Behavioral Ecology and Sociobiology

, Volume 65, Issue 12, pp 2197–2208

Same-sex pair-bonds are equivalent to male–female bonds in a life-long socially monogamous songbird

  • Julie E. Elie
  • Nicolas Mathevon
  • Clémentine Vignal
Original Paper


Same-sex sexual behaviors are well documented in both captive and wild animals. In monogamous species, these behaviors are often exclusive, each individual having only one same-sex partner. A bias in sex ratio has been proposed as a social context yielding same-sex pair-bonding, but this hypothesis has rarely been tested. Focusing on a life-long pair-bonding songbird, the zebra finch Taeniopygia guttata, we tested whether same-sex pairing results from a shortage of individuals of the opposite sex. By experimentally skewing the sex ratio towards members of one sex, we observed a greater proportion of same-sex pair-bonds of that sex. Moreover, we assessed whether the quality and stability of social interactions were equivalent in same-sex and male–female pairs. Male–male and female–female same-sex bonds display the same behavioral characteristics as male–female ones: they are intense, highly selective, and stable affinitive relationships involving the same behavioral displays already described in wild birds. Moreover, same-sex male bonds were sufficiently strong not to split up when individuals were given the opportunity to reproduce with females. Because the pair-bond in socially monogamous species represents a partnership that may give advantages for survival (e.g., resources defense, fighting against predators, etc.), we propose that same-sex pairing in the zebra finch may result from the pressure to find a social partner.


Animal homosexuality Zebra finch Same-sex sexual behavior Sex ratio Partnership Pair-bond Social network 



Allopreening bouts


Events of clumping and greeting beak fence


Courtship and copulation


Directed songs


Index of relationship strength


Daily value of IRS


Value of IRS computed over the whole experiment


Nest sharing


Outcome variable

Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Julie E. Elie
    • 1
    • 2
    • 3
  • Nicolas Mathevon
    • 1
    • 2
  • Clémentine Vignal
    • 1
    • 2
  1. 1.Équipe de Neuro-Éthologie Sensorielle/CNPSUniversité de Saint-Etienne, CNRS UMR 8195Saint-EtienneFrance
  2. 2.Centre de Neurosciences Paris Sud, CNRS UMR 8195Centre National de la Recherche ScientifiqueOrsayFrance
  3. 3.University of CaliforniaBerkeleyUSA

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