TESTOSTERONE INDUCED DEPRESSION OF MALE PARENTAL BEHAVIOR IN THE BARNSWALLOW - FEMALE COMPENSATION AND EFFECTS ON SEASONAL FITNESS

In birds, many aspects of male socio-sexual and parental behavior are influenced by androgens, most notably testosterone (T). We report the effects of subcutaneous T-implants in male barn swallows (Hirundo rust ica) on male and female parental behavior and on seasonal reproductive success. Males were assigned to one of three experimental groups: (i) implanted with a T-filled Silastic tube; (ii) implanted with an empty Silastic tube; and (iii) not implanted. T-implanted males provided a smaller proportion of feedings (number of feedings by the male/total n umber of feedings by both parents) and fed nestlings less frequently ( number of feedings/h) than males of the other two groups. Females pair ed to T-implanted males fed nestlings significantly more often than fe males paired with unimplanted males. Females almost fully compensated for their mates' shortfall, and this resulted in similar combined feed ing efforts among treatments. Reproductive success in their first broo ds or during the entire breeding season was unaffected by T-treatment. These results confirm earlier resorts of the suppressive effects of T on male parental behavior. However, they are inconsistent with curren t ESS models that predict partial compensation as the optimal response by one individual to reduction of parental effort by its mate in mono gamous, biparental systems.