Sexual dimorphism and species differences in HVC volumes of cowbirds

HAUBER, ME; CLAYTON, NS; KACELNIK, A; JUAN C. REBOREDA; DEVOOGD, TJ

Behavioral Neuroscience

Año: 1999 vol. 113 p. 1095 - 1099

Cowbirds exhibit extensive variation in their social and territorial behaviors as well as in their mating and reproductive strategies. Using Nissl-stained brain sections of specimens from a previous study (Reboreda et al., 1996), we studied the gross anatomy of a song control nucleus in three South American cowbirds (Bay-winged, Molothrus badius; Shiny, M. bonariensis, and Screaming, M. rufoaxillaris:) to estimate relative variation in the vocal behavior and song complexity of these species. As in most other songbirds, cowbird HVC volumes were consistently higher in males than in females in all three species. Largest HVC size of females in Bay-winged Cowbirds is consistent with observations that females of this species, but not of the other two species, occasionally sing. The extent of the sexual dimorphism of relative HVC size was highest for the sexually dichromatic and promiscuous Shiny Cowbirds and smaller for the sexually monochromatic and monogamous Bay-winged and Screaming Cowbirds, suggesting that selection pressures associated with different morphological traits and social systems are reflected in brain architecture.