HomeGlossary Bird topography Casque A helmet-like growth on top of the bill or head. Found in hornbills and cassowaries; its size and colour are key identification features. Bird topographyRelated termsFull glossary Supercilium A pale stripe above the eye, often called the eyebrow. Coverts Small feathers that overlap the bases of the flight and tail feathers, on both upper and under surfaces. Tarsus The lower, usually bare, part of the leg above the toes. Tertials The innermost flight feathers, next to the body, which often cover the folded primaries on a perched bird. Speculum A bright, often iridescent patch on the secondaries of many ducks. Rump The lower back, just above the base of the tail.
Coverts Small feathers that overlap the bases of the flight and tail feathers, on both upper and under surfaces.
Tertials The innermost flight feathers, next to the body, which often cover the folded primaries on a perched bird.