Low variation of retinal size and relative expansion velocity (RREV) of the approached perch suggests these cues matter for controlled landings on a swinging perch.

We defined the tail pitch as the behavioral indicator for landing initiation (time = 0 ms). Negative time values represent the time before and positive time values the time after the downward pitch of the tail feathers. Shaded areas ranging from -30 ms to 0 ms mark the minimal time period of visuomotor delay during which visual flight control is unlikely. Absolute horizontal flight speed (A) has less variation across flights than relative horizontal flight speed (B) with respect to the moving perch. (C) The most parsimonious landing parameters are indicated by a minimum in the coefficient of variation (c.v.) across flights and birds. The retinal size (orange) and RREV (green) for the approached perch varied less that the parameter tau and the retinal expansion. Tail pitch timing was extracted individually from high-speed flight videos. n = 16, N = 5 birds.