Bird Senses. Graham R. Martin

well as the more specialist reader. I have brought together a wealth of diverse information, but the book is not laden with references. Some of the more difficult topics are explained in boxes that can be referred to separately from the rest of the text. However, the reader can be assured that all statements are well supported by published material. There are suggestions for further reading which can be followed up should the reader be intrigued to dive deeper into the sensory worlds of birds.

      Graham Martin

      Emeritus Professor of Avian Sensory Science

      University of Birmingham, UK

      October 2019

A note on bird taxonomy and bird names

      The taxonomy and naming of birds is a matter of much debate. There are rival taxonomies and there can be heated debates. Furthermore, taxonomic revisions are frequent, especially now that classification based on genetic data is firmly established. The taxonomy, scientific and English names used in this book follow those of the International Ornithology Congress World Bird List (www.worldbirdnames.org). This is a freely open resource, with a lot of useful information, lists and spreadsheets, that can be downloaded. It is frequently updated. Names used in this book are based on version 9.2 (doi: 10.14344/IOC.ML.9.2) – but by the time you read this book it is likely that a newer version will be available from the IOC.

Acknowledgements

      I have studied the sensory world of birds for a lifetime and have worked alongside a wonderful range of keen and enthusiastic people. They have helped me to investigate a fantastic range of birds and their senses, and in many different locations. I thank them all for their support, and the exchange of ideas and enthusiasm. The names of them will have appeared as joint authors of papers or in the acknowledgement footnotes of papers. They have all contributed to this book in different ways, and I acknowledge their help and encouragement. Various colleagues have read parts of this book, but one person who has read it all and sorted out over-complicated language and many grammatical errors is Judith Burl, and I especially thank her for helping to bring the book to completion. I must also acknowledge the very skilful and helpful copy-editing of Hugh Brazier. With an eagle’s eye he caught my errors and checked many details. He gave the manuscript a deep clean and final polish. Finally, I thank people who over the years have attended talks that I have given to both specialist and lay audiences. They have asked intriguing questions and challenged me to explain more. In so doing they convinced me that there could be a readership for a book on this topic.

Chapter 1

       Senses and sensory ecology

      A Peregrine leaves its lookout in pursuit of a dove that it detected from more than a kilometre away. In under two minutes the dove is held firmly in the falcon’s talons. An Oilbird flies to its nest ledge inside a cave that is so deep that no light enters, darkness is total. In moonlight a Red Knot probes its bill through the squelchy surface of estuary mud, and without even lifting its bill detects and ingests a buried worm. A Great Tit searches through a wood and locates an infestation of caterpillars on a particular tree. The presence of the caterpillars is detected well before the Great Tit sees them.

      All of these are brilliant examples of bird senses in action. Each describes an instance of a bird using particular information to control one of its key behaviours. Included in these examples are the detection of prey at a great distance, precise seizure of a target by the feet or bill, location of a foraging site, mobility in the dark. Each bird’s survival requires that these actions are executed many times during its lifetime, and each action must be executed with high accuracy, both in time and in space.

      These examples were chosen because each depends on information gathered primarily by a different sense. Vision in the case of the Peregrine, hearing in the Oilbird, touch and taste in the Knot, and olfaction (the sense of smell) in the Great Tit. While information from one sense underpins each of these particular behaviours, these birds must also rely on information from a suite of different senses in order to conduct themselves safely during their everyday lives (Figure 1.1).

      FIGURE 1.1 Clockwise from top left: a Peregrine Falco peregrinus, an Oilbird Steatornis caripensis, a Red Knot Calidris canutus, and a Great Tit Parus major. Each species exploits information from a different sense to guide some its key behaviours. (Photograph of Great Tit by Francis C. Franklin [CC-BY-SA-3.0].)

      In all instances this different information is integrated and interpreted by the birds’ brains in a seamless fashion. We may focus our attention on the pursuit flight of the Peregrine, and wonder how it achieves such an impressive performance, but in reality the bird is moving rapidly from the execution of one task to another. No sooner has the prey been spotted than it is time to line up for its seizure, and the prey is grabbed with impeccable timing. We can even think of these birds as simultaneous multitaskers, for example looking out for predators or a competitor while searching for food, and each different task requires different information.

      Equally important is the range of environmental conditions in which these four birds carry out their key tasks – from total darkness to bright sunlight, from open habitats to the structural complexity of a forest. We could also choose examples of birds foraging in the open airspace, or finding food hidden on hard and soft surfaces, or beneath surfaces, or through the surface of water, or underwater at both shallow and deep depths, so deep that daylight hardly penetrates. Each habitat type presents different sensory and informational challenges which the birds must meet in order to live out their daily lives.

      Every bird species is special. By definition every species is unique, and much of what attracts our attention to particular birds is the fact that they are able to execute tasks that others cannot. It is this diversity of behaviour, as much as diversity of appearance, that makes watching and studying birds so rewarding.

      At one site, on one day, even at the same moment, we can see birds of different species acting in very different ways. Each is a specialist, and it is the parade of these specialisms that is behind much of the allure of watching birds. But while we can readily understand how obvious structural adaptations, particularly of their wings, bills, and feet, can allow different species to execute particular actions, it is easy to overlook the fact that those wings, bills, and feet must be guided accurately.

      There is no value in having a tool if it cannot be adequately controlled. A hammer that cannot be brought down accurately to hit a nail is useless. The hammer needs precision guidance in both time and space. In the same way, a long bill for grabbing a fish, or a short bill for seizing a seed, or a foot for grabbing another bird out of the air, are useless if they cannot be controlled and brought exactly to the target with precise timing. Each bill, foot, and wing requires specialised information to guide it to the right place and to get there at the right time. Actions need information, and different actions need different information.

      Unlocking the information

      The information that each bird species uses to guide its behaviours is a kind of secret. It is information that only the bird itself has direct access to. But for us to understand birds properly those secrets need to be unlocked in some way. The information that birds employ is not readily available to us as we look on. We need some tricks to help us get more than a hint of the information that a bird might be acting upon at any moment.

      As humans, we are trapped in our own world, with its own secrets. Our eyes do not allow us to see what the Peregrine sees as it bears down upon a pigeon. We cannot feel what