In an aviary experiment carried out at the beginning of the breeding season in March and April, nest-box occupation and associated behaviours were observed in a group of 18 adult and 18 first-year male European starlings. Nine birds of each group carried a testosterone implant (T-males) and the other 9 an empty implant (C-males). When analyzed for effects of age, first year birds were significantly more active with regard to nest-box inspection and nest-building than adults. When analyzed for effects of treatment, T-males occupied more nest-boxes and visited their nest-boxes more often than C-males. Other activities like singing, nest-box inspection, nest-building and aggressive behaviour were not significantly different between T-males and C-males. We suggest that the absence of a significant effect of T on aggression may be related to the colonial nesting habits of the starling. Since T-males tended to be more active with regard to all behaviours studied testosterone may have led to a general increase in frequency and persistence of behaviour which in turn facilitated nest-box occupation.