Behavioral Ecology and Sociobiology

, Volume 57, Issue 3, pp 215–223

Effects of testosterone on male-male competition and male-female interactions in blue tits

Original Article

DOI: 10.1007/s00265-004-0858-6

Cite this article as:
Foerster, K. & Kempenaers, B. Behav Ecol Sociobiol (2005) 57: 215. doi:10.1007/s00265-004-0858-6


In temperate-zone birds, testosterone (T) influences male behavior during the breeding season. The elevation of plasma levels of T to a breeding baseline is necessary for basic reproductive behaviors, but it is still unclear whether variation in T levels above this critical threshold influences the intensity of these behaviors. Such a relationship between T and sexually selected traits is a critical assumption of the immunocompetence handicap hypothesis. We here experimentally elevated T levels in blue-tit males above the natural mean (T-males) during the period of nest building and egg laying, without manipulating hormone levels during chick feeding. T-males neither interacted more often with other males, nor did they respond more aggressively to a dummy intruder, compared to males with control implants. T-males did not guard their social mates more closely, but they were more likely to interact with potential extra-pair mates. Females mated to T-males did not change their behavior during egg laying and the treatment did not significantly affect male and female feeding rates. Despite this, nests of T-males produced larger and heavier fledglings in one study year. Our observations suggest that T levels above the natural mean during the mating period do not increase aggressive or territorial behavior in male blue tits. However, if females perceived T-males as high-quality mating partners, superior offspring development in nests of T-males might be caused by higher maternal investment. Hence, male behaviors involved in mate attraction may have been influenced by T levels above the natural mean.


Parus caeruleus Aggression Mate choice Sexual selection Testosterone 

Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  1. 1.Reproductive Biology and Behaviour GroupMax Planck Institute for OrnithologyStarnberg (Seewiesen)Germany

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