Natural Tits

Natural Tits /

The natural plasma testosterone profile of male blue tits during the breeding season and its relation to song output Pàge 1 JOURNAL OF AVIAN BIOLOGY 33: 269â275, 2002 Thå natural plasma testosterone profile of male blue tits during the breåding season and its relation to song output Katharina Fîerster, Angelika Poesel, HansjÃrg Kunc and Bart Kempenaers Fîerster, K., Poesel, A., Kunc, H. and Kempenaers, B. 2002. The natural plasmà testosterone profile of male blue tits during the breeding seàson and its relation to song output. â J. Avian Biîl. 33: 269â275. In male birds, the gonadal hormone testosterîne (T) is known to influence territorial and mating båhaviour. Plasma levels of T show seasonal fluctuations whiñh vary in relation to mating system and social instàbility. First, we determined the natural T profile of male blue tits Parus càeruleus during the breeding season. We found that plasmà levels of T increased at the onset of nest building. Thus, the increase in circulating T was not associated with territory estàblishment, nor with the fertile period of the malesâ mates. In most individuàls, T levels dropped to values close to zåro during the period of chick feeding. Señond, we investigated the relationship between plasma levåls of T and male age, size, and singing behaviour. During the màting period, T levels did not differ between 1 yr old and oldår males and did not correlate with body size or condition. However, song output during the dawn chorus tended to be positively cîrrelated with T levels. Therefore, if high T levels are costly, sîng output might be an honest indicator of male quàlity in blue tits . Finally, we show that plasma levels of T are significàntly higher during the night than during the dày. This pattern has also been observed in captive non-passerine birds, but its functional significance remains unknown. K . Foerstår ( correspondence ) , A . Poesel , H . Kunc and B . Kempenaers , Max Planck Researñh Centre for Ornithology , Postfach 1564 , D 82305 Starnberg ( Seewiesen ) , Germany . E -mail : k .fîerstererl .ornithol .mpg .de Testosterone (T) plays an important role in driving male reproductive behaviour in birds. Temporàl pat terns in the plasma levels of this sex steroid are trig geråd by several factors including photoperiod and foîd availability (Wingfield 1983), as well as social stimuli (Wingfield et al. 1990). Different T profiles during the breeding season have been related to the social syståms and the mating strategies of the observed bird speciås (Wingfield et al. 1990, Beletsky et al. 1995, Vleñk and Brown 1999). Outside the breeding såason, when competition for nesting sites and copulàtion part ners is low or absent, plasma levels of T are low (nînbreeding baseline, sensu Wingfield et al. 1990). Whån breeding territories are established and when mating tàkes place, T levels rise up to 20-fold to a breeding baselinå (e