Behavioral Ecology and Sociobiology

, Volume 29, Issue 4, pp 271–276 | Cite as

Safety in numbers: shoal size choice by minnows under predatory threat

  • Mary C. Hager
  • Gene S. Helfman


Larger animal groups often provide greater protection from predators. An individual might therefore be expected to join the larger of two groups. To test this, we hypothesized that fathead minnows would choose to associate with the larger of two shoals and that the presence of a predatory largemouth bass would influence their shoal size choice. Individual minnows were presented with a series of choices between two shoal sizes, ranging from 1 to 28 fish, both with and without a predator present. Although responses were highly variable, minnows displayed an ability to choose between shoal sizes even when size differences were small, preferring the larger shoal whenever a size preference was shown. In the presence of a predator, minnows made quicker shoaling decisions and showed a strong tendency to avoid very small shoals.


Size Difference Strong Tendency Large Animal Animal Group Largemouth Bass 
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  1. Alexander RD (1974) The evolution of social behavior. Annu Rev Ecol Syst 5:325–338Google Scholar
  2. Allan JR, Pitcher TJ (1986) Species segregation during predator evasion in cyprinid shoals. Freshw Biol 16:653–659Google Scholar
  3. Butler MJ (1988) In situ observations of bluegill (Lepomis macrochirus Raf.) foraging behavior: the effects of habitat complexity, group size, and predators. Copeia 1988:939–944Google Scholar
  4. Calvert WH, Hedrick LE, Brower LP (1979) Mortality of the monarch butterfly (Danaus plexippus L.): Avian predation at five overwintering sites in Mexico. Science 204:847–850Google Scholar
  5. Cushing DH, Harden Jones FR (1968) Why do fish school? Nature 218:918–920Google Scholar
  6. Godin J-GJ (1986) Antipredator function of shoaling in teleost fishes: A selective review. Nat Can 113:241–250Google Scholar
  7. Hamilton WD (1971) Geometry for the selfish herd. J Theor Biol 31:285–311Google Scholar
  8. Helfman GS (1984) School fidelity in fishes: the yellow perch pattern. Anim Behav 32:663–672Google Scholar
  9. Hoogland JL (1981) The evolution of coloniality in white-tailed and black-tailed prairie dogs (Sciuridae: Cynomys leucurus and C. ludovicianus). Ecology 62:252–272Google Scholar
  10. Keenleyside MHA (1955) Some aspects of the schooling behaviour of fish. Behaviour 8:83–248Google Scholar
  11. Landeau L, Terborgh J (1986) Oddity and the “confusion effect” in predation. Anim Behav 34:1372–1380Google Scholar
  12. Lehner PN (1979) Handbook of Ethological Methods. Garland STPM Press, New YorkGoogle Scholar
  13. Major PF (1978) Predator-prey interactions in two schooling fishes, Caranx ignobilis and Stolephorus purpureus. Anim Behav 26:760–777Google Scholar
  14. Milinski M (1984) A predator's costs of overcoming the confusion-effect of swarming prey. Anim Behav 32:1157–1162Google Scholar
  15. Morgan MJ, Colgan PW (1987) The effects of predator presence and shoal size on foraging in bluntnose minnows, Pimephales notatus. Env Biol Fish 20:105–111Google Scholar
  16. Morgan MJ, Godin J-GJ (1985) Antipredator benefits of schooling behavior in a cyprinodontid fish, the banded killifish (Fundulus diaphanus). Z Tierpsychol 70:236–246Google Scholar
  17. Neill SRStJ, Cullen JM (1974) Experiments on whether schooling by their prey affects the hunting behaviour of cephalopods and fish predators. J Zool (Lond) 172:549–556Google Scholar
  18. Parrish JK (1988) Re-examining the selfish herd: are central fish safer? Anim Behav 38:1048–1053Google Scholar
  19. Partridge BL (1980) The effect of school size on the structure and dynamics of minnow schools. Anim Behav 28:68–77Google Scholar
  20. Pitcher TJ (1983) Heuristic definitions of shoaling behaviour. Anim Behav 31:611–613Google Scholar
  21. Pitcher TJ (1986a) Functions of shoaling behavior in teleosts. In: Pitcher TJ (ed) The behaviour of teleost fishes. Croom Helm, Beckenham, Kent, pp 294–337Google Scholar
  22. Pitcher TJ (1986b) Predators and food are the keys to understanding fish shoals: A review of recent experiments. Nat Can 113:225–233Google Scholar
  23. Pulliam HR, Caraco T (1984) Living in groups: Is there an optimal group size? In: Krebs JR, Davies NB (eds) Behavioural Ecology, 2nd edn. Blackwell, Oxford, pp 122–142Google Scholar
  24. SAS (1985) SAS User's Guide: Statistics. SAS Institute, Cary, NCGoogle Scholar
  25. Savino JF, Stein RA (1989) Behavioural interactions between fish predators and their prey: effects of plant density. Anim Behav 37:311–321Google Scholar
  26. SPSS (1986) SPSS User's Guide, 2nd edn. McGraw-Hill Book Co. New York, NYGoogle Scholar
  27. Theodorakis CM (1989) Size segregation and the effects of oddity on predation risk in minnow schools. Anim Behav 38:496–502Google Scholar
  28. Tonn WM, Magnuson JJ (1982) Patterns in the species composition and richness of fish assemblages in northern Wisconsin lakes. Ecology 63:1149–1166Google Scholar
  29. Tremblay D, FitzGerald GJ (1979) Social organization as an antipredator strategy in fish. Nat Can 106:411–413Google Scholar
  30. Vine I (1971) Risk of visual detection and pursuit by a predator and the selective advantage of flocking behavior. J Theor Biol 30:405–422Google Scholar
  31. Vine I (1973) Detection of prey flocks by predators. J Theor Biol 40:207–210Google Scholar
  32. Wolf NG (1985) Odd fish abandon mixed-species groups when threatened. Behav Ecol Sociobiol 17:47–52Google Scholar

Copyright information

© Springer-Verlag 1991

Authors and Affiliations

  • Mary C. Hager
    • 1
  • Gene S. Helfman
    • 1
  1. 1.Department of Zoology and Institute of EcologyThe University of GeorgiaAthensUSA

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