Bird Sense (3 page)

Ideas are important in another way because, if an idea results in a discovery, then this can make a scientist’s reputation. Science is about being first, and about being the person(s) associated with a particular discovery, exemplified by James Watson’s and Francis Crick’s discovery of the structure of DNA in
1953
.

Where, you might ask, do scientists get their ideas from? Partly from the body of knowledge they already have, partly from discussing their work with other scientists, but sometimes from casual observations or comments made by non-scientists. As we’ll see, casual comments have played a vital role in alerting scientists to particular bird senses. One of the most intriguing, described later, is the sixteenth-century Portuguese missionary in Africa who recounted how, whenever he lit beeswax candles, little birds came into the sacristy to eat the melted wax.

Once a scientist has had an idea and tested it in the most rigorous way she or he can devise, usually through some kind of experiment, they might then present their results by giving a talk at a scientific conference. This allows them to gauge how others view their results. On the basis of this the scientist may or may not modify their interpretation. The next stage is to write up the results so that they can be published as a paper in a scientific journal. The editor of the journal receives the scientist’s report and sends it off to two or three other scientists (referees) who decide whether or not it merits publication. Their comments in turn may provide the author with new ideas and an opportunity to re-analyse some of their results and modify the report. If, on the basis of the referees’ comments, the manuscript is deemed acceptable it is then published either as a hard copy and/or an on-line version in the scientific journal. Even then, the process isn’t over, for once the report is published it becomes available to all other scientists, who can either criticise it or take inspiration from it for their own studies.

In a nutshell, then, this is the tried and tested process of science and it hasn’t changed much since the late
1600
s, when the first scientific journal was published. Throughout this book we’ll meet the individuals who, through an unequal combination of perspiration and inspiration, are responsible for the scientific discoveries associated with bird senses. Typically, the accounts of their discoveries published in scientific journals are written concisely and with a fair amount of jargon – in both cases to save space. Jargon isn’t a problem for those in the same field, but to those outside a particular research area, and to the non-specialist, it can be a major obstacle to understanding. What I have done in this book is to take the scientific papers relating to the senses of birds, and convey their findings in everyday language. I have avoided jargon wherever possible, but where it is completely unavoidable I have tried to briefly explain the term, and for those requiring a bit more explanation I have provided a glossary at the back of the book. One of the benefits of writing what I hope is an accessible account of the senses of birds is that it made me ask my sensory colleagues some rather basic questions. In doing so I discovered that there were many aspects where I assumed the answers would be known, only to find that there is a great deal still to be discovered. This is inevitable since we cannot know everything, but, of course, it can be a little frustrating when we find that the answers to what seem like very simple question are not known. On the other hand, such gaps in our knowledge are exciting because they identify new opportunities for researchers interested in the senses of birds.

Bird Sense
is about how birds perceive the world. It is based on a lifetime of ornithological research and a conviction that we have consistently underestimated what goes on in a bird’s head. We already know quite a lot, and we are poised to make more discoveries. This is the story of how we got to where we are, and what the future holds.

My entire career has been spent studying birds. That doesn’t mean I do nothing else: being an academic in a university means I also spend a fair amount of time teaching undergraduates (which I enjoy), and rather less time on administration (which I don’t). I started watching birds at the age of five, encouraged by my father, and was lucky to be able to turn my passion for birds into a career as a scientist. It is a career that’s taken me all over the world, from the Arctic to the tropics, studying birds. As a result, and largely by working with my research students and colleagues, I have acquired privileged insight into the biology of a fair number of different bird species. Two, however, have preoccupied me: the zebra finch and the common guillemot. My experience of keeping zebra finches and other birds as a boy, combined with endless hours watching wild birds, honed my observational skills and gave me what I like to think of as a kind of biological intuition about the way birds operate. Hard to define, but I’m sure the many hours I spent watching birds helped to make me an effective researcher. Certainly, it set me up for the twenty-five years, so far, that I have spent studying zebra finches.

My other main study species is the common guillemot. This was the subject of my PhD and I spent four blissful summers on Skomer Island, off the western tip of South Wales, studying this species’ breeding behaviour and ecology. That was almost forty years ago, and I have been back to Skomer and its guillemots almost every summer since then. That’s a lot of guillemot hours in total, and as I was writing this I realised that I have probably devoted more time to watching and thinking about guillemots than to any other species. This is reflected in the book, for guillemots have given me tremendous insight into what it’s like to be a bird.

Probably not all scientific ornithologists feel that way about their study species, but I certainly do and I think – at the risk of seeming anthropomorphic – it is because guillemots are so similar to humans. They are extremely social, forming friendships with their neighbours and occasionally helping them with childcare; they are monogamous (albeit with the occasional fling); male and female pair members work together to rear offspring, and pairs sometimes remain together for as long as twenty years.

The other benefit of studying birds for so long is that one gets to know, either personally or by email, a large number of other ornithologists, and perhaps the most rewarding aspect of writing this book has been the enthusiasm with which my colleagues have shared their hard-won knowledge. Without exception, everyone I contacted to ask questions or to seek clarification responded helpfully. I am grateful to them all (and I apologise if I’ve overlooked anyone): Elizabeth Adkins-Regan, Kate Ashbrook, Clare Baker, Greg Ball, Jacques Balthazart, Herman Berkhoudt, Michel Cabanac, John Cockrem, Jeremy Corfield, Adam Crisford, Susie Cunningham, Innes Cuthill, Marian Dawkins, Bob Dooling, Jon Erichsen, John Ewen, Zdenek Halata, Peter Hudson, Alex Kacelnik, Alex Krikelis, Stefan Leitner, Jeff Lucas, Helen Macdonald, Mike Mendl, Reinhold Necker, Gaby Nevitt, Jemima Parry-Jones (of the International Bird of Prey Centre), Larry Parsons, Tom Pizzari, Andy Radford, Uli Reyer, Claire Spottiswoode, Martin Stevens, Rod Suthers, Eric Vallet, Bernice Wenzel and Martin Wild. I am especially grateful to Isabel Castro who, having promised me a kiwi experience of a lifetime, didn’t disappoint. Thanks to Geoff Hill for taking me kayaking in the swamps of Florida in search of the ivory-billed woodpecker; we didn’t see one but the experience was unforgettable. Special thanks to Patricia Brekke for persuading me to visit Tiritiri Matangi Island in New Zealand to see her stitchbirds; to Claire Spottiswoode for introducing me to the wonders of honeyguides and prinias in Zambia; to Ron Moorehouse who arranged for me to visit Codfish Island, New Zealand, to see kakapo up close – an extraordinary privilege for which I am very grateful. I thank Nicky Clayton for patiently answering my questions about cognition. Peter Gallivan and Jamie Thomson provided some much-appreciated help with the references. Graham Martin kindly read and commented on chapter
1
, and Herman Berkhoudt did the same for chapter
3
. I am particularly grateful to Bob Montgomerie for years of constructive criticism and friendship, and for reading and commenting on the entire manuscript. Similarly, I thank Jeremy Mynott for his perceptive comments on the manuscript. My agent Felicity Bryan provided her usual invaluable advice, and Bill Swainson and his team at Bloomsbury were exemplary in their support. As always, I thank my family for their indulgence.

1

Seeing

The wedge-tailed eagle has the largest eye relative to body size of any bird. Thumbnails (
from left to right
): the retina of an eagle showing the two fovea and the pecten (
dark
); a cross section through an eagle’s eye; cross section through an eagle’s skull showing the relative size and position of the eyes and the line of sight of the two fovea (
arrows
).

The falcon’s sensory world is as different from ours as is that of a bat or a bumble-bee. Their high-speed sensory and nervous systems give them extremely fast reactions. Their world moves about ten times faster than ours.

Helen Macdonald,
2006
,
Falcon
, Reaktion Books

As a child I once had a conversation with my mum about what our dog could or could not see. On the basis of something I had heard or read, I told her that dogs could see only in black and white. Mum was not impressed. ‘How could they possibly know that?’ she said: ‘We cannot look through a dog’s eyes, so how could anyone know?’

In fact there are several ways we can know what a dog, a bird or, indeed, any other organism can see, for example either by looking at the structure of the eye and comparing it with other species, or by behavioural tests. In the past, falconers unwittingly performed just such a test – not with falcons, but with shrikes.

This elegant little bird is used, not to attract the hawk as might be supposed, but to give notice of its approach. Its power of vision is perfectly marvellous, for it will detect and announce the presence of a hawk in the air long before the latter is discernible by human eye.
1

The ‘elegant little bird’ is the great grey shrike and the trapping method an elaborate one, involving a turf hut in which the falconer is concealed, a live decoy falcon, a wooden decoy falcon, a live pigeon and – crucially – a great grey shrike (known also as a butcher bird) tethered outside its own miniature turf hut.

James E. Harting, falconer and ornithologist, saw this method in action during October
1877
near Valkenswaard, in the Netherlands, a traditional location for trapping migrating falcons. Here’s how he described it:

We take our seats on the chairs in the hut, and fill our pipes . . . Suddenly our attention is attracted by one of the shrikes. He chatters and appears uneasy. He crouches and points . . . He jumps off the roof of his hut, and prepares to take shelter within it. The falconer says there is a hawk in the air.
2

They watch and wait, but it turns out to be a buzzard and the falconer isn’t interested. But later:

Look! The butcher-bird is pointing again. There is something in the air. He chatters and quits his perch . . . We look in the direction indicated, and strain our eyes, but see nothing. ‘You will see him presently’, says the falconer; ‘the butcher-bird can see much farther than we can.’ And so he can. Two or three minutes afterwards on the far distant horizon of that great plain [of Valkenswaard] a speck comes into view, no bigger than a skylark. It is a falcon.
3

As the raptor approaches, the nature of the shrike’s agitation informs the falconer of the species. Even more remarkably, the shrike’s behaviour also tells the falconer
how
the raptor is approaching: swiftly or slowly; high in the sky or low over the ground. The shrike – an invaluable asset – is kept safe from the raptor’s clutches by the provision of that little turf hut.

Other trapping methods employed shrikes as decoys, relying on the extraordinary visual acuity of the raptors to see them as potential prey. Expressions such as ‘eagle-eyed’ or ‘hawk-eyed’ attest to the fact that for a very long time we have known about the extraordinary vision of falcons and other birds of prey.
4

One reason falcons see so well is because they have
two
visual hot spots at the back of each eye – two foveas – rather than the one that humans have. The fovea is simply a tiny pit or depression on the retina at the back of the eye where blood vessels are absent (since they would interfere with the clarity of the image) and the density of photoreceptors – cells for detecting light – is greatest. As a result, the fovea is the point in our retina where the image is sharpest. The falcon’s two foveae contribute to its excellent vision.