Effects of testosterone on use of space by male dark-eyed juncos when their mates are fertile

Testosterone is an important determinant of spatial activity in male birds. Using radiotelemetry, male dark-eyed juncos, Junco hyemalis, were followed during the period when their mates were fertile to investigate the relationship between testosterone and behaviours (territoriality, consorting with female) through which males might guard paternity. Males with experimentally elevated testosterone levels (T-males) and control males (C-males) did not differ significantly in their use of space during this period. T-males and C-males occupied similar home ranges, used similar-sized core areas (areas enclosing 95% of all activity), spent similar amounts of time close to their mates, and experienced similar intrusion rates onto their territories. Experimentally elevating testosterone above control levels did not detectably affect the spatial activity of male juncos during the female fertile period, although earlier studies have shown that its effects are pronounced during other stages of the nesting cycle. (C) 1997 The Association for the Study of Animal Behaviour.