# As the pigeon flies

## Spatial Representation in Animals

Edited by:
Oxford University Press: 1998. 187pp. £45, $86, (hbk); £22.50,$40 (pbk)
Canada geese migrating at night. Credit: S. NIELSEN/ BRUCE COLEMAN LTD

As someone who struggles on a daily basis to remember where I left my car this morning, or even which direction on the freeway I should take, I marvel at the spatial memory and navigational capabilities of animals. What cues does a Siberian willow tit use to remember where it left its hidden food caches, given that it stored about half a million pine seeds in different sites throughout its territory several months earlier? How do monarch butterflies find the scarce, high mountain patches of the oyamel fir forest in central Mexico each autumn, more than 2,500 km away from the breeding grounds they just left? While the memory feats of a food-storing bird and the migratory capabilities of a butterfly may indeed be specialized examples, knowing how to get home is a problem most animals need to solve.

Spatial Representation in Animals brings together work on navigation and orientation in several different species, from honey bees to hamsters. It originated in a series of papers given at the 1995 winter meeting of the Association for the Study of Animal Behaviour, but, unlike many conference proceedings, the eight chapters in this book are easily accessible to advanced undergraduate and graduate students as well as to experts in the field. Another appealing feature is that the authors come from a variety of disciplines — from animal behaviour and behavioural ecology to neurophysiology and cognitive psychology — and this creates an integrative feel.

The book begins with a discussion of how animals use landmarks:Ken Cheng and Marciel Spetch's chapter focuses on mechanisms of landmark-based spatial memory in pigeons and gerbils, while Jochen Zeil and Tom Collett's chapter provides a different perspective, focusing on how arthropods rely on landmarks to find their way around. The theme of landmark use is taken up again in a chapter by Etienne Save et al., who discuss the concept of a ‘cognitive map’. They emphasize the fact that rodents may rely on several different categories of cues when navigating, and that the relative importance of these cues may depend on how the experiment is set up. There is much debate about whether rats, and other animals for that matter, possess a ‘cognitive map’ and how useful the concept is anyway. Given such controversy, I was somewhat surprised to discover that the seminal paper by Andrew Bennett (J. Exp. Biol. 199, 219-224; 1996) did not appear anywhere in the reference list, especially given his active participation in the conference.

Ariane Etienne et al. assess the importance of ‘dead reckoning’, or path integration, a mechanism of calculating distance and direction when travelling. Path integration allows the animal to make a straight-line return to its starting point without having to remember the landmarks that it has seen previously. As Etienne and co-authors point out, many animals, including humans, use path integration.

Another controversy involving the navigational mechanisms that animals use centres around the role of olfaction in pigeon homing behaviour, and it seemed particularly appropriate to find a chapter on this topic, by Verner Bingham, at a time when a consensus has finally been reached. The homing pigeon work is a wonderful example of the benefits of adopting an integrative approach to understanding the mechanisms of navigation at multiple levels. Salmon is another well-known model of homing, and the chapter by Victoria Braithwaite suggests that future work on the navigational and spatial memory capabilities of fish may be invaluable in extending our knowledge of animal spatial representations. This contrasts with the chapter by Peter Berthold, where the challenge is to summarize the vast body of literature on long-distance migration in birds.

A thorny area dear to my own heart concerns the role of the hippocampus in spatial representation, an issue that is addressed in the final chapter by David Sherry and Sue Healy. Evidence from both experimental and comparative studies suggests that the hippocampus is involved in spatial learning, but whether or not this is a primary function of the hippocampus remains an open question. An increasingly common view is that the hippocampus is more generally involved in learning and remembering events that depend on complex, configural cues, with spatial tasks merely being good markers with which to detect hippocampal function.

Spatial Representation in Animals provides an illuminating and up-to-date introduction to our understanding of the ways in which animals find their way about. It is definitely worth a read.

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