Sexual dimorphism and plumage characteristics of juvenile Cape Vultures Gyps coprotheres

Abstract

The plumage of young Cape Vultures Gyps coprotheres is streaked to varying degrees on the breast, ruff and upper wing coverts. Observations of breast plumage (individual feather streak coverage and overall streaking intensity) were made on Cape Vultures aged one to six years old. Juveniles, or birds in their first year, were genetically sexed. Standardised photographs were taken of plucked juvenile breast feathers and analysed using Adobe Photoshop. Pixel counts were taken to analyse the streak coverage of a single feather. A scale from 0 to 3 was used to score streak intensity of the entire breast. We determined that breast streaking can be used as a reliable sexing technique with males being more heavily streaked than females. However, streaking is quickly lost with age and is therefore likely only to be a significant sexing tool for juveniles. The streaking of the breast generally disappears by four years of age.

Keywords: Cape Vulture, Gyps coprotheres, plumage, sexual dimorphism, streaking