aru takasa ika-o jiyuu-ni kuroageha
below a certain height
flying any way it likes
Koui Nagata (1900-1997). From "Romeishuu" (Brays from a Donkey), HarimaHaiwaKai, 1953.
Wind speed increases with altitude, so the higher above the ground a butterfly flies, the more buffeted it would be by the wind. The poet has been watching the swallowtail fly and has observed that above a certain height, that is indeed the case. However, rather than concretely describing how it loses control high in the air, instead the poet focuses on how free the butterfly is when it doesn't push the boundaries.
Selected, translated and commented on by Dhugal J. Lindsay