American Kestrel (Falco sparverius) Science Article 7
We studied the acoustical characteristics of calls made by nestling American Kestrels (Falco sparverius). A total of 563 vocal samples was obtained from 88 chicks (49 males and 39 females) from 20 broods. Thirteen frequency, three numerical, and two temporal characteristics were measured using audio spectrography. Discriminant function analysis failed to distinguish the calls of male and female chicks, but univariate and principal component analyses suggest that vocal ontogeny proceeds more rapidly in males than in females. The acoustical characteristics of call notes changed in a consistent manner as nestlings matured, and by day 16 chicks produced calls similar to those of adults.
JOHN A. SMALLWOOD et al., j. Raptor Res. 37(1):37-43