possibly also touch, were being used.

The sense of touch has received little attention from ornithologists but laying fragile eggs and not breaking them when incubating, requires tactile sensitivity of a high order. Assessing the temperature of eggs, so critical to their successful hatching, depends entirely on touch. Even birds which rely on compost mounds to heat and incubate their eggs constantly monitor the temperature of their pile by inserting the bill into it and adding or removing material.

Birkhead, whose doctoral thesis was on guillemots, recalls how an individual on its breeding ledge at Skomer Island could recognise the call of its mate several hundred metres out to sea. Taste and smell are related faculties. Received wisdom has it that, apart from the tube-nosed seabirds and some carrion feeders, birds have little sense of either. So much of their skull cavities, it’s usually claimed, are taken up by the huge eyeballs, that brain space is limited and there is little room for the olfactory lobes. Sensitivity to odours, the theory goes, is a luxury which few birds can afford. Birkhead, however, cites recent studies which show that taste and smell play a far more significant role in the lives of birds than was once believed and this is true, even of species which might appear to have little need of these senses.

The integration of the various senses raises issues of ‘mind’. Are birds self-aware? Do they experience emotions? Jeremy Bentham (1748 — 1832) pointed out the key question is not whether animals can reason but whether they suffer. This was for long a no-go area for biologists. Then, in 1976, Don Griffin published The Question of Animal Awareness. Initially, the book was greeted with derision but, gradually, interest in the possibility of animal awareness grew. The nature of consciousness, human or animal, is a major topic in science today. Birkhead, too, seems fearful of entering this minefield but, with his back to the wall, he concedes birds experience sensations of stress and pain. A phrase of Ludwig Wittgenstein’s comes to mind:

‘whereof one cannot speak, thereof one must be silent’.

This is an entertaining informative and thought-provoking book which should appeal to anybody with an interest in birds or any animal group.

* Outdoors: Monday