The natural plasma testosterone profile of male blue tits during the breeding season and its relation to song output

K. Foerster, A. Poesel, Hansjoerg Kunc, B. Kempenaers

Research output: Contribution to journalArticlepeer-review

39 Citations (Scopus)

Abstract

In male birds, the gonadal hormone testosterone (T) is known to influence territorial and mating behaviour. Plasma levels of T show seasonal fluctuations which vary in relation to mating system and social instability. First, we determined the natural T profile of male blue tits Parus caeruleus during the breeding season. We found that plasma levels of T increased at the onset of nest building. Thus, the increase in circulating T was not associated with territory establishment, nor with the fertile period of the males' mates. In most individuals, T levels dropped to values close to zero during the period of chick feeding. Second, we investigated the relationship between plasma levels of T and male age, size, and singing behaviour. During the mating period, T levels did not differ between 1 yr old and older males and did not correlate with body size or condition. However, song output during the dawn chorus tended to be positively correlated with T levels. Therefore, if high T levels are costly, song output might be an honest indicator of male quality in blue tits. Finally, we show that plasma levels of T are significantly higher during the night than during the day. This pattern has also been observed in captive non-passerine birds, but its functional significance remains unknown.
Original languageEnglish
Pages (from-to)269-275
Number of pages7
JournalJournal of Avian Biology
Volume33
Issue number3
Publication statusPublished - Sep 2002

ASJC Scopus subject areas

  • Animal Science and Zoology

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