Endocrine influences on parental care during a short breeding season:: testosterone and male parental care in Lapland longspurs (Calcarius lapponicus)

In males of socially monogamous birds, plasma testosterone (T) typically declines to low levels during the parental phase. Studies on multiple-brooded species indicate that high T may be incompatible with high-quality paternal carl. The length of the breeding season may affect the costs and benefits of high T and its effect on paternal carl. We studied the effect of experimentally elevated T on paternal care in a single-brooded species with a short breeding season, the Lapland longspur (Calcarius lapponicus). We monitored T levels and parental behavior in 16 males with subcutaneous T implants, 14 males with empty implants, and 14 unimplanted males. We videotaped nests when nestlings were 2-3 days old and again at 4-5 days. T males with 2- to 3-day-old young visited nests and fed young less often than control males, and the mates of the T males compensated with elevated visits and feedings. However, when nestlings were 4-5 days old, T males visited their nests at normal rates - though feeding movements remained below normal - and T females visited and fed at normal rates. Nestling mass and nest success were similar in both groups. Overall. high T suppresses paternal care in Lapland longspur males. The partial improvement of paternal care when nestlings are older, despite high T, may be related to the Short 6-week breeding season of this arctic species, and the consequently reduced benefits of sexual behavior late in the breeding season.