Delayed plumage maturation in the Tawny-bellied Seedeater (Sporophila hypoxantha)

FACCHINETTI, C.; DI GIACOMO, A. G.; MAHLER, B.; REBOREDA, J.C.

Congreso; 25th International Ornithological Congress; 2010

Differences in avian and human visual systems sometimes conceal plumage color differences to the human eye that are however perceived by birds. The Tawny-bellied Seedeater (Sporophila hypoxantha) is sexually monogamous and dichromatic species, but it is virtually impossible for the human eye to distinguish between females and juveniles. We analyzed plumage maturation in this species using reflectance spectrometry. We captured 52 individuals at Formosa Province, Argentina, and maintained them in captivity until they completed the first post-reproductive molt. We analyzed plumage coloration in three groups: adult males, females and juvenile males. All individual were sexed genetically. We took measurements on four body parts (throat, breast, belly and crown) and calculated four spectra variables (brightness, UV-blue chroma, green chroma and red chroma). Spectrometrical analyses confirmed color differences observed between adult male and female plumage, and unveiled color differences between the plumage of females and juvenile males. Juvenile males also differed from adult males throughout the first year, but this difference disappeared in after one-year old individuals in almost every measured body region, except for crown plumage, where they still differed from adult males in all variables except in brightness. Our results indicate that Tawny-bellied Seedeaters have delayed plumage maturation and during the first breeding season one-year old males differ from older ones. Whether females are capable to distinguish these plumage color differences and choose males accordingly still deserves further research.