Читать книгу Bird Senses - Graham R. Martin - Страница 21

How can sensory performance be quantified? In essence we want to ask some specific questions. We want to ask a Barn Owl and a Starling what it can see and hear, a Sanderling what it can feel at its bill tip and taste on its tongue, a Storm Petrel what it can smell (Figure 2.4).

FIGURE 2.4 Four bird species which differ markedly in their senses and how they use them to gain information that is used to guide their behaviour, especially their foraging. Clockwise from top left: Common Starling Sturnus vulgaris, Barn owl Tyto alba, Leach’s Storm Petrel Oceanodroma leucorhoa, Sanderling Calidris alba. These birds differ in their vision, hearing, sense of smell, and sense of touch. Furthermore, each species relies upon a different primary sense to guide its behaviour. They also differ in how they combine and complement information gained through different senses. In short, each bird lives in a different sensory world. (Photo of Starling by Pam P. Parsons [West Bay Dorset, via Flickr as Pam P Photos], Barn Owl by Graham White [CC BY-NC-SA 2.0], Storm Petrel by C. Schlawe [public domain], Sanderling by J. J. Harrison [https://www.jjharrison.com.au, CC BY-SA 3.0].)

Sensory science is mainly concerned with these kinds of questions, with revealing sensory capacities and discovering the mechanisms that underpin them. Sensory ecology, however, takes this information further and is more interested in revealing what sensory capacities are in play in a particular situation, or in finding out how an animal uses the information that it has available to guide its key behaviours.

The aim of sensory scientists has been to manipulate just one or two parameters of a stimulus at a time, and if possible to use those manipulations to determine the limits of sensory performance. If this can be done in a comparable way across a range of species then we should be able to say with some confidence that this species is more sensitive than that one, or this species is able to gain information over a wider range of parameters. These are often the kinds of things that birdwatchers, journalists, and TV documentary makers are keen to know about.

I am often asked whether this or that species is ‘better’ or ‘worse’ than humans. But the biologically relevant question is whether the species is better or worse than the species that it is competing with. What is important to a sensory ecologist is using this information to understand what information an animal has available to guide its behaviour in real-world tasks, and understanding how information from different senses might be integrated.

It does not matter whether an animal’s senses are ‘better’ or ‘worse’ than humans. Humans are, after all, just one species, adapted to living in certain types of environments through the conduct of particular behaviours, so comparison with humans may not be important. The desire to compare another species’ sensory performance with humans is born of an anthropocentric view of the world. It is a viewpoint which provides a strong pull. I try to resist it, but we shall not be able to escape from it completely in this book.

Measuring senses in a similar way in different species does have great value for comparative studies and also for helping to understand the basic mechanisms that underlie a sense. For example, if differences are found between species in their ability to see detail, and systematic differences are also found in the structure of the eyes’ optics or retinas, then it is possible to start piecing together an understanding of basic mechanisms. This in turn allows the possibility of being able to predict what another species might be able to see just from knowledge of its eye structure.