acta ethol (2004) 7: 9–18 DOI 10.1007/s10211-004-0091-3 ORIGINAL ARTICLE Didone Frigerio . Katharina Hirschenhauser . Erich Möstl . John Dittami . Kurt Kotrschal Experimentally elevated testosterone increases status signalling in male Greylag geese (Anser anser) Received: 2 January 2003 / Revised: 5 April 2004 / Accepted: 19 April 2004 / Published online: 15 July 2004 # Springer-Verlag and ISPA 2004 Abstract Testosterone modulates male vertebrates’ sexual and social behaviour. We experimentally investigated the testosterone-sensitive behaviours in male greylag geese (Anser anser) by implanting silastic tubes containing crystalline testosterone during the mating season (Febru- ary; 5 implanted and 5 control males) and in the early winter (November; 7 and 7). Focal animals were part of a semi-tame, unrestrained flock with fully intact social relationships. Excreted testosterone and corticosterone immunoreactive metabolites (TM, BM) were determined by enzyme immunoassay. Individual faecal samples and behavioural protocols were collected daily over a period of 5 weeks, including 1 control week before implantation. In February, no significant behavioural effects of the supple- mental testosterone were observed, which may be due to the naturally occurring high systemic androgen levels in spring. In November, however, implanted males had higher TM excretion rates and performed status signalling behaviour (“beak up”) more frequently than control males. No differences between implanted and control males were found with respect to BM, agonistic interactions or vigilance behaviour. Furthermore, during the second week after implantation, TM positively correlated with the frequency of “beak up” of implanted males, whilst their female partners were attacked with lower latency by other members of the flock than the females of control males. Hence, status signalling in greylag ganders seems to be testosterone-sensitive year-long and “inappropriate” status signalling of males may draw attacks towards their females. Keywords Anser anser . Corticosterone . Faeces . Status signalling behaviour . Testosterone implantation Introduction Gonadal steroid hormones modulate sexual and agonistic behaviour in vertebrates (e.g. fishes: Oliveira et al. 1996; amphibians: Houck and Woodley 1995; reptilians: Moore and Thompson 1990; birds: Wingfield et al. 1990; or mammals: Woodroffe et al. 1997). Behaviour, in turn, can produce feed-back modulation on the endocrine system (e.g. Hegner and Wingfield 1986; Wingfield et al. 1990; Knapp and Moore 1996; Wikelski et al. 1999). In particular, studies on male birds have shown that testos- terone (T) is involved in modulating sexual and social behaviours, for example by mediating the trade-off between sexual and parental investment (e.g. Rissman and Wingfield 1984; Ketterson and Nolan 1992; Wikelski et al. 1999). High T levels may also promote acoustic communication (e.g. Ketterson et al. 1992; Hunt et al. 1997) and further social status (e.g. Searcy and Wingfield 1980; Hoysak and Ankney 1996). Experimentally increased systemic T is known to change the level of expression of androgen-sensitive behaviours, for example by promoting polygynous mating (e.g. Hegner and Wingfield 1987; Ketterson and Nolan 1992), inhibiting paternal care (e.g. Dittami et al. 1991; Cawthorn et al. 1998) or facilitating territoriality (e.g. Wingfield and Hahn 1994). However, elevated T may also impose costs by suppressing immuno-competence and increasing mortality (e.g. Saino et al. 1995; Ros 1999; Wingfield et al. 1999) or by delaying moult (e.g. Schleussner et al. 1985). Although many studies demonstrated that T secretion in spring was related to the expression of aggressive behaviour (e.g. Wingfield and Ramenofsky 1985; Wing- Communicated by R.F. Oliveira D. Frigerio (*) . K. Hirschenhauser . J. Dittami . K. Kotrschal Konrad Lorenz Forschungsstelle für Ethologie and Department of Zoology, University of Vienna, Grünau 11, 4645 Vienna, Austria e-mail: klf.gruenau@telecom.at Tel.: +43-7616-8510 Fax: +43-7616-85104 E. Möstl Institute for Biochemistry, University of Veterinary Medicine, Vienna, Austria