On the Move: How and Why Animals Travel in Groups
Group movement is only rarely migration, though the two phenomena are overlapping subsets. An example of group movement that demands some explanation is that found in chimpanzees. One might ask why chimps are ever in groups, given that one of the most important things a chimp can do in a day is to feed, and for many reasons they do better at feeding when alone. But chimps are a social species, and as such, often coordinate their movements and their overall togetherness. Do they use vocalizations? Hand signals? Other body-related signals (as cows are supposed to do)? Or do they just all happen to get up and go to the same place at the same time? Well, it’s complicated, and chimpanzee and more generally primate movement and group cohesion is explored in detail in chapters by all the usual (suspect or not) primate and mammal researchers.
To give you an idea of the scope and intensity of this coverage, I’ve lifted the table of contents:
Part One – Ecological Costs and Benefits
1. The Physiology and Energetics of Movement: Effects on Individuals and Groups by Karen Steudel
2. Determinants of Group Size in Primates: The Importance of Travel Costs by Colin A. Chapman and Lauren J. Chapman
3. A Critical Evaluation of the Influence of Predators on Primates: Effects on Group Travel by Sue Boinski, Adrian Treves, and Colin A. Chapman
4. Mixed-Up Species Association and Group Movement by Marina Cords
5. Territorial Defense and the Ecology of Group Movements in Small-Bodied Neotropical Primates by Carlos A. Peres
Part Two – Cognitive Abilities, Possibilities, and Constraints
6. Group Movement and Individual Cognition: Lessons from Social Insects by Fred C. Dyer
7. Spatial Movement Strategies: Theory, Evidence, and Challenges by Charles Janson
8. Primate Brain Evolution: Cognitive Demands of Foraging or of Social Life? by Robert A. Barton
9. Animal Movement as a Group-Level Adaptation by David Sloan Wilson
Part Three – Travel Decisions
10. Evidence for the Use of Spatial, Temporal, and Social Information by Primate Foragers by Paul A. Garber
11. Homing and Detour Behavior in Golden Lion Tamarin Social Groups by Charles R. Menzel and Benjamin B. Beck
12. Comparative Movement Patterns of Two Semiterrestrial Cercopithecine Primates: The Tana River Crested Mangabey and the Sulawesi Crested Black Macaque by Margaret F. Kinnaird and Timothy G. O’Brien
13. Mountain Gorilla Habitat Use Strategies and Group Movements by David P. Watts
14. Quo Vadis? Tactics of Food Search and Group Movement in Primates and Other Animals by Katharine Milton
Part Four – Social Processes
15. Social Manipulation Within and Between Troops Mediates Primate Group Movement by Sue Boinski
16. Grouping and Movement Patterns in Malagasy Primates by Peter M. Kappeler
17. How Monkeys Find Their Way: Leadership, Coordination, and Cognitive Maps of African Baboons by Richard W. Byrne
Part Five – Group Movement from a Wider Taxonomic Perspective
18. Birds of Many Feathers: The Formation and Structure of Mixed-Species Flocks of Forest Birds by Russell Greenberg
19. Keeping in Touch at Sea: Group Movement in Dolphins and Whales by Rachel Smolker
20. Group Travel in Social Carnivores by Kay E. Holekamp, Erin E. Boydston, and Laura Smale
21. Ecological Correlates of Home Range Variation in Primates: Implications for Hominid Evolution by William R. Leonard and Marcia L. Robertson
22. Patterns and Processes of Group Movement in Human Nomadic Populations: A Case Study of the Turkana of Northwestern Kenya by J. Terrence McCabe
Concluding Remarks
New Directions for Group Movement by Sue Boinski and Paul A. Garber
The book is ten years old, but still forms the basis for the relevant literature. Two more or less startling conclusions emerge from the papers in this volume: 1) In primates, there is no apparent association between the mechanisms or abilities of various primate species to coordinate movement or to find food or other resources as a group and the species’ taxonomy. In other words, primate behavior at this level is not determined by phylogeny, and thus, not determined by genes. Or, to be more precise, variation in primate capacities to carry out this complex set of behaviors is not explained by innate programming. This is important when thinking, for instance, of human culture and human variation in behavior, intelligence, or other brain-related features. While modern pseudo-evolutionary pop psychologists are busy telling us that they can predict differences in capacities of humans by ethnicity, national origin, skin color, etc. we find no such predictive power in a major complex behavior across primate species as different as ape vs. monkey or old world primate vs. new world primate. This underscores the degree to which it is essentially a primate thing to not be overly programmed in behavior by some genetic code.
The second finding I’d like to mention is that in many (most?) of the species studied, sociability determines the nature of group movement more than does ecological demand or foraging efficiency. In human forager studies over the last few decades, it was discovered much to the chagrin of many anthropologists that foraging behavior was more often determined by non-optimization effects. Human foragers don’t maximize caloric or protein intake, or optimize hunting or gathering behavior, as much as most researchers thought they would. Well, it turns out that that’s a primate-wide trait. We shouldn’t have expected it. Food is paramount, and much of the overarching behavior of primates does relate to it, but the day to day, or hour to hour optimization that optimal foraging theory predicted simply does not signify.
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