Purple Martins

Progne subis

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Why are some animals colonial?

Why do some animals form monogamous pair bonds and then cheat on their mates?

The evolution of colonial living undoubtedly involves advantages from this life style for ecological and behavioral reasons. Drs. Richard Wagner, Eugene Morton and myself have studied the incidence of multiple paternity in purple martins living in Front Royal, Virginia. We showed that females prefer to form social bonds with older males. Females who pair-bond with younger males often cheat on them by soliciting copulations from older males in the colony. Dr. Wagner has proposed that this is a strategy that has evolved in purple martins that may underly the evolution of colonial living itself. Purple martins may form a 'hidden lek' in which coloniality provides opportunities for females to mate with males outside of their pair-bond to increase their reproductive success. So in addition to any ecological benefits to colonial living, the opportunity it provides for cheating on mates may itself drive the evolution of colony formation.

This is a remarkable hypothesis in itself, but even more remarkable because we can test it using available field and laboratory techniques. Our first goal is to find what it is about the old males that females prefer. Some ideas are their health in general, the vigor of their song, their social dominance, their color, or their genetic relationship to prospective mates.

  • Wagner, Richard H., Malcolm D. Schug, Eugene S. Morton.  1997.  Studying paternity and paternal care: the value of negative results.  Animal Behaviour 55:239-240.
  • Wagner, Richard, Malcolm D. Schug, Eugene S. Morton.  1997.  Do blood parasites affect paternity, provisioning and mate-guarding in purple martins?  Condor 99:520-523.
  • Wagner, Richard, Malcolm D. Schug, Eugene S. Morton.  1996.  Condition dependent control of paternity by female purple martins: implications for coloniality.  Behavioral Ecology and Sociobiology 38: 379-389.
  • Wagner, Richard, Malcolm D. Schug, Eugene S. Morton.  1996.  Confidence of paternity, actual paternity, and parental effort by purple martins.  Animal Behaviour 52:123-132.