LYNN, S.E*; WINGFIELD, J.C.: Sensitivity to supplementary testosterone during the parental phase in a high arctic breeding passerine

In avian species that show paternal care, males� testosterone (T) levels peak early in the breeding season, and then decline through the parental phase. This may be related to a trade-off between T and paternal care: T tends to enhance sexual behavior at the expense of parental behavior. In most species, experimental extension of the early T peak throughout the parental phase reduces nestling provisioning behavior by males. However, several studies suggest that this is not a universal phenomenon. Insensitivity to T during the parental phase has been demonstrated in arctic breeding Lapland longspurs (Calcarius lapponicus) and mid-latitude breeding Chestnut-collared longspurs (C. ornatus). One possible hypothesis to explain T insensitivity in these species is that T insensitivity may arise when paternal care is essential for nestling success. However, that two congeners exhibit T insensitivity suggests there may be a phylogenetic confound. We examined the effects of supplementary T on paternal behavior in the high arctic breeding snow buntings (Plectrophenax nivalis), a close relative of the longspurs. P. nivalis males are not critical for survival of nestlings, and we predicted that extension of the early T peak would decrease paternal care in this species. We compared nestling provisioning rates of males implanted with T and males given empty implants. There was a strong trend for T-implanted males to feed their nestlings less than controls. Although males and females of control pairs fed their young at equal rates, T-implanted males fed their young significantly less than did their social mates. These data support the hypothesis that T insensitivity may arise when males are essential for fledging success.