Plasma androgen levels and body weights for breeding and nonbreeding male American Kestrels

Plasma androgen levels (1981) and body weights (1980 and 1981) were determined weekly between April and September for breeding and nonbreeding captive male American Kestrels (Falco sparverius) paired with females. Irrespective of breeding group, males exhibited comparable values for and weekly changes (P 2.73 + 0.76 ng/ml) in April and May, decreased to minimal values (50.30 ? 0.05 ng/ ml) by the second week of June, and remained relatively low through the end of September. Relative to the nesting stages, androgen levels for the breeding males peaked during both courtship stages and decreased (P 0.10) from each other. The difference (P < 0.01) between maximal (April, May, and September) and minimal (June, July, and August) body weights of males averaged 19%.