Читать книгу Bird Senses - Graham R. Martin - Страница 12

Sensory ecology is the branch of science that enables us to understand how information controls animals’ interactions with their environments. In essence sensory ecology allows us to enter and understand the worlds of other species. When we apply the ideas of sensory ecology to birds, we move close to appreciating the world ‘through birds’ eyes’. We also come to understand the proper meaning of a ‘bird’s-eye view’.

A bird’s-eye view is a much-used metaphor. It pops up everywhere, from highbrow literature, to journalism, to advertising. It is shorthand for appreciating the world from a fresh perspective, but often it is used to imply that we can actually see the world through the eyes of a bird. Sensory ecology casts doubt on that very notion. By going beyond just vision and eyes, a metaphorical bird’s-eye view throws light upon all senses and on how information from them is integrated in the conduct of particular tasks. In so doing it helps us delve deep into the problem of understanding ‘reality’ from a human perspective (Figure 1.2).

FIGURE 1.2 A Golden Eagle Aquila chrysaetos stares into a camera lens. A White-tailed Eagle Haliaeetus albicilla flies over Paris carrying a camera as part of an advertising stunt to market a new camera. The advertisement carried the strapline, ‘The 100% eagle-eye view’. These are two species credited with the most acute vision in all animals, but what do they actually see? What is an eagle’s-eye view? Can it be captured in a single photographic image? (White-tailed Eagle from Sony Creative Commons; Golden Eagle by the author.)

Sensory ecology tells us about the ways in which different animals gather information from their environments, about the factors that ultimately limit what can be detected, and the ways in which information from different senses is brought together to underpin life in different habitats. Sensory ecology reveals to us that there are very many ‘birds’-eye views’, many different sensory worlds, and that none is the same as ours. Our own sensory ecology is as specialised as those of Peregrines, Oilbirds, Knots, or Great Tits. We may wish to understand the world through their senses, but we can only ever experience one view of the world, our own. The best we can do as regards the worlds of other species is to know about them, we cannot ever experience and properly know their worlds.

Sensory ecology can provide data on the sensory performance of other species. It can place these data in a comparative framework and tell us how species differ one from another. It is often tempting to use the terms ‘better’ or ‘worse’ when comparing the sensory capacities of species but, on the whole, these terms are not useful. This is because the senses of each species are adapted for the conduct of different tasks in different environments. There may be optimal solutions to different sensory challenges, but they are no better or worse than each other. They are fit for the purposes that they evolved to meet.

Sensory ecology helps to determine why and how performance is limited by different environments and by the physiology of a species. Sensory ecology also indicates how information from one sense might be traded off against that provided by other senses for the optimal conduct of particular actions.

Modern technology can help in the tasks of characterising the sensory performance of different species, but it must not be thought capable of providing simple answers. Experiencing the world as a Peregrine sees it cannot be achieved by strapping a video camera to its back. Such footage makes thrilling viewing and gives insights into the life of a Peregrine, but it cannot give us the real Peregrine’s-eye view. The photograph or film, viewed on a flat screen, still gives us only a view of the world that is two-dimensional and ultimately filtered by human eyes and brains. Understanding a bird’s-eye view has to be achieved by piecing together many different sources of information about vision, not to mention about how visual information interacts with information from other senses.

Sensory ecology also shows us that we need to see the behaviours of birds in their proper context, the context of the actual challenges that birds face in their natural environments. For example, what is natural night-time really like? How does it change with habitat or with the annual cycle? We can also ask under what natural light conditions a Peregrine can best detect distant prey, and how changing light levels affect its abilities. Does our knowledge of these explain when and how it hunts? Similarly, we might ask questions about how soft and wet mud has to be for a Knot to be able to detect and identify a food item that is near the tip of its probing bill. We might also ask why some birds are particularly prone to flying into power lines. Is it due to limitations of their senses?

To answer all of these questions, and very many more, requires the senses of birds to be seen in both an ecological and an evolutionary context. In other words, knowledge of senses gained through careful laboratory-based studies and field observations needs to be placed in the context of the wider world in which animals evolved and exist today.