A RARE MUTUAL COURTSHIP DISPLAY IN A SOUTH AMERICAN PASSERIFORMES: BLUE-BILLED BLACK-TYRANT (KNIPOLEGUS CYANIROSTRIS) (TYRANNIDAE: FLUVICOLINAE)

Abstract

Territorial displays are a common behavior in Knipolegus, but are only performed by males, while a mutual displays are unknown in this genus. In October 2012, in high-altitude grassland (Campos de Altitude), Espírito Santo state, south-east Brazil, a pair of Blue-billed Black Tyrant Knipolegus cyanirostris was filmed making very curious and subtle movements. Both individuals were silent, and perched facing each other 0.59–0.75 m apart, with the male slightly lower, at an angle of c. 21°–23° below the female. The male moved its head downwards, moving its bill in a pendulum-like, downward motion, then reassumed its upright stance, while the female, with its head slightly bent down, moved its bill in the same way as the male, before also reassuming her original stance. These movements were very fast and almost impossible to see with the human eye. This mutual display suggests that courtship behavior in Knipolegus may be much more complex than is currently believed